Article

ENSO and PDO Effects on Hydroclimatic Variations of the Upper Colorado River Basin

Authors:
Article

ENSO and PDO Effects on Hydroclimatic Variations of the Upper Colorado River Basin

If you want to read the PDF, try requesting it from the authors.

Abstract

Linkages between tropical Pacific Ocean monthly climatic variables and the Upper Colorado River basin (UCRB) hydroclimatic variations from 1909 to 1998 are analyzed at interseasonal timescales. A study of the changes in these linkages through the years and their relationship to the Pacific Decadal Oscillation (PDO) is also investigated. Tropical Pacific climate variations were represented by atmospheric/oceanic ENSO indicators. For the UCRB, warm season (April-September) streamflow totals at Lee's Ferry, Arizona, and precipitation averages at different periods (cold season: October-March; warm season: April-September; and annual: October-September) were used to study the UCRB's response to tropical Pacific climatic forcing. A basinwide ENSO signature was found in the significant correlations between warm season precipitation in the UCRB and warm season SST averages from the Niño-3 region in most of the stations around the UCRB. This link is more evident during the warm phase of ENSO (El Niño), which is associated with an increase in warm season precipitation. The analysis also showed a link between June to November ENSO conditions and cold season precipitation variations contained in a principal component representing the high-elevation precipitation stations, which are the main source of streamflow. However, the amplitude and coherence of the cold season ENSO signal is significantly smaller compared to the general precipitation variations found in stations around the UCRB. Only when very few stations in the high elevations are considered is the ENSO signal in cold season precipitation in the basin revealed. Interdecadal hydroclimatic variations in the UCRB related to possible PDO influences were also investigated. There are significant shifts in the mean of UCRB's moisture-controlled variables (precipitation and streamflow) coincident with the PDO shifts, suggesting a connection between the two processes. It has been suggested in other studies that this connection could be expressed as a modulation on the predominance of each ENSO phase; that is, strong and consistent winter El Niño (La Niña) patterns are associated with the positive (negative) phase of the PDO. In the UCRB this apparent modulation seems to be accompanied by a general change in the sign of the correlation between ENSO indicators and cold season precipitation in most stations of the basin around 1932/33. From 1909 to 1932 the basin has a predominantly cold season ENSO response characteristic of the northwestern United States (drier than normal associated with tropical SST warming and vice versa); from 1933 to 1998 the response of the basin is predominantly typical of the southwestern United States during winter (wetter than normal associated with tropical SST warming and vice versa). This apparent correlation sign reversal is suggested to be related to interdecadal changes in the boundary of the north-south bipolar response characteristic of the ENSO signal in the western United States during winter.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... Precipitation and flooding in the LCRB are caused by convective-type storms, including those generated by the North American Monsoon (NAM), and frontal-type and tropical storms sourced from the Pacific Ocean and the Gulf of California (House and 15 Hirschboeck, 1997; Etheredge et al., 2004). In the UCRB, the influence of the NAM and tropical storms is diminished and floods are generally caused by Pacific frontal-type storms (Hidalgo and Dracup, 2003). In both regions, the El Niño Southern Oscillation (ENSO) alters the frequency and intensity of the NAM, tropical storms, and the Pacific frontal systems, and can cause annual variations in precipitation and flooding (House 20 and Hirschboeck, 1997; Hidalgo and Dracup, 2003). ...
... In the UCRB, the influence of the NAM and tropical storms is diminished and floods are generally caused by Pacific frontal-type storms (Hidalgo and Dracup, 2003). In both regions, the El Niño Southern Oscillation (ENSO) alters the frequency and intensity of the NAM, tropical storms, and the Pacific frontal systems, and can cause annual variations in precipitation and flooding (House 20 and Hirschboeck, 1997; Hidalgo and Dracup, 2003). Winter storms in both regions are also intensified by the occurrence of atmospheric rivers (Dettinger et al., 2011), which can cause total winter precipitation to increase up to approximately 25 % (Rutz and Steenburgh, 2012). ...
... To address whether or not the sample time interval used in this study includes major changes in circulation and weather patterns, and therefore is a good representation of climate in the CRB, we investigated the effect of the El Niño Southern Oscillation (ENSO) on precipitation intensity within the UCRB and LCRB. ENSO is a well-known important influence on the hydroclimatology of the west- 15 ern US (Hidalgo and Dracup, 2003; Cañon et al., 2007). In general, winter precipitation in the southwestern US increases during El Niño events and decreases during La Niña events (Hidalgo and Dracup, 2003). ...
Article
Full-text available
Flood-envelope curves (FEC) are useful for constraining the upper limit of possible flood discharges within drainage basins in a particular hydroclimatic region. Their usefulness, however, is limited by their lack of a well-defined recurrence interval. In this study we use radar-derived precipitation estimates to develop an alternative to the FEC method, i.e. the frequency-magnitude-area-curve (FMAC) method, that incorporates recurrence intervals. The FMAC method is demonstrated in two well-studied U.S. drainage basins, i.e. the Upper and Lower Colorado River basins (UCRB and LCRB, respectively), using Stage III Next-Generation-Radar (NEXRAD) gridded products and the diffusion-wave flow-routing algorithm. The FMAC method can be applied worldwide using any radar-derived precipitation estimates. In the FMAC method, idealized basins of similar contributing area are grouped together for frequency-magnitude analysis of precipitation intensity. These data are then routed through the idealized drainage basins of different contributing areas, using contributing-area-specific estimates for channel slope and channel width. Our results show that FMACs of precipitation discharge are power-law functions of contributing area with an average exponent of 0.79 ± 0.07 for recurrence intervals from 10 to 500 years. We compare our FMACs to published FECs and find that for wet antecedent-moisture conditions, the 500-year FMAC of flood discharge in the UCRB is on par with the US FEC for contributing areas of ~ 102 to 103 km2. FMACs of flood discharge for the LCRB exceed the published FEC for the LCRB for contributing areas in the range of ~ 102 to 104 km2. The FMAC method retains the power of the FEC method for constraining flood hazards in basins that are ungauged or have short flood records, yet it has the added advantage that it includes recurrence interval information necessary for estimating event probabilities.
... Precipitation and flooding in the LCRB are caused by convective-type storms, including those generated by the North American Monsoon (NAM), and frontal-type and tropical storms sourced from the Pacific Ocean and the Gulf of California (House and Hirschboeck, 1997;Etheredge et al., 2004). In the UCRB, the influence of the NAM and tropical storms is diminished and floods are generally caused by Pacific frontal-type storms (Hidalgo and Dracup, 2003). In both regions, the El Niño-Southern Oscillation (ENSO) alters the frequency and intensity of the NAM, tropical storms, and the Pacific frontal systems, and can cause annual variations in precipitation and flooding (House and Hirschboeck, 1997;Hidalgo and Dracup, 2003). ...
... In the UCRB, the influence of the NAM and tropical storms is diminished and floods are generally caused by Pacific frontal-type storms (Hidalgo and Dracup, 2003). In both regions, the El Niño-Southern Oscillation (ENSO) alters the frequency and intensity of the NAM, tropical storms, and the Pacific frontal systems, and can cause annual variations in precipitation and flooding (House and Hirschboeck, 1997;Hidalgo and Dracup, 2003). Winter storms in both regions are also intensified by the occurrence of atmospheric rivers (Dettinger et al., 2011), which can cause total winter precipitation to increase up to approximately 25 % (Rutz and Steenburgh, 2012). ...
... To address whether or not the sample time interval used in this study includes major changes in circulation and weather patterns, and therefore is a good representation of climate in the CRB, we investigated the effect of the ENSO on rainfall intensity within the UCRB and LCRB. ENSO is a well-known important influence on the hydroclimatology of the western US (Hidalgo and Dracup, 2003;Cañon et al., 2007). In general, winter precipitation in the southwestern US increases during El Niño events and decreases during La Niña events (Hidalgo and Dracup, 2003). ...
Article
Full-text available
Flood-envelope curves (FECs) are useful for constraining the upper limit of possible flood discharges within drainage basins in a particular hydroclimatic region. Their usefulness, however, is limited by their lack of a well-defined recurrence interval. In this study we use radar-derived precipitation estimates to develop an alternative to the FEC method, i.e., the frequency–magnitude–area-curve (FMAC) method that incorporates recurrence intervals. The FMAC method is demonstrated in two well-studied US drainage basins, i.e., the Upper and Lower Colorado River basins (UCRB and LCRB, respectively), using Stage III Next-Generation-Radar (NEXRAD) gridded products and the diffusion-wave flow-routing algorithm. The FMAC method can be applied worldwide using any radar-derived precipitation estimates. In the FMAC method, idealized basins of similar contributing area are grouped together for frequency–magnitude analysis of precipitation intensity. These data are then routed through the idealized drainage basins of different contributing areas, using contributing-area-specific estimates for channel slope and channel width. Our results show that FMACs of precipitation discharge are power-law functions of contributing area with an average exponent of 0.82 ± 0.06 for recurrence intervals from 10 to 500 years. We compare our FMACs to published FECs and find that for wet antecedent-moisture conditions, the 500-year FMAC of flood discharge in the UCRB is on par with the US FEC for contributing areas of ∼ 102 to 103 km2. FMACs of flood discharge for the LCRB exceed the published FEC for the LCRB for contributing areas in the range of ∼ 103 to 104 km2. The FMAC method retains the power of the FEC method for constraining flood hazards in basins that are ungauged or have short flood records, yet it has the added advantage that it includes recurrence-interval information necessary for estimating event probabilities.
... To increase the prospect of long-lead forecasts of the UCRB hydroclimate systems (e.g., streamflow and precipitation), previous studies have investigated the relationship between the UCRB hydroclimate systems and large-scale climatic teleconnections, such as those related to sea surface temperature (SST) (e.g., Kim et al. 2006;Regonda et al. 2006;Switanek et al. 2009;Bracken et al. 2010;Kalra and Ahmad 2011;Sagarika et al. 2015Sagarika et al. , 2016Zhao et al. 2021). Numerous studies focused on the role of Pacific and Atlantic SST, especially the El Niño-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and Atlantic Multidecadal Oscillation (AMO) (e.g., Hidalgo and Dracup 2003;Kim et al. 2006;Kalra and Ahmad 2011;Nowak et al. 2012;McGregor 2017;Tamaddun et al. 2017Tamaddun et al. , 2019Zhao et al. 2021;Zhao and Zhang 2022). An early study showed that the UCRB streamflow has a higher correlation with the AMO compared to other indices associated with the Pacific and Indian Oceans on decadal-to-multidecadal time scales (McCabe et al 2007), while a recent study found a stronger correlation between the Pacific SST and the UCRB streamflow in recent decades on interannual time scales (Zhao et al. 2021). ...
... An early study showed that the UCRB streamflow has a higher correlation with the AMO compared to other indices associated with the Pacific and Indian Oceans on decadal-to-multidecadal time scales (McCabe et al 2007), while a recent study found a stronger correlation between the Pacific SST and the UCRB streamflow in recent decades on interannual time scales (Zhao et al. 2021). For precipitation, Hidalgo and Dracup (2003) showed that the UCRB precipitation during the warm (cold) season is strongly (weakly) correlated to the El Niño. Similarly, Kim et al. (2006) found that the warm phase of the ENSO is associated with precipitation increase during summer in the UCRB, whereas its cold phase is linked to precipitation reduction during winter in the lower basin. ...
... Following previous studies that highlight the effect of the Pacific and North Atlantic SSTs (especially those related to ENSO, PDO, and AMO) on the UCRB precipitation (e.g., Hidalgo and Dracup 2003;Kim et al. 2006;Kalra and Ahmad 2011;Nowak et al. 2012;McGregor 2017;Tamaddun et al. 2017Tamaddun et al. , 2019Zhao et al. 2021;Zhao and Zhang 2022), we calculate the correlation coefficient between the UCRB averaged spring precipitation and SST for LD1-LD12. Figure 2 shows the correlation coefficient averaged over the period of 1980-2019 using the leave-three-out cross-validation. ...
Article
Full-text available
This study provides extended seasonal predictions for the Upper Colorado River Basin (UCRB) precipitation in boreal spring using an artificial neural network (ANN) model and a stepwise linear regression model, respectively. Sea surface temperature (SST) predictors are developed taking advantage of the correlation between the precipitation and SST over three ocean basins. The extratropical North Pacific has a higher correlation with the UCRB spring precipitation than the tropical Pacific and North Atlantic. For the ANN model, the Pearson correlation coefficient between the observed and predicted precipitation exceeds 0.45 (p-value < 0.01) for a lead time of 12 months. The mean absolute percentage error (MAPE) is below 20% and the Heidke skill score (HSS) is above 50%. Such long-lead prediction skill is probably due to the UCRB soil moisture bridging the SST and precipitation. The stepwise linear regression model shows similar prediction skills to those of ANN. Both models show prediction skills superior to those of an autoregression model (correlation < 0.10) that represents the baseline prediction skill and those of three of the North American Multi-Model Ensemble (NMME) forecast models. The three NMME models exhibit different skills in predicting the precipitation, with the best skills of the correlation ~ 0.40, MAPE < 25%, and HSS > 40% for lead times less than 8 months. This study highlights the advantage of oceanic climate signals in extended seasonal predictions for the UCRB spring precipitation and supports the improvement of the UCRB streamflow prediction and related water resource decisions.
... The role of the Pacific SST (predictor for long-lead streamflow prediction) in modulating the CRB precipitation (predictor for short-lead streamflow prediction) has been evaluated (e.g., Hidalgo and Dracup 2003;Kim et al. 2006). The SST variability associated with the El Niño-Southern Oscillation (ENSO; Cai et al. 2015a) provides dominant interannual variability in the equatorial Pacific. ...
... A warm phase of the ENSO leads to increasing precipitation in summer over the upper basin, while the cold phase of the ENSO leads to decreasing precipitation in winter over the lower basin (Wang and Ting 2000;Kim et al. 2006). For the UCRB, warm season precipitation was found to be more strongly linked to the El Niño (Niño 3 index) than cold season precipitation did (Hidalgo and Dracup 2003). ...
Article
Full-text available
The Colorado River is one of the most important rivers in the southwestern U.S., with ~ 90% of the total flow originating from the Upper Colorado River Basin (UCRB). The UCRB April–July streamflow is well-correlated to the UCRB spring precipitation. It is known that the UCRB precipitation is linked to an El Niño-like sea surface temperature (SST) pattern, but the causal effect of the tropical Pacific SST on the UCRB spring precipitation is still uncertain. Here, we apply a Granger causality approach to understand the causal effect of the tropical Pacific averaged SST in previous three seasons (winter, fall, and summer) on the UCRB averaged precipitation in spring in observations and two climate models. In observations, only the winter SST has Granger causal effect (with p-value ~ 0.05) on spring precipitation, while historical simulations of the two climate models overestimate the causal effect for winter and fall (with p-value < 0.01 and < 0.05, respectively) due to model biases. Moreover, future projections of the two climate models show divergent causal effects, especially for the scenario with high anthropogenic emissions. The divergent projections indicate that (1) there are large uncertainties in model projections of the causal effect of the tropical Pacific SST on UCRB spring precipitation and (2) it is uncertain whether climate models can reliably capture changes in such causality. These uncertainties may result in large uncertainties in seasonal forecasts of the UCRB hydroclimate under global climate change.
... The southwestern United States, including the upper Colorado River basin (UCRB), is highly vulnerable to regional climatic extremes, such as droughts and pluvials, because of the region's geographic location and climatological characteristics (Laird et al. 1996;Hidalgo 2004). Multiyear droughts and pluvials have severe consequences for the agricultural sector and water a The National Center for Atmospheric Research is sponsored by the National Science Foundation. ...
... The overall Colorado basin, whose water is often referred to as the life blood of the southwestern United States, supplies water for domestic use by approximately 26 million people, including residents of several major cities, such as Denver, and for various forms of recreation, irrigation, and hydropower production (Hidalgo 2004). ...
Article
This study analyzes spatial and temporal characteristics of multiyear droughts and pluvials over the southwestern United States with a focus on the upper Colorado River basin. The study uses two multiscalar moisture indices: standardized precipitation evapotranspiration index (SPEI) and standardized precipitation index (SPI) on a 36-month scale (SPEI36 and SPI36, respectively). The indices are calculated from monthly average precipitation and maximum and minimum temperatures from the Parameter-Elevation Regressions on Independent Slopes Model dataset for the period 1950-2012. The study examines the relationship between individual climate variables as well as large-scale atmospheric circulation features found in reanalysis output during drought and pluvial periods. The results indicate that SPEI36 and SPI36 show similar temporal and spatial patterns, but that the inclusion of temperatures in SPEI36 leads to more extreme magnitudes in SPEI36 than in SPI36. Analysis of large-scale atmospheric fields indicates an interplay between different fields that yields extremes over the study region. Widespread drought (pluvial) events are associated with enhanced positive (negative) 500-hPa geopotential height anomaly linked to subsidence (ascent) and negative (positive) moisture convergence and precipitable water anomalies. Considering the broader context of the conditions responsible for the occurrence of prolonged hydrologic anomalies provides water resource managers and other decision-makers with valuable understanding of these events. This perspective also offers evaluation opportunities for climate models.
... Through these interactions, the BRT allows for nonstationarity of the times eries (e.g., the effect of each PC is allowed to change over time). We fit BRTs using the "dismo" and "gbm" packages (Hijmans et al., 2017) in R (R Core Team, 2017). To cross-validate the BRTs for each lake, we fit the model using a training dataset and then used the fit BRT to predict monthly water levels using the PC values from a test dataset. ...
... Thus, excluding high-order PCs is unlikely to lead to substantial improvements or changes to our conclusions. The performance of the BRTs might be improved by including lag effects (Hansen et al., 1998;Hidalgo and Dracup, 2003). However, the computation time required to include lag effects was prohibitive. ...
Article
Full-text available
Lakes provide many important benefits to society, including drinking water, flood attenuation, nutrition, and recreation. Anthropogenic environmental changes may affect these benefits by altering lake water levels. However, background climate oscillations such as the El Niño–Southern Oscillation and the North Atlantic Oscillation can obscure long-term trends in water levels, creating uncertainty over the strength and ubiquity of anthropogenic effects on lakes. Here we account for the effects of background climate variation and test for long-term (1992–2019) trends in water levels in 200 globally distributed large lakes using satellite altimetry data. The median percentage of water level variation associated with background climate variation was 58 %, with an additional 10 % explained by seasonal variation and 25 % by the long-term trend. The relative influence of specific axes of background climate variation on water levels varied substantially across and within regions. After removing the effects of background climate variation on water levels, long-term water level trend estimates were lower (median: +0.8 cm yr−1) than calculated from raw water level data (median: +1.2 cm yr−1). However, the trends became more statistically significant in 86 % of lakes after removing the effects of background climate variation (the median p value of trends changed from 0.16 to 0.02). Thus, robust tests for long-term trends in lake water levels which may or may not be anthropogenic will require prior isolation and removal of the effects of background climate variation. Our findings suggest that background climate variation often masks long-term trends in environmental variables but can be accounted for through more comprehensive statistical analyses.
... The large-scale atmospheric circulation can influence regional climate by teleconnection to further perturb runoff (Li et al., 2011;Sharma et al., 2020;Tan et al., 2016;Wang and Zhou, 2007). As runoff is simultaneously affected by multiple regional and global environmental factors (Hidalgo and Dracup, 2003;Verdon et al., 2004), the combined effects of multiple factors and their interactions on runoff should be considered (Gorguner et al., 2019;Li and Jin, 2017;Ning et al., 2016;Oshima et al., 2015). ...
... It directly affects rainfall distribution in the tropics and can have a strong influence on weather across the world (Jury et al., 2007;Yeh et al., 2009). The effects of ENSO are strongly influenced by PDO (Goodrich, 2007;Hidalgo and Dracup, 2003). The ENSO events can be enhanced/reduced if the two indicators are in the same/different phase(s) (Stuecker, 2018). ...
Article
The limited runoff in cold and arid regions is sensitive to environmental changes, and it is thus urgent to explore the change and controlling factors of runoff under the background of global warming and intensified human activities. However, previous studies have rarely considered the combined effects of multiple controlling factors at varying scales over time. With the headwater region of the Manas River in northwest China as the study area, we investigated the change in runoff for the period of 1954–2016 and its relationship with regional environmental factors (e.g. precipitation PCP, temperature TMP, potential evapotranspiration ET0, snow cover extent SCE, land use, and normalized difference vegetation index NDVI) and/or global atmospheric circulation (e.g. North Atlantic Oscillation NAO, Arctic Oscillation AO, Pacific Interdecadal Oscillation PDO, and El Nino Southern Oscillation ENSO). In particular, the combined effects of multiple environmental factors were determined at different scales by the multiple wavelet coherence. The annual runoff significantly increased at a rate of 0.508 × 10⁸ m³/decade, and the climate tended to be warmer and wetter. Among the regional and global environmental factors, NDVI and ENSO were the single factor mostly correlated with runoff, while NDVI-TMP and ENSO-PDO were the combined factors with the stronger relations on runoff, respectively. The regional environmental factors had larger impacts on runoff than the global environmental factors, and the natural factors outperformed human activities in controlling runoff. The accelerated melting of snow/glacier induced by the increasing temperature dominated runoff change, and the increasing water inputs from wetter climate may play a second role in runoff. The runoff characteristics in cold and arid regions seem to be different from those regions with little snow/glacier, which should be paid more attention. The employed multiple wavelet coherence is helpful in determining the processes dominating runoff change.
... Climate indices, in particular El Niño-Southern Oscillation (ENSO) (Mason and Goddard, 2001), have been conventionally used in precipitation forecasting (Hamlet and Lettenmaier, 1999;Hidalgo and Dracup, 2003;Peel et al., 2004). Teleconnections with climate indices generally reflect slowly varying and recurrent components, such as sea surface temperature (SST), of atmospheric circulations that associate with climate anomalies over large distances in both the tropics and extratropics (Webster and Yang, 1992;Mason and Goddard, 2001;Lim et al., 2021). ...
... As one of the most remarkable teleconnections, ENSO affects the global climate through eastward-propagating Kelvin waves, westward-propagating Rossby waves and Walker circulations that span the tropical Pacific, Indian and Atlantic oceans (Yang et al., 2018;Webster and Yang, 1992). For regions exhibiting teleconnection patterns, various forecasting models have been developed, including historical resampling methods (Hamlet and Lettenmaier, 1999;Wood and Lettenmaier, 2006;Lim et al., 2021), statistical and Bayesian methods (Hidalgo and Dracup, 2003;Strazzo et al., 2019;Emerton et al., 2017) and machine-learning methods (L. Xu et al., 2020;Li et al., 2021). ...
Article
Full-text available
While El Niño–Southern Oscillation (ENSO) teleconnection has long been used in statistical precipitation forecasting, global climate models (GCMs) provide increasingly available dynamical precipitation forecasts for hydrological modeling and water resources management. It is not yet known to what extent dynamical GCM forecasts provide new information compared to statistical teleconnection. This paper develops a novel set operations of coefficients of determination (SOCD) method to explicitly quantify the overlapping and differing information for GCM forecasts and ENSO teleconnection. Specifically, the intersection operation of the coefficient of determination derives the overlapping information for GCM forecasts and the Niño3.4 index, and then the difference operation determines the differing information in GCM forecasts (Niño3.4 index) from the Niño3.4 index (GCM forecasts). A case study is devised for the Climate Forecast System version 2 (CFSv2) seasonal forecasts of global precipitation in December–January–February. The results show that the overlapping information for GCM forecasts and the Niño3.4 index is significant for 34.94 % of the global land grid cells, that the differing information in GCM forecasts from the Niño3.4 index is significant for 31.18 % of the grid cells and that the differing information in the Niño3.4 index from GCM forecasts is significant for 11.37 % of the grid cells. These results confirm the effectiveness of GCMs in capturing the ENSO-related variability of global precipitation and illustrate where there is room for improvement of GCM forecasts. Furthermore, the bootstrapping significance tests of the three types of information facilitate in total eight patterns to disentangle the close but divergent associations of GCM forecast correlation skill with ENSO teleconnection.
... Thus, it can be concluded that the shift observed in the streamflow stations was due to the impact of El Niño coupled with warm and cold phases of PDO. This agrees with several studies indicating that the hydro-climatology in the CRB was complex, and that no single climate index could be used to explain the entire temporal and spatial variability within the basin (Hidalgo and Dracup 2003, McCabe et al. 2007, Sagarika et al. 2015. ...
Article
This study evaluates changes in streamflow, temperature and precipitation over a time span of 105 years (1906-2010) in the Colorado River Basin (CRB). Monthly precipitation and temperature data for 29 climate divisions, and streamflow data for 29 naturalized gauges were analyzed. Two variations of the Mann-Kendall test, considering lag-1 auto-correlation and long-term persistence, and the Pettitt test were employed to assess trends and shifts, respectively. Results indicated that streamflow increased during winter-spring months and decreased during summer–fall periods. Decreasing trends in winter precipitation were identified over snow-dominated regions in the upper basin. Significant increase in temperature was detected over several months. Major shifts were noticed in 1964, 1968 and in the late 1920s. Increasing temperature while decreasing streamflow and precipitation were noticed after major shift in the 1930s and these shifts coincided with coupled phases of El Niño Southern Oscillation and Pacific Decadal Oscillation switching from cool to warm phase.
... As an index of the ENSO-like variability on the interdecadal time scale, Mantua et al. (1997) defined the Pacific decadal oscillation (PDO), the leading principal component (PC) of the monthly mean SST departure from the globally averaged SST (SST*) field over the Pacific sector in the domain poleward of 208N. The PDO has been widely used in studies of El Niño impacts, often in combination with ENSO indices based on SST anomalies in the equatorial Pacific cold tongue region (Miles et al. 2000;Papineau 2001;Hidalgo and Dracup 2003;Hamlet et al. 2005;Chan and Zhou 2005;Schoennagel et al. 2005;Pavia et al. 2006;Roy 2006;Yu et al. 2007). Though it is based entirely upon the extratropical Northern Hemisphere SST field, the PDO index has proven to be a useful indicator of ENSO-like interdecadal variability throughout the Pacific basin. ...
Article
A framework for interpreting the Pacific decadal oscillation (PDO) and ENSO indices is presented. The two leading principal components (PCs) of sea surface temperature [SST; strictly speaking, the departure from globally averaged SST (SST*)] over the entire Pacific basin comprise a two-dimensional phase space. A linear combination of these pan-Pacific PCs corresponding to a +45 degrees rotation (designated by P) is nearly identical to the PDO, the leading PC of Pacific SST* poleward of 20 degrees N. Both P and the PDO index exhibit apparent "regime shifts'' on the interdecadal time scale. The orthogonal axis (rotated by -45 degrees and designated by T') is highly correlated with conventional ENSO indices, but its spatial regression pattern is more equatorially focused. SST variability along these two rotated axes exhibits sharply contrasting power spectra, the former (i.e., P) suggestive of "red noise'' on time scales longer than a decade and the latter (i.e., T') exhibiting a prominent spectral peak around 3-5 years. Hence, orthogonal indices representative of the ENSO cycle and ENSO-like decadal variability can be generated without resorting to filtering in the time domain. The methodology used here is the same as that used by Takahashi et al. to quantify the diversity of equatorial SST patterns in ENSO; they rotated the two leading EOFs of tropical Pacific SST, whereas the two leading EOFs of pan-Pacific SST* are rotated here.
... Mexico, and Arizona ( Figure 1). (Iorns et al. 1965;Van Steeter and Pitlick 1998;Hidalgo and Dracup 2003). ...
Technical Report
Full-text available
Status and trajectory of an animal population depends on its demographic rates, and endangered species management, in particular, relies on such quantifiable population descriptors to guide the recovery process. Recovery goals for federally endangered razorback sucker Xyrauchen texanus (Abbott), family Catostomidae, require that two ―genetically and demographically viable, self-sustaining‖ adult populations, each exceeding 5,800 individuals, exist in the Upper Colorado River Basin before downlisting or delisting can occur. Current wild populations are so depleted that the first management action to achieve recovery is to reestablish populations with hatchery-produced fish. An integrated stocking plan was implemented in 2003 and stocking goals initiated in 2004 call for 9,930 age-2 (≥ 300 mm TL) individuals to be stocked in each of the middle Green River and upper Colorado River subbasins for each of six consecutive years, thus creating the presumptive recovery populations which must become self-sustaining to meet recovery goals. The stocking plan assumes annual survival rates of 50% for age-2 fish, 60% for age-3 fish, and 70% for adult (≥ age-4) fish. We used tag recapture data to estimate apparent survival, φ, and capture probability, p, for 96,448 hatchery-reared razorback suckers stocked into Upper Colorado River Basin streams, 2004–2007. Annual recapture data included 1,511 recapture events of 1,470 individuals from 2005–2008. We investigated the following effects: rearing method, reach, year, and season of stocking, fish total length (TL) at time of stocking, and first year in the river after stocking versus subsequent years. Mean first-year survival rates for razorback suckers of average TL (301.5 mm) stocked from 2005–2007 were low for fish reared by all methods: 0.03, 0.05, and 0.08 for tank-, pond-, and intensively (combination of indoor tank and outdoor pond)-reared fish, respectively. Rates were higher in the 2004–2005 interval for pond-reared (0.20) and intensively-reared (0.27) razorback suckers; no tank-reared fish were stocked that year. Total length at stocking and 1st-year survival were positively correlated; survival of fish (reared by any method) smaller than 200 mm TL approached zero but increased to an average of 0.83 for the few fish larger than 500 mm TL. Mean 1st-year survival of razorback suckers of average total length at stocking (301.5 mm) was 0.09. Season of stocking had a large effect on razorback sucker 1st-year survival rate estimates. Mean rates for razorback suckers of average TL (301.5 mm) stocked during summer were 0.03, 0.03, and 0.04 for tank-, pond-, and intensively-reared fish, respectively. Stocking during spring produced the highest mean estimates: 0.20, and 0.29 for pond-, and intensively-reared fish, respectively. Only five tank-reared razorback suckers were stocked during spring, none of which were recaptured during the study period. Effects of tank-rearing and summer-stocking could not be distinguished, since nearly all tank-reared fish (94%) were stocked during summer months. However, the adverse effect of stocking during summer was demonstrated by similar, low 1st-interval survival of fish reared by other methods. Furthermore, proportions of summer-stocked individuals subsequently recaptured were 0.5% or lower for pond- and intensively-reared razorback suckers. Tank- and pond-reared razorback suckers had higher predicted 1st-interval survival when stocked into the lower Green River reach (GR1) than Colorado or Gunnison River reaches. Survival of intensively-reared fish did not differ among the Green River reaches. Comparisons among all rearing methods within reach GR1 were not possible due to imbalance of numbers stocked there per method and year. Survival rates for razorback suckers after their first intervals in the river were high: 0.75–0.94, depending on interval and rearing method. Capture probabilities were all low, ranging from an average of 0.10 for a fish (reared by any method) on its first occasion in the river after stocking down to 0.02 on subsequent occasions. Pond-reared razorback suckers were captured in the highest proportion (68% of all recaptures) and had the highest predicted recapture probabilities (0.11–0.31), when averaging across reaches and years of stocking. Maintenance of self-sustaining populations is the underlying goal of all razorback sucker recovery efforts. Our results suggest that stocking fish larger than the currently recommended 300 mm TL in seasons other than summer would aid in accomplishing that goal. A cost-benefit analysis of hatchery production and stocking strategies is necessary to determine the trade-offs of raising fewer, larger razorback suckers with higher survival rates versus many, smaller fish with lower survival. Techniques to improve 1st-interval survival, including exercise conditioning and predator-avoidance training, should be investigated further. A comprehensive razorback sucker monitoring program, which includes early life stages as well as adults, would assist with increasing recapture probabilities. Employing a standardized stocking protocol would allow better estimation of the effects of certain important variables, such as rearing methods. Implementation of management strategies derived from these post-stocking survival rate estimates will immediately enhance recovery prospects for razorback sucker in the Upper Colorado River Basin.
... It is well accepted that some major climatic oscillations have large impacts on the multiperiodic variations of the precipitation at global and regional scales (Dai and Wigley, 2000;New et al., 2001;Wu et al., 2003;Deflorio et al., 2013;Ouyang et al., 2014;Gu and Adler, 2015;Xiao et al., 2015). As the most prominent natural interannual signal in the tropical Pacific, El Niño-Southern Oscillation (ENSO) plays important roles on the variability, magnitude, and distributions of regional and global precipitation due to the ocean-atmosphere interactions (Hidalgo and Dracup, 2003;Wu et al., 2003;McPhaden et al., 2006;Yeh et al., 2009;Hu and Huang, 2009;Qian et al., 2011;Power et al., 2013;Ouyang et al., 2014;Zhang et al., 2014;Huang et al., 2016;Hu et al., 2017;Infanti and Kirtman, 2016). As a long lived El Niño-like pattern of Pacific climate variability (Zhang et al., 1997;Minobe, 1999;Wang et al., 2014;Bo and Dai, 2015), Pacific Decadal Oscillation (PDO) is also important modulator of interdecadal/multi-decadal precipitation changes at middle to high latitudes in Northern Hemisphere (Hurrell, 1995;Mantua et al., 1997;Ma, 2007;Hu et al., 2013;Gu and Adler, 2015). ...
Article
Full-text available
This study examines the temporal variations and spatial distributions of annual precipitation over Central Asia during the periods of 1901–2013, 1951–2013, and 1979–2013 using the latest version of Global Precipitation Climatology Centre (GPCC) full data reanalysis version 7 (GPCC V7) data set. The linear trend and multiperiods of the precipitation over the entire region and plain and mountainous area separately are analysed by linear least square method and ensemble empiricalmode decompositionmethod. An overall increasing trend [0.66mm(10 years)−1] is found for the entire region during 1901–2013, which is smaller than that of 1951–2013. The regional annual precipitation exhibits multi-decadal variations, with a sharp decline during 1901–1944, followed by an increase until 1980s, and a fluctuation thereafter. During 1979–2013, the mountainous area shows a greater increasing trend than the entire region. Furthermore, the regional annual precipitation has exhibited high-frequency variations with 3-year and 6-year quasiperiods and a low-frequency variation with 28-year quasiperiods. In terms of the spatial distribution, increasing trend in the annual precipitation is found in Xinjiang and decreasing trends appear over the five countries of Central Asia during 1951–2013. Empirical orthogonal function results show that the mountainous area is the large variability centre of the annual precipitation. The dominant mode of interannual variability in Central Asia annual precipitation is related to El Niño-Southern Oscillation, which explains about 17% of the interannual variance during 1951–2013. The results of this study describe the long-term variation in the annual precipitation over Central Asia as well as its relationship with some key climate indices in great detail, which will benefit the understanding and the prediction of the climate variations in this region.
... The ENSO cycle has been linked to annual worldwide weather patterns called teleconnections. ENSO patterns have been implicated in drying trends in Tanzania (Harrison et al. 2019) and precipitation in the Colorado River Basin (Hidalgo and Dracup 2003), East Africa (Indeje et al. 2000;Phillips and McIntyre 2000), Israel (Price et al. 1998), and elsewhere (Glantz 2002;Knippertz et al. 2003). Both temperature and precipitation are related to ENSO patterns in Mexico (Pavia et al. 2006). ...
Article
Full-text available
Distinctive annual weather patterns in the Western Kenya Highlands have been attributed to El Niño Southern Oscillation (ENSO) teleconnections. A novel application of a recently developed analytical approach is used to identify statistically significant differences between temperature and rainfall patterns in the Kakamega District during the El Niño and La Niña periods of the ENSO cycle. This approach separates the seasonal trend and 1-day autocorrelation from the statistical noise in an annual data set. The standard deviation of this noise is further analyzed for its own seasonal trend. Thirty-eight years of reanalysis data are analyzed, and statistical comparisons are made on all three aspects of this analysis. El Niño years were characterized by a phase shift in temperature patterns. Larger random variation was detected in El Niño years during the long rains than in La Niña years, leading to a higher probability of anomalously high rainfall. Larger random variation was detected in La Niña years during the short rains, leading to both a higher probability of anomalously high rainfall and a higher probability of no rainfall. The method appears to be a promising tool for analyzing not only the effects of distant teleconnections but also the nature of those effects.
... Here, several studies have indeed found strong relationships between ENSO and annual or seasonal discharge (e.g. Hidalgo and Dracup, 2003;Piechota et al., 1997) or between ENSO and drought conditions (Piechota and Dracup, 5 1996). Generally, these studies found wetter conditions in El Niño years and drier conditions in La Niña years. ...
Article
Full-text available
Floods are amongst the most dangerous natural hazards in terms of economic damage. Whilst a growing number of studies have examined how river floods are influenced by climate change, the role of natural modes of interannual climate variability remains poorly understood. Here, we present the first global assessment of the influence of El Niño Southern Oscillation (ENSO) on river floods. The analysis was carried out by simulating daily gridded discharges using the WaterGAP model, and examining statistical relationships between these discharges and ENSO indices. We found that, over the period 1958–1999, ENSO exerted a significant influence on annual floods in river basins covering over a third of the world's land surface, and that its influence on floods has been much greater than its influence on average flows. We show that there are more areas in which annual floods intensify with La Niña and decline with El Niño than vice versa. However, we also found that in many regions the strength of the relationships between ENSO and annual floods have been non-stationary, with either strengthening or weakening trends during the study period. We discuss the implications of these findings for science and management. Given the strong relationships between ENSO and annual floods, we suggest that more research is needed to assess relationships between ENSO and flood impacts (e.g. loss of lives or economic damage). Moreover, we suggest that in those regions where useful relationships exist, this information could be combined with ongoing advances in ENSO prediction research, in order to provide year-to-year probabilistic flood risk forecasts.
... In previous studies, ENSO has been identified as a major factor affecting the atmospheric anomalies (extreme conditions) both globally and regionally (Ropelewski and Halpert 1986;Kahya and Dracup, 1993). Studies have found PDO to have an influence on such parameters as snowpack formation, precipitation, and streamflow in the western United States, especially in such regions as the Colorado River Basin and California (Dettinger and Cayan 1995;Hidalgo and Dracup 2003;Cañón et al. 2007;Sagarika et al., 2015a). Besides understanding the relationship between ENSO and PDO with the various hydrologic parameters, many studies have focused on understanding the coupling effect of ENSO and PDO. ...
Article
Full-text available
This study investigated the correlation between western US streamflow and two of the most important oceanic–atmospheric indices having significant effects in this region, namely, El Niño Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO). Data from 61 streamflow stations across six different hydrologic regions of the western USA were analyzed, using a study period of 60 years from 1951 to 2010. Continuous wavelet transformation along with cross wavelet transformation and wavelet coherence were used to analyze the interaction between streamflow and climate indices. The results showed that streamflows have changed coincidentally with both ENSO and PDO over the study period at different time-scale bands and at various time intervals. Both ENSO and PDO showed correlation with streamflow change behavior from 1980 to 2005. ENSO showed a strong correlation with streamflow across the entire study period in the 10–12 year band. PDO showed a strong correlation in bands of 8–10 years and bands beyond 16 years. The phase relationship showed that both ENSO and PDO preceded streamflow change behavior; in some instances, the variables were found to be moving in opposite directions even though they changed simultaneously. The results can be helpful in understanding the relationship between the climate indices and streamflow.
... The proposed hybrid approach benefits from the predictability of an analog-year model based on teleconnection indices [Hidalgo and Dracup, 2003; Kurtzman and Scanlon, 2007]. We propose a Bayesian model based on copula functions [Joe, 1997; Nelsen, 1999] to represent the joint distribution of teleconnection indices and seasonal precipitation. ...
Article
Improving water management in water stressed-regions requires reliable seasonal precipitation predication, which remains a grand challenge. Numerous statistical and dynamical model simulations have been developed for predicting precipitation. However, both types of models offer limited seasonal predictability. This study outlines a hybrid statistical-dynamical modeling framework for predicting seasonal precipitation. The dynamical component relies on the physically based North American Multi-Model Ensemble (NMME) model simulations (99 ensemble members). The statistical component relies on a multivariate Bayesian-based model that relates precipitation to atmosphere-ocean teleconnections (also known as an analog-year statistical model). Here the Pacific Decadal Oscillation (PDO), Multivariate ENSO Index (MEI), and Atlantic Multidecadal Oscillation (AMO) are used in the statistical component. The dynamical and statistical predictions are linked using the so-called Expert Advice algorithm, which offers an ensemble response (as an alternative to the ensemble mean). The latter part leads to the best precipitation prediction based on contributing statistical and dynamical ensembles. It combines the strength of physically based dynamical simulations and the capability of an analog-year model. An application of the framework in the southwestern United States, which has suffered from major droughts over the past decade, improves seasonal precipitation predictions (3-5 month lead time) by 5-60% relative to the NMME simulations. Overall, the hybrid framework performs better in predicting negative precipitation anomalies (10-60% improvement over NMME) than positive precipitation anomalies (5-25% improvement over NMME). The results indicate that the framework would likely improve our ability to predict droughts such as the 2012-2014 event in the western United States that resulted in significant socioeconomic impacts.
... Also since about the 1990s, a variety of stochastic forecasting approaches have been developed based on hydrologic, oceanic, and atmospheric predictors. It has demonstrated the significant effects of climatic signals such as SST, ENSO, PDO, AMO, and NAO and other atmospheric variables such as pressure and wind on precipitation and streamflow variations (e.g., [14,[306][307][308][309][310]) and that seasonal and longer-term streamflow forecasts can be improved using climatic factors (e.g., [307,[311][312][313][314][315]). ...
Chapter
Full-text available
Hydrology deals with the occurrence, movement, and storage of water in the earth system. Hydrologic science comprises understanding the underlying physical and stochastic processes involved and estimating the quantity and quality of water in the various phases and stores. The study of hydrology also includes quantifying the effects of such human interventions on the natural system at watershed, river basin, regional, country, continental, and global scales. The process of water circulating from precipitation in the atmosphere falling to the ground, traveling through a river basin (or through the entire earth system), and then evaporating back to the atmosphere is known as the hydrologic cycle. This introductory chapter includes seven subjects, namely, hydroclimatology, surface water hydrology, soil hydrology, glacier hydrology, watershed and river basin modeling, risk and uncertainty analysis, and data acquisition and information systems. The emphasis is on recent developments particularly on the role that atmospheric and climatic processes play in hydrology, the From: Handbook of Environmental Engineering, Volume 15: Modern Water Resources Engineering 1 advances in hydrologic modeling of watersheds, the experiences in applying statistical concepts and laws for dealing with risk and uncertainty and the challenges encountered in dealing with nonstationarity, and the use of newer technology (particularly spaceborne sensors) for detecting and estimating the various components of the hydrologic cycle such as precipitation, soil moisture, and evapotranspiration.
... The climate is typified by relatively cold winters and monsoonal summer precipitation (Adams andComrie 1997, Hereford et al. 2002). Precipitation varies widely between years and over multi-year periods; this variability is associated with the Pacific Decadal Oscillation and the El Niño-Southern Oscillation (Hidalgo and Dracup 2003). Climate also varies spatially across the Colorado Plateau, with mean annual temperatures and precipitation ranging from 2°to 23°C and 80-600 mm, respectively 1900-2014Menne et al. 2015), and a gradient in summer monsoon precipitation from the south/ southeast to the north/northwest. ...
Article
Full-text available
The combination of co-occurring climate change and increasing land-use is likely to affect future environmental and socioeconomic conditions in drylands; these hyper-arid to sub-humid landscapes are limited by water resources and prone to land degradation. We characterized the potential for geographic overlap among land-use practices and between land-use and climate change on the Colorado Plateau - a dryland region experiencing rapid changes in land-use and facing aridification. We characterized spatial patterns and temporal trends in aridification, land-use, and recreation at the county and 10-km² grid scales. Increasing trends and overlapping areas of high intensity for use, including oil and gas development and recreation, and climate drying, suggest areas with high potential to experience detrimental effects to the recreation economy, water availability, vegetation and wildlife habitat, and spiritual and cultural resources. Patterns of overlap in high-intensity land-use and climate drying differ from the past, indicating the potential for novel impacts and suggesting that land managers and planners may require new strategies to adapt to changing conditions. This analytical framework for assessing the potential impacts of overlapping land-use and climate change could be applied with other drivers of change or to other regions to create scenarios at various spatial scales in support of natural resource planning efforts.
... As a result, scientists have been trying the best to figure out what has caused the severe drought. Most recent analysis and forecasting about west U.S. drought have focused on the Pacific Ocean to find reasons, specifically on oceanic patterns such as the El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) [4][5][6][7] . For instance, it has been found that the La Niña events can bring dry conditions to the west United States, especially when PDO is in its negative phase, the teleconnections between La Niña and the west U.S. drought tend to be strong and stable. ...
Article
Full-text available
In this study, relations between winter-time Pacific-Northern America pattern (PNA)/East Pacific wave-train (EPW) and winter-time drought in the west United States over the period of 1951–2010 are analyzed. Considering traditional Pearson’s Correlation Coefficient can be influenced by non-stationarity and nonlinearity, a recently proposed method, Detrended Partial-Cross-Correlation Analysis (DPCCA) is applied. With DPCCA, we analyzed the “intrinsic” correlations between PNA/EPW and the winter drought with possible effects of ENSO and PDO removed. We found, i) significant negative correlations between PNA/EPW and drought on time scales of 5–6 years after removing the effects of ENSO, ii) and significant negative correlations between PNA/EPW and drought on time scales of 15–25 years after removing the effects of PDO. By further studying the temporal evolutions of the “intrinsic” correlations, we found on time scales of 5–6 years, the “intrinsic” correlations between PNA/EPW and drought can vary severely with time, but for most time, the correlations are negative. While on interdecadal (15–25 years) time scales, after the effects of PDO removed, unlike the relations between PNA and drought, the “intrinsic” correlations between EPW and drought takes nearly homogeneous-sign over the whole period, indicating a better model can be designed by using EPW.
... Interest in PDV arises from associated observed variations in seasonal climate in various regions of the globe. For example, the cold phase of PDV has been associated with an increased occurrence of drought in the western United States (Dai 2013;Hidalgo and Dracup 2003), southern China (Chan and Zhou 2005), central and southwestern Asia (Hoell et al. 2015;Lyon et al. 2013), and eastern Africa (Lyon 2014;Yang et al. 2014). Such tendencies have substantial implications for water resource management (e.g., Allen et al. 2014) and the energy and agricultural sectors (e.g., Swetnam and Betancourt 2010). ...
Article
Full-text available
Aglobal-scale decadal climate shift, beginning in 1998/99 and enduring through 2013, has been documented in recent studies, with associated precipitation shifts in key regions throughout the world. These precipitation shifts are most easily detected during March–May when ENSO effects are weak. Analyses have linked this climate shift to a shift in the Pacific decadal variability (PDV) pattern to its negative phase. Here the authors evaluate the predictive skill of the North American Multimodel Ensemble (NMME), and the CFSv2 model alone, in maintaining the observed precipitation shifts in seasonal forecasts, emphasizing the southwestern United States where deficient precipitation has tended to prevail since the late 1990s. The NMME hindcasts out to 6 months lead are found to maintain the observed decadal precipitation shifts in key locations qualitatively correctly, but with increasingly underestimated amplitude with increasing lead time. This finding holds in the separate CFSv2 model hindcasts. The decadal precipitation shift is relatively well reproduced in the southwestern United States. The general underestimation of the precipitation shift is suggested to be related to a muted reproduction of the observed shift in Pacific sea surface temperature (SST). This conclusion is supported by runs from a different (but overlapping) set of atmospheric models, which when forced with observed SST reproduce the decadal shifts quite well. Overall, the capability of the NMME model hindcasts to reflect the observed decadal rainfall pattern shift, but with weakened amplitude (especially at longer leads), underscores the broader challenge of retaining decadal signals in predictions of droughts and pluvials at seasonal-to-interannual time scales.
... For example, this fraction has increased at 75% of the weather stations in the western mountain ranges in the second half of the twentieth century (Field et al. 2007). Climate variability effects on hydroclimatic variations in Upper Colorado River Basin such as precipitation and streamflow have been investigated by Hidalgo and Dracup (2003). They found some relations between the Pacific Ocean and Upper Colorado River Basin climate as well as relations between the climate signals such as Pacific Decadal Oscillation (PDO) and El Niño Southern Oscillation (ENSO) with streamflow oscillations in the Upper Colorado River basin. ...
Article
Full-text available
A 1240-year-long record of reconstructed annual flows of the Colorado River at Lees Ferry is analysed using singular spectrum analysis and multi-taper method of spectral analysis. Spectral analysis of the 100-year-long recent record of annual flows of Colorado River in the measured and reconstructed forms shows similar oscillations in high- and low-frequency bands. Therefore, the oscillatory components and trends extracted from the reconstructed data are a good representative of inter-annual, multi-decadal, and multi-centennial variability of natural flow in the river. In Colorado River the length of flow data is 1240 years and multi-centennial and multi-decadal oscillatory components can be extracted at a high confidence level. In this research we attempt to find whether the changes in streamflow in the twentieth century are due to an external cause such as climate change or whether they are part of the natural variability of flow observed in the past. The results suggest that there is only a part of the linear trend, caused by climate change or man-made effects, and an important part of that is due to climate variability which is believed to be totally natural. The same line of climate variability is still acting on our planet, and it may have gained new aspects due to the change in atmospheric composition and circulation as a result of anthropogenic effects. This may cause serious limitations to the water sustainability and water availability on the earth. © 2015 International Association for Hydro-Environment Engineering and Research
... The opposite conditions result in wet periods (warm phases of ENSO, El Niño) and PDO (positive PDO, 1976-1999 and cool phase of AMO (negative AMO, 1964AMO, -1994 resulting in wet winters throughout much of 1980s and early 1990s. Although there is no consistent relationship between wet and dry conditions and climate cycles in the UCRB [Hidalgo and Dracup, 2003], the severe drought in the early 2000s and also in 2012 correspond to cool phases of ENSO (La Niña) and PDO and warm phase of AMO, as in the LCRB. The phases of the long-term climate Anthropogenic drivers of water storage change include water withdrawals, which are similar in the UCRB and LCRB (10 km 3 /yr) (Figures 2 and S11; Table S2). ...
Article
Full-text available
Use of GRACE (Gravity Recovery and Climate Experiment) satellites for assessing global water resources is rapidly expanding. Here we advance application of GRACE satellites by reconstructing long-term total water storage (TWS) changes from ground-based monitoring and modeling data. We applied the approach to the Colorado River Basin which has experienced multiyear intense droughts at decadal intervals. Estimated TWS declined by 94 km3 during 1986-1990 and by 102 km3 during 1998-2004, similar to the TWS depletion recorded by GRACE (47 km3) during 2010-2013. Our analysis indicates that TWS depletion is dominated by reductions in surface reservoir and soil moisture storage in the upper Colorado basin with additional reductions in groundwater storage in the lower basin. Groundwater storage changes are controlled mostly by natural responses to wet and dry cycles and irrigation pumping outside of Colorado River delivery zones based on ground-based water level and gravity data. Water storage changes are controlled primarily by variable water inputs in response to wet and dry cycles rather than increasing water use. Surface reservoir storage buffers supply variability with current reservoir storage representing ∼2.5 years of available water use. This study can be used as a template showing how to extend short-term GRACE TWS records and using all available data on storage components of TWS to interpret GRACE data, especially within the context of droughts.
... Seasonal to annual hydroclimatic predictions have been improved recently based on ocean-atmosphere teleconnection mechanisms such as El Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) (Hidalgo and Dracup 2003;Bracken et al. 2010;Sankarasubramanian et al. 2008;Switanek et al. 2009). Benefiting from this advancement, climate-related impact research institutes have been able to make better seasonal forecasts for climatic variables such as temperature and precipitation (Saha et al. 2006; Barnston et al. 2011;Held et al. 2005). ...
Article
Full-text available
We investigate how to identify and assess teleconnection signals between anomalous patterns of sea surface temperature (SST) changes and climate variables related to hydrologic impacts over different river basins. The regional climate sensitivity to tropical SST anomaly patterns is examined through a linear relationship given by the global teleconnection operator (GTO, also generally called a sensitivity matrix or an empirical Green’s function). We assume that the GTO defines a multilinear relation between SST forcing and regional climate response of a target area. The sensitivities are computed based on data from a large ensemble of simulations using the NCAR Community Atmospheric Model version 3.1 (CAM 3.1). The linear approximation is evaluated by comparing the linearly reconstructed response with both the results from the full non-linear atmospheric model and observational data. The results show that the linear approximation can capture regional climate variability that the CAM 3.1 AMIP-style simulations produce at seasonal scales for multiple river basins. The linear method can be used potentially for estimating drought conditions, river flow forecasting, and agricultural water management problems.
... The current study explores the suitability of the MODIS-PET product for use in hydrologic studies in the Upper Colorado River Basin (UCRB). The UCRB supplies 85-90% of water to the Colorado River, on average, serving over 30 million people across the southwest (Hidalgo and Dracup 2003, Christensen and Lettenmaier 2007, Painter et al. 2012. Regional drought and forest disturbance are impacting water supply across the basin (Claessens et al. 2006, McCabe andWolock 2007), increasing the need for improved temporal and spatial data to better quantify regional variability in hydrologic fluxes (Smith and Kummerow 2013;Singh et al. 2013). ...
Article
This study evaluates a remotely sensed and two ground-based potential evapotranspiration (PET) products for hydrologic application in the Upper Colorado River Basin (UCRB). The remotely sensed Moderate Resolution Imaging Spectroradiometer product (MODIS-PET) is a continuous, daily time series with 250 m resolution derived using the Priestley-Taylor (P-T) equation. The MODIS-PET is evaluated against regional flux tower data as well as a synthetic pan product (Epan; 0.125°, daily) derived from the North American Land Data Assimilation System (NLDAS) and a Hargreaves PET derived from DAYMET variables (DAYMET-PET; 1 km, daily). Compared to point-scale PET computed using regional flux tower data, the MODIS-PET had lower errors, with RMSE values ranging from 2.24 to 2.85 mm/day. Epan RMSE values ranged from 3.70 to 3.76 mm/day and DAYMET-PET RMSE values ranged from 3.55 to 4.58 mm/day. Further investigation showed biases in temperature and radiation data contribute to uncertainty in the MODIS-PET values, while bias in NLDAS temperature, downward shortwave (SW↓), and downward longwave (LW↓) propagate in the Epan estimates. Larger discrepancies between methods were observed in the warmer, drier regions of the UCRB, however, the MODIS-PET was more responsive to landcover transitions and better captured basin heterogeneity. Results indicate the satellite-based MODIS product can serve as a viable option for obtaining spatial PET values across the UCRB.
... Therefore, relevant information of ENSO and PDO would cause improvements in precipitation and streamflow predictions, thereby mitigating floods and droughts in the Pacific region and elsewhere [19,20]. Since the influences of ENSO and PDO have significant temporal variability [17,21], the value of using climate indices such as ENSO or PDO in water resource predictions depends on understanding of the local relationship between these indices and hydrological factors on time [17]. ...
Article
Full-text available
Profiling the hydrological response of watershed precipitation and streamflow to large-scale circulation patterns and astronomical factors provides novel information into the scientific management and prediction of regional water resources. Possible contacts of El Niño–Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), sunspot activity to precipitation and streamflow in the upper Yangtze River basin (UYRB) were investigated in this work. Monthly precipitation and streamflow were utilized as well as contemporaneous same-scale teleconnections time series spanning a total of 70 years from 1951 to 2020 in precipitation and 121 years from 1900 to 2020 in streamflow. The principal component analysis (PCA) method was applied so as to characterize the dominant variability patterns over UYRB precipitation time series, with the temporal variability of first two modes explaining more than 80% of total variance. Long-term evolutionary pattern and periodic variation characteristics of precipitation and streamflow are explored by applying continuous wavelet transform (CWT), cross-wavelet transform (XWT) and wavelet coherence (WTC), analyzing multi-scale correlation between hydrological variables and teleconnections in the time-frequency domain. The results manifest that ENSO exhibits multiple interannual period resonance with precipitation and streamflow, while correlations are unstable in time and phase. PDO and sunspot effects on precipitation and streamflow at interannual scales vary with time-frequency domains, yet significant differences are exhibited in their effects at interdecadal scales. PDO exhibits a steady negative correlation with streamflow on interdecadal scales of approximately 10 years, while the effect of sunspot on streamflow exhibits extremely steady positive correlation on longer interdecadal scales of approximately 36 years. Analysis reveals that both PDO and sunspot have significantly stronger effects on streamflow variability than precipitation, which might be associated with the high spatiotemporal variability of precipitation.
... Studies suggest that both ENSO and PDO have worked as influencing factors to alter the western US hydrology, especially in the Colorado River Basin (CRB) and California region (Kahya and Dracup, 1993;Hidalgo and Dracup, 2003;Sagarika et al., 2015a;Pathak et al., 2016a). The recent droughts in California have drawn the attention of many climate researchers (Griffin and Anchukaitis, 2014;Wei et al., 2016). ...
Conference Paper
Full-text available
El Niño Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) are two of the most important climate indices that influence the western U.S. hydrology significantly. This study evaluated how these two indices have influenced California streamflow over the years and determined their correlation at multiple time-scales. Data were obtained from 14 unimpaired streamflow stations of California for a study period of 63 years (i.e., 1951 to 2013). The concept of continuous wavelet transform was applied to observe the variance in each time-series at multiple time-scale bands over the years. The correlation was found to be higher in the latter half of the study period. ENSO showed a higher correlation with California streamflow compared to PDO across the study period. The results of this study can be of assistance in determining the relationship between Pacific SST fluctuation and California streamflow. The findings may help understand the recent California drought as well.
... Ocean-atmosphere interactions are known for regulating global energy flow that influences rainfall amounts and distribution on a regional scale [1][2][3]. The link between these drivers, rainfall pattern, and general hydroclimate variability has been a focus of several studies on a regional scale [2,[4][5][6][7][8][9][10]. For example, the magnitude, spatial, and temporal distribution of rainfall in the United States are a function of different modes of ocean-atmosphere interaction processes, as well as other global and regional conditions. ...
Article
Full-text available
Drought variability is associated with global oceanic and atmospheric teleconnections driven by, among others, the Pacific Decadal Oscillation (PDO), the Atlantic Multidecadal Oscillation (AMO), and El Niño–Southern Oscillation (ENSO). Climate teleconnections with a region’s rainfall, with drought and flooding implications, should be part of short- and long-term water management planning and operations. In this study, the link between drought and climatic drivers was assessed by using historical data from 110 years of regional rainfall in southern Florida and the Everglades. The objective was to evaluate historical drought and its link with global oceanic and atmospheric teleconnections. The Standardized Precipitation Index (SPI) assesses regional historical drought in 3-, 6-, 12-, 24-, 36-, 48-, and 60-month periods. Each of the SPIs was used to analyze the association of different magnitudes of drought with ENSO, AMO, and PDO. Historical drought evaluated in different time windows indicated that there is a wet and dry cycle in the regional hydrology, where the area is currently in the wet phase of the fluctuation since 1995 with some drought years in between. Regional historical rainfall anomaly and drought index relationships with each driver and combination of drivers were statistically evaluated. The impact of ENSO fluctuation is limited to short-period rainfall variability, whereas long-period influence is from AMO and PDO.
... In previous studies, ENSO has been identified as a major factor affecting the atmospheric anomalies (extreme conditions) both globally and regionally (Ropelewski and Halpert, 1986;Kahya and Dracup, 1993). Studies have found PDO to have an influence on such parameters as snowpack formation, precipitation, and streamflow in the western U.S., especially in such regions as the Colorado River Basin (CRB) and California (Dettinger and Cayan, 1995;Hidalgo and Dracup, 2003;Cañón et al., 2007;Sagarika et al., 2015a Kalra and Ahmad (2012) concluded that climate signals significantly influenced annual precipitation behavior in the CRB; ...
... Consequently, long climate records or proxies are needed to extend streamflow data to get insights as to how water supply variability is manifest over long periods of time. For instance, streamflow responds to large-scale atmospheric teleconnection patterns of both high and low frequency (Cayan et al., 1999;Hamlet & Lettenmaier, 2000;Hidalgo & Dracup, 2003;Najibi et al., 2017;Nowak et al., 2012;Redmond & Koch, 1991;Wise et al., 2018). Shorter streamflow records may not be representative of longer-term variability in streamflow even with typical stochastic simulation methods that use the recorded data. ...
Article
Full-text available
A Bayesian model that uses the spatial dependence induced by the river network topology, and the leading principal components of regional tree ring chronologies for paleo‐streamflow reconstruction is presented. In any river basin, a convergent, dendritic network of tributaries come together to form the main stem of a river. Consequently, it is natural to think of a spatial Markov process that recognizes this topological structure to develop a spatially consistent basin‐scale streamflow reconstruction model that uses the information in streamflow and tree ring chronology data to inform the reconstructed flows, while maintaining the space‐time correlation structure of flows that is critical for water resource assessments and management. Given historical data from multiple streamflow gauges along a river, their tributaries in a watershed, and regional tree ring chronologies, the model is fit and used to simultaneously reconstruct the full network of paleo‐streamflow at all gauges in the basin progressing upstream to downstream along the river. Our application to 18 streamflow gauges in the Upper Missouri River Basin shows that the mean adjusted R2 for the basin is approximately 0.5 with good overall cross‐validated skill as measured by five different skill metrics. The spatial network structure produced a substantial reduction in the uncertainty associated with paleo‐streamflow as one proceeds downstream in the network aggregating information from upstream gauges and tree ring chronologies. Uncertainty was reduced by more than 50% at six gauges, between 6% and 50% at one gauge, and by less than 5% at the remaining 11 gauges when compared with the traditional principal component regression reconstruction model.
... The SST in the Pacific Ocean from 20°N to poleward has ENSO-like pattern with a significant impact on wind pattern in the Northern Pacific Ocean (Hidalgo and Dracup, 2003;McCabe et al., 2004;Pavia et al., 2006;Oglesby et al., 2012). During a PDO warm phase, the central and western Pacific SST becomes less than normal and the eastern portion greater than normal. ...
... Although the scope of such studies varies, there is generally a consistent theme of exploring the change in temporal behaviours at different locations in space. One feature of particular interest to hydrology researchers has been streamflow modelling [31,32], where a significant amount of work has focused on modelling regional locations across the United States [33,34,35,36,37]. Many of these studies have taken a more concentrated approach, providing detailed analysis on relatively few hydrology stations. ...
Preprint
Full-text available
We use new and established methodologies in multivariate time series analysis to study the dynamics of 414 Australian hydrological stations' streamflow. First, we analyze our collection of time series in the temporal domain, and compare the similarity in hydrological stations' candidate trajectories. Then, we introduce a Whittle Likelihood-based optimization framework to study the collective similarity in periodic phenomena among our collection of stations. Having identified noteworthy similarity in the temporal and spectral domains, we introduce an algorithmic procedure to estimate a governing hydrological streamflow process across Australia. To determine the stability of such behaviours over time, we then study the evolution of the governing dynamics and underlying time series with time-varying applications of principal components analysis (PCA) and spectral analysis.
... One issue with hydrological applications of GCMs or coupled RCM-GCMs, is that they do not appropriately capture hydrologically important climate processes (i.e., El Niño) and structures (e.g., Robertson and Mechoso 1998;Wang et al. 2006;Guilyardi et al. 2004;Ouachani et al. 2013). There are many studies that applied bias-corrected GCM and RCM outputs to examine changes in hydrology (e.g., Hidalgo and Dracup 2003;Wood et al. 2004;Teutschbein and Seibert 2012). Statistical downscaling of large-scale atmospheric circulations from GCMs to high-resolution variables at local scale is one widely used approach (e.g., Cannon 2008;Hsieh 2009;Maraun et al. 2010;Gaitan et al. 2014;Gutmann et al. 2014). ...
Article
Full-text available
How mountain hydrology at different elevations will respond to climate change is a challenging question of great importance to assessing changing water resources. Here, three North American Cordilleran snow-dominated basins—Wolf Creek, Yukon; Marmot Creek, Alberta; and Reynolds Mountain East, Idaho—each with good meteorological and hydrological records, were modeled using the physically based, spatially distributed Cold Regions Hydrological Model. Model performance was verified using field observations and found adequate for diagnostic analysis. To diagnose the effects of future climate, the monthly temperature and precipitation changes projected for the future by 11 regional climate models for the mid-twenty-first century were added to the observed meteorological time series. The modeled future was warmer and wetter, increasing the rainfall fraction of precipitation and shifting all three basins toward rainfall–runoff hydrology. This shift was largest at lower elevations and in the relatively warmer Reynolds Mountain East. In the warmer future, there was decreased blowing snow transport, snow interception and sublimation, peak snow accumulation, and melt rates, and increased evapotranspiration and the duration of the snow-free season. Annual runoff in these basins did not change despite precipitation increases, warming, and an increased prominence of rainfall over snowfall. Reduced snow sublimation offset reduced snowfall amounts, and increased evapotranspiration offset increased rainfall amounts. The hydrological uncertainty due to variation among climate models was greater than the predicted hydrological changes. While the results of this study can be used to assess the vulnerability and resiliency of water resources that are dependent on mountain snow, stakeholders and water managers must make decisions under considerable uncertainty, which this paper illustrates.
... Another approach is to look at physical processes when studying the Colorado River streamflows. The effects of El Niño-Southern Oscillation (ENSO), the Pacific decadal oscillation (PDO), and the Atlantic multidecadal oscillation (AMO) have been studied by various authors as they pertain to Colorado river streamflow (Nowak et al. 2012;Hidalgo and Dracup 2003;Redmond and Koch 1991). The results show that ENSO effects are more pronounced in the lower Colorado basin than the upper Colorado basin. ...
Article
Communities reliant upon the Colorado River system are at risk of water shortages because of fluctuations of the river's streamflows. The solution to the water supply problem for the Colorado River system lies within a quantitative understanding of these fluctuations during droughts. Streamflow data (direct and inferred) for the Colorado River extend back approximately 1200 years through the analysis of tree-ring records (Meko et al.; Woodhouse et al.). We further analyze these data using a mathematical model to present estimates for the future water supply of the Colorado River by comparing measured streamflows of the past century with the yearly tree-ring data of the Colorado River. We estimate that the Colorado River system's reservoirs lack enough stored water reserves to last through the current drought, which has been ongoing since 2000. If true, it is essential to reevaluate the way water is used and stored for the Colorado River. The methods presented are relevant to any river system whose streamflow statistics are Gaussian.
... Large-scale oceanic/atmospheric teleconnections such as the Atlantic Multi-decadal Oscillation (AMO), Pacific Decadal Oscillation (PDO), and El Niño-Southern Oscillation (ENSO) exhibit significant control over dominant storm tracks, precipitation, and resulting streamflow patterns across the western U.S. (Enfield et al., 2001;Hidalgo and Dracup, 2003;McCabe et al., 2004;Redmond and Koch, 1991). Our understanding of the long-term influence of multidecadal-scale climate variability on streamflow across the western U.S. is again relatively limited since most gage-based estimates of natural streamflow in the western U.S. often only capture one to three full cycles of these important decadal to multi-decadal climate drivers. ...
Article
Paleohydrologic records can provide unique, long-term perspectives on streamflow variability and hydroclimate for use in water resource planning. Such long-term records can also play a key role in placing both present day events and projected future conditions into a broader context than that offered by instrumental observations. However, relative to other major river basins across the western United States, a paucity of streamflow reconstructions has to date prevented the full application of such paleohydrologic information in the Upper Missouri River Basin. Here we utilize a set of naturalized streamflow records for the Upper Missouri and an expanded network of tree-ring records to reconstruct streamflow at thirty-one gaging locations across the major headwaters of the basin. The reconstructions explain an average of 68% of the variability in the observed streamflow records and extend available records of streamflow back to 886 CE on average. Basin-wide analyses suggest unprecedented hydroclimatic variability over the region during the Medieval period, similar to that observed in the Upper Colorado River Basin, and show considerable synchrony of persistent wet-dry phasing with the Colorado River over the last 1200 years. Streamflow estimates in individual sub-basins of the Upper Missouri demonstrate increased spatial variability in discharge during the Little Ice Age (∼1400–1850 CE) compared with the Medieval Climate Anomaly (∼800–1400 CE). The network of streamflow reconstructions presented here fills a major geographical void in paleohydrologic understanding and now allows for a long-term assessment of hydrological variability over the majority of the western U.S.
... As a result, the upper basin is colder and wetter than the lower basin: the mean annual temperature and precipitation are 4.5 C and 397 mm, respectively, in the upper basin, and 14.6 C and 328 mm in the lower basin. The inter-annual variability of precipitation in the CRB is high and partially controlled by teleconnections with the El Niño-Southern Oscillation (ENSO) (Hidalgo & Dracup, 2003). The CRB is a snowmelt-driven system where run-off is dominated by winter precipitation occurring mostly in form of snow in the upper basin (Kopytkovskiy, Geza, & McCray, 2015). ...
Article
The Colorado River basin (CRB) is the primary source of water in the southwestern United States. A key step to reduce the uncertainty of future streamflow projections in the CRB is to evaluate the performance of historical simulations of general circulation models (GCMs). In this study, this challenge is addressed by evaluating the ability of 19 GCMs from the Coupled Model Intercomparison Project Phase 5 (CMIP5) and four nested regional climate models (RCMs) in reproducing the statistical properties of the hydrologic cycle and temperature in the CRB. To capture the transition from snow-dominated to semi-arid regions, analyses are conducted by spatially averaging the climate variables in four nested sub-basins. Most models overestimate the mean annual precipitation (P) and underestimate the mean annual temperature (T) at all locations (up to +140% and -4.9 °C, respectively). A group of models capture the mean annual run-off at all sub-basins with different strengths of the hydrological cycle, depending on the level of P overestimation. Another set of models overestimate the mean annual run-off, due to a weak cycle in the evaporation channel. An abrupt increase in the mean annual T of ~0.8 °C is detected at all locations around 1980 from the observed and most of the simulated time series. However, no statistically significant monotonic trends emerge for both P and T. All models simulate the seasonality of T quite well. The phasing of the seasonal cycle of P is reproduced fairly well in one of the upper, snow-dominated sub-basins. Model performances degrade in the larger sub-basins that include semi-arid areas, because several GCMs are not able to capture the effect of the North American monsoon. Finally, the relative performances of the climate models in reproducing the climatologies of P and T are quantified to support future impact studies in the basin.
... As these large-scale climate phenomena are repetitive, they are categorized as patterns (Pozo et al., 2005), which can be effective both locally and globally and create much variability in climate parameters. Furthermore, they can result in drought and wet periods worldwide by changing precipitation trends (Hidalgo and Dracup, 2003;Zahraei and Karamouz, 2004;Kampichler et al., 2012;Choubin et al., 2014;Ouyang et al., 2014;Degefu and Bewket, 2017;Xu et al., 2018). Many definitions have been suggested for these patterns, which the main one identifies the teleconnection as a large-scale atmospheric-oceanic pattern, which is constant, repetitive and large-scale oscillated in some parameters, such as pressure (Wallace and Gutzler, 1981). ...
Article
Full-text available
global warming is one of the most complicated challenges of our time causing considerable tension on our societies and on the environment. The impacts of global warming are felt unprecedentedly in a wide variety of ways from shifting weather patterns that threatens food production, to rising sea levels that deteriorates the risk of catastrophic flooding. Among all aspects related to global warming, there is a growing concern on water resource management. This field is targeted at preventing future water crisis threatening human beings. The very first stage in such management is to recognize the prospective climate parameters influencing the future water resource conditions. Numerous prediction models, methods and tools, in this case, have been developed and applied so far. In line with trend, the current study intends to compare three optimization algorithms on the platform of a multilayer perceptron (MLP) network to explore any meaningful connection between large-scale climate indices (LSCIs) and precipitation in the capital of Iran, a country which is located in an arid and semi-arid region and suffers from severe water scarcity caused by mismanagement over years and intensified by global warming. This situation has propelled a great deal of population to immigrate towards more developed cities within the country especially towards Tehran. Therefore, the current and future environmental conditions of this city especially its water supply conditions are of great importance. To tackle this complication an outlook for the future precipitation should be provided and appropriate forecasting trajectories compatible with this region’s characteristics should be developed. To this end, the present study investigates three training methods namely backpropagation (BP), genetic algorithms (GAs), and particle swarm optimization (PSO) algorithms on a MLP platform. Two frameworks distinguished by their input compositions are denoted in this study: Concurrent Model Framework (CMF) and Integrated Model Framework (IMF). Through these two frameworks, 13 cases are generated: 12 cases within CMF, each of which contains all selected LSCIs in the same lead-times, and one case within IMF that is constituted from the combination of the most correlated LSCIs with Tehran precipitation in each lead-time. Following the evaluation of all model performances through related statistical tests, Taylor diagram is implemented to make comparison among the final selected models in all three optimization algorithms, the best of which is found to be MLP-PSO in IMF.
... The IDAG (International Ad Hoc Detection and Attribution Group, Zwiers, F, et al, 2005) summarized that the combination of La Niña and reduced moisture supply from the Gulf of Mexico likely led to the severe North American drought. Ropelewski & Halpert [1986] and Hidalgo & Dracup [2003] concluded that in general, southwestern U.S. cold season precipitation tends to be wetter than normal during El Niño events (negative phase of the Southern Oscillation), while drier than normal during La Niña events (positive phase of the Southern Oscillation). But the opposite effect is observed for the northwestern USA, creating a bipolar response between the two regimes. ...
... The objectives of this study are to: (Iorns et al. 1965, Van Steeter and Pitlick 1998, Hidalgo and Dracup 2003. ...
... Channel morphologies vary from restricted, high gradient, canyon reaches to wide, braided, alluvial valley reaches(Muth et al. 2000). The region has a semi-arid, high desert climate, where streamflow is largely dependent on winter precipitation stored as snowpack and is regulated by multiple diversion structures and storage reservoirs(Iorns et al. 1965;Van Steeter and Pitlick 1998;Hidalgo and Dracup 2003). Snowmelt runoff produces highest flows in spring to early summer, which decline to base levels in midsummer. ...
Article
Worldwide and likewise in Ecuador the 1982–1983 and 1997–1998 El Niño Southern Oscillation (ENSO) events had devastating effects in the economic and human dimension. Thus, scientists and decision markers look for a deeper knowledge about ENSO and its phases El Niño (EN)/La Niña (LN). Recent research highlights the changing nature of ENSO under opposite conditions of the Pacific Decadal Oscillation (PDO), making the assessment of the ENSO‐PDO relation in Ecuador urgent. This study explores the time‐frequency characteristics of rainfall in the coast of Ecuador from January to April (PC‐JA) and evaluates the influence of PDO in the relation of ENSO with PC‐JA. For this, wavelet analysis was used to asses this non‐stationary problem, Five long‐term (1964–2014) ground stations were used. The main results indicate that during the warm PDO period 1980–2000, the high wavelet coherence (ca. 0.9) implies a strong coupling between ENSO and PC‐JA. For cold PDO periods, prior to 1980 and after 2005, such coupling weakens with coherence ca. 0.5. This might indicate that PDO influence the relation between ENSO and rainfall in the coast of Ecuador. This coupling, during warm PDO, enhances high rainfall when in phase with EN, and drought conditions in LN events. The weak coupling of ENSO‐PC‐JA during cold PDO produces high rainfall amounts in Niño Neutral conditions and droughts during Neutral and LN. To account for ENSO flavors variability, the wavelet coherence between PC‐JA and the two ENSO uncorrelated indices E and C from Takahashi et al., 2011 was studied. Interestingly, we show that PDO warm phase influences the relation of Eastern Pacific related E index with PC‐JA from 2 to 8 years periods, and that the orthogonal Central Pacific related C index is not affected. These results raise questions about the validity of ENSO indices for contrasting PDO phases. This article is protected by copyright. All rights reserved.
Article
Three generations of global climate models (GCMs), Coupled Model Intercomparison Project version 3 (CMIP3), CMIP5, and CMIP6, are evaluated for performance simulating seasonal mean and annual‐to‐decadal variability of temperature and precipitation in the Upper Colorado River Basin. Low‐frequency precipitation variability associated with drought is a particular focus and found to be a significant model shortcoming. The evaluation includes remote teleconnected atmospheric responses to the Pacific Ocean, including the El Niño/Southern Oscillation and Pacific Decadal Oscillation. GCMs have improved their simulation of the Upper Basin over model generations, but primarily in atmospheric circulation metrics. Persistent winter precipitation biases have changed little, including in multiyear precipitation variability. Users generally bias‐corrected GCM data before use; evaluation using a simple spatially and temporally averaged bias correction shows that the CMIP6 models outperform earlier generations after the bias correction, although more complex precipitation biases remain even after the simple bias correction. These model rankings will be useful when selecting GCMs for a variety of hydrological and ecological climate studies in the Upper Basin.
Article
The seasonal mean atmospheric precipitable water and water vapor transport over the Haihe River Basin (HRB) in North China with a focus on their interannual to interdecadal variability, and then the relationships of the interannual and interdecadal variability of the water cycle over the HRB to the Pacific Decadal Oscillation (PDO) and El Nino-Southern Oscillation (ENSO) phenomena were investigated using the observational and National Centers for Environmental Prediction (NCEP) reanalysis data. There was a strong interdecadal variability for the water cycle (such as precipitation and water vapor transport) over the region, with an abrupt change occurring mostly in the mid 1970s. The intensity of the East Asian summer monsoon largely affected the atmospheric water vapor transport. Generally, the net meridional convergence of the water vapor flux over the region was relatively large before 1965, and it declined gradually from then on with a further notable decrease since mid 1970s. Zonal water vapor transport was similar to meridional, but with a much smaller magnitude and no noteworthy turning in the mid 1970s. Results also suggested that the wind field played an important role in the water vapor transport over the HRB before the mid 1960s, and the interdecadal variability of the water cycle (precipitation, water vapor transport, etc.) in the summer was related to the PDO; however, interannual variation of the water vapor transport could also be related to the ENSO phenomena.
Article
The method of Outcalt et al., based on work developed originally by Hurst, is re‐examined to evaluate its efficacy in delineating changes in trends and identifying regime shifts in climatic‐related time series. This technique is based on the concept of the normalized rescaled running sum where temporal changes in the Hurst exponent can be used to identify climatic trends from one regime to another as each regime has a characteristic distribution that differs from the statistical characteristics of the complete time series. An examination of the temporal change in the amplitude of the normalized rescaled running sum can be used as a method to identify these regime changes, which may be either real (i.e., a true climatic shift) or induced (i.e., through a change in measurement bias, station location, or other nonclimatic influence). Examples shown here focus on examining time series of the Pacific Decadal Oscillation, Arctic thaw depth, the Northern Hemisphere snow cover extent, treeflow data from Lees Ferry (AZ), North Atlantic tropical cyclone frequency, and central England air temperatures. The method of Outcalt et al. is re‐examined to evaluate its efficacy in delineating changes in trends and identifying regime shifts in climatic‐related time series. It is based on the normalized rescaled running sum where temporal changes in the Hurst exponent identify climatic trends from one regime to another. Examples focus on the Pacific Decadal Oscillation, Arctic thaw depth, the Northern Hemisphere snow cover extent, treeflow data from Lee’s Ferry, North Atlantic tropical storm frequency, and central England air temperatures.
Article
This exploratory study defines and characterizes large precipitation events (LPEs) at a sample of snow telemetry (SNOTEL) sites located in headwater subbasins of the Upper Colorado River Basin (UCRB) and assesses the relationships of interannual LPE variability on basin streamflow. LPE thresholds are defined as the 80th percentile of daily precipitation increments observed at each SNOTEL site from 1981 to 2014. On average, LPEs accounted for more than half (55.5%) of annual precipitation. Total precipitation, total LPE precipitation, LPE count, and LPE magnitude are assessed annually at each SNOTEL site. Statistical analysis shows that these LPE metrics, observed at the headwater SNOTEL sites, are strongly correlated with total annual streamflow downstream, as measured at river gages on major tributaries in the UCRB and at Lake Powell. Further analysis of streamflow during the early twenty-first century drought suggests that drought conditions have coincided with lower precipitation observed at the SNOTEL sites, due in part to fewer and drier LPEs in recent years. Investigation of upper air patterns during LPEs reveals that such events most commonly coincide with zonal, onshore flow among the northern subbasins and amplified troughs towards the south of the UCRB, patterns which have been less common during the drought.
Article
Regions of strong land-atmosphere coupling are often depicted as static in time. However, the mechanisms through which the land surface impacts atmospheric conditions vary on sub-daily to multi-decadal timescales. Therefore, characterizing the long-term variability of land-atmosphere interactions may provide a means of predicting when surface-induced extreme temperature events will be more or less likely to occur. We evaluate the coupling strength between soil moisture, as represented by in situ observations and 1-month Standardized Precipitation Index (SPI), and subsequent monthly maximum temperature (TMAX) over the contiguous United States. We find that the utility of SPI as a proxy for soil moisture anomalies is limited to the summer, as the correlations between SPI and TMAX are not significantly related in the other seasons. We examine the variability in summer SPI-TMAX coupling in four regions of the United States. In general, we find the strongest relationships between SPI and TMAX in the Southern Great Plains. However, our results demonstrate that the coupling strength varies considerably over time in most regions of the United States. The long-term variability in SPI-TMAX coupling strength is strongly related to the Pacific Decadal Oscillation in the northwest and midwest United States, and the Atlantic Multidecadal Oscillation in the southeast United States The results of this study suggest that land-atmosphere coupling in the contiguous United States is modulated by multi-decadal oscillations in Pacific and Atlantic sea surface temperatures.
Article
Full-text available
Low flow magnitude in a head water basin is important for planners because minimum available amount of water in a given time period often leads to concerns regarding serious repercussions, in both up and downstream regions. This is a common scenario in arid region like Colorado River basin located in the southwestern US. Low flow variability in Colorado River is due to complex interactions between several natural and anthropogenic factors; but we aim to identify the relative role of climate on varying low flow magnitudes at different spatial locations. The research questions we aim to answer are: Is there a systematic variability in water availability during the driest time of a year or season? How does that vary across locations and is there a link between large-scale climate and low flow variations? Towards that aim we select 17 stream gauge locations, which are identified as "undisturbed" meaning that these stations represent near-natural river flow regimes in the headwater region of Colorado River, which provides a useful resource for assessment of climate and hydrology associations without the confounding factor of major direct (e.g. water abstraction) or indirect (e.g. land-use change) human modification of flows. A detailed diagnostic analysis gives us fair understanding on the variability of low flow magnitude that is explained by climate. We also present spatial heterogeneity of hydro-climatological linkages that is important for suitable adaptive management measures.
Article
We use new and established methodologies in multivariate time series analysis to study the dynamics of 414 Australian hydrological stations’ streamflow. First, we analyze our collection of time series in the temporal domain, and compare the similarity in hydrological stations’ candidate trajectories. Then, we introduce a Whittle Likelihood-based optimization framework to study the collective similarity in periodic phenomena among our collection of stations. Having identified noteworthy similarity in the temporal and spectral domains, we introduce an algorithmic procedure to estimate a governing hydrological streamflow process across Australia. To determine the stability of such behaviours over time, we conclude by studying the evolution of the governing dynamics and underlying time series with time-varying applications of principal components analysis (PCA) and eigenspectrum analysis.
Article
While many studies have described linkages between large-scale climate phenomena and precipitation and streamflow, fewer studies explicitly address the climatic modulations at sub-regional scales. This study quantifies statistically the temporal variability in precipitation and streamflow at a regional scale in the semi-arid area of South Texas associated with three climate indices: El Niño-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and Atlantic Multidecadal Oscillation (AMO). Results show that ENSO and PDO strongly modulate rainfall during the cold season and, to various extents, streamflow during the cold and warm seasons. In addition, this study shows that in South Texas streamflow is consistently below normal (i.e. means) while precipitation slightly increases during AMO-warm. To different extents, the Pacific and Atlantic Sea Surface Temperature (SST) anomalies show stronger influences on the climate of South Texas when coupled. Droughts are more correlated with La Niña events but these events play a secondary role during PDO-cold. Although the PDO-cold phase is the dominant driver of droughts in this area, our analyses also show that the coupled effect of the PDO-cold/AMO-warm phases significantly increases the intensity of drought conditions to a degree similar to the PDO-cold/La Niña coupled effect. Given its stronger response to climate anomalies, streamflow offers a more effective tool for predicting climate variability impacts on South Texas water resources when compared to precipitation.
Article
Full-text available
Periodic fluctuations in natural streamflow are a major driver of river ecosystem dynamics and water resource management. However, most U.S. rivers are impacted both by long‐term hydroclimatic trends and dams that alter flow variability. Despite these impacts, it remains largely unexplored how dams affect the dominant frequencies of natural streamflow over a highly regulated river network. We investigated the entire Colorado River Basin (CRB) to understand how the annual (10–14 months) and multi‐annual (24–60 months) frequencies in natural flow regimes have been progressively altered by dams. Given the significant alteration over the CRB, we captured changes in streamflow frequencies between naturalized and observed monthly flows via wavelet analysis. Based on the similarity of changes in streamflow frequencies (annual and multi‐annual) over the last 30 years, sections of the riverine network were classified into four groups. The annual frequency was relatively well preserved downstream of Hoover Dam, while showing a systematic trend of alteration downstream of Glen Canyon Dam until Hoover Dam. Meanwhile, the multi‐annual frequency component was highly altered for the entire Lower Colorado main stem (i.e., downstream of Glen Canyon). We also identified dams with significant impacts on streamflow frequency by comparing wavelet coherence estimates. This study advances the notion that dams fundamentally alter river flow regimes across multiple frequencies and with varying amplitudes over time and space, with alteration propagating – or being dampened – by both hydroclimatic fluctuations and water resource management.
Article
Full-text available
Annual net balance eight North Cascade glaciers during the 1984-94 period has been determined by measurement of total mass loss firn and ice melt and ice melt and, residual snow depth at the end of the Summer season. Overall spatial density of measurment points is 200 points km−2. Mean annual balance of North Clascade glaciers from 1984 to 1994 has been −0.38 ma−1. The resulting 4.2 m loss in water-equivalent thickness is significant, since North Cascade glaciers have an average thickness of 30–50 m. Cross-correlation of annual net balance Ior eight glaciers ranges from 0.83 to 0.97. This indicates the mass balances of the eight glaciers have been responding similarly to elimate conditions despite their range of topographic and geographic characteristics. Annual net balance of individual glaciers was correlated with climate records. The highest ablation-season correlation coefficient is mean May–August temperature, ranging from 0.63 to 0.84. The highest accumulation-season correlation coefficient is total accumulation-season precipitation, ranging from 0.35 to 0.59.
Article
Full-text available
We present here a six-species comparison of tree-ring growth response to extremes (below the 30th and above the 70th percentile) in temperature, precipitation, and corresponding streamflow. The species compared are Pinus edulis (PIED), Pseudotsuga menziesii (PSME), Pinus ponderosa (PIPO), Pinus flexilis (PIFL), Pinus aristata (PIAR), and Picea engelmannii (PCEN). Sensitivity was determined using contingency scores obtained by comparing tree-ring growth at different lags with hydroclimatic observations from the Upper Colorado River Basin in the southwestern United States. The scores were computed using dual scaling methods in which the higher scores are assigned to stronger relationships between tree-ring growth and severe hydroclimatic occurrences. At lag 0, PIED and PSME present the greatest sensitivity to severe streamflow events. For precipitation and temperature the most sensitive species at lag 0 are PIED and PIPO. PIAR and PCEN show no significant relationship with extreme hydroclimatic events. PIFL shows more uniform lag-to-lag scores, suggesting a higher year-to-year persistence for this species. In general, tree-ring growth for all sensitive species is more responsive to hot-dry than to cool-moist extreme conditions. The scoring method proposed in this study for the analysis of tree-ring records proved to be a useful tool for evaluating ring-width sensitivity to extreme climatic forcing.
Article
Full-text available
Annual net balance eight North Cascade glaciers during the 1984-94 period has been determined by measurement of total mass loss firn and ice melt and ice melt and, residual snow depth at the end of the Summer season. Overall spatial density of measurment points is 200 points km ⁻² . Mean annual balance of North Clascade glaciers from 1984 to 1994 has been −0.38 ma ⁻¹ . The resulting 4.2 m loss in water-equivalent thickness is significant, since North Cascade glaciers have an average thickness of 30–50 m. Cross-correlation of annual net balance Ior eight glaciers ranges from 0.83 to 0.97. This indicates the mass balances of the eight glaciers have been responding similarly to elimate conditions despite their range of topographic and geographic characteristics. Annual net balance of individual glaciers was correlated with climate records. The highest ablation-season correlation coefficient is mean May–August temperature, ranging from 0.63 to 0.84. The highest accumulation-season correlation coefficient is total accumulation-season precipitation, ranging from 0.35 to 0.59.
Article
Full-text available
Changes in the peak wind gust magnitude in association with the warm and cold phases of the El Niño-Southern Oscillation (ENSO) are identified over the contiguous United States. All calculations of the peak wind gust are differences in the extreme phases of ENSO (warm and cold) relative to neutral for all stations in the study that pass the completeness criteria. Monthly composites were created for all years in the study (1 January 1948 through 31 August 1998). The differences in the mean peak wind gust are calculated for each month. A nonparametric statistical test was invoked to determine significant shifts in the extreme phase distributions. Differences in the frequency of gale-force wind gusts were also calculated. The results show a dominant, ENSO cold phase wintertime signal. Regions most greatly affected are the Pacific Northwest. Southwest, the Great Plains, and the region extending from the Great Lakes through the Ohio River valley, and southwest into Texas. During the cold phase months from November to March, these regions experience an overall increase in the gustiness of the winds. The warm phase is associated with overall decreased gustiness in the Pacific Northwest during these months: however, the signal is of a lesser magnitude. There is also an observed decrease in the central Great Plains during the warm phase months of April and June. These results, along with improved ENSO forecasting, can work toward mitigating adverse effects of strong wind gusts and increase the utilization of wind power.
Article
Full-text available
The relationship between the three primary modes of Pacific sea surface temperature (SST) variability-the El Niño-Southern Oscillation (ENSO), the Pacific decadal oscillation, and the North Pacific mode-and U.S. warm season hydroclimate is examined. In addition to precipitation, drought and stream flow data are analyzed to provide a comprehensive picture of the lower-frequency components of hydrologic variability.ENSO and the two decadal modes are extracted from a single unfiltered analysis, allowing a direct intercomparison of the modal structures and continental linkages. Both decadal modes have signals in the North Pacific, but the North Pacific mode captures most of the local variability. A summertime U.S. hydroclimatic signal is associated with all three SST modes, with the linkages of the two decadal modes comparable in strength to that of ENSO.The three SST variability modes also appear to play a significant role in long-term U.S. drought events. In particular, the northeastern drought of the 1960s is shown to be closely linked to the North Pacific mode. Concurrent with the drought were large positive SST anomalies in the North Pacific, quite similar in structure to the North Pacific mode, and an example of a physical realization of the mode. Correspondingly, the 1962-66 drought pattern had considerable similarity to the drought regression associated with the North Pacific mode. Analysis of upper-level stationary wave activity during the drought period shows a flux emanating from the North Pacific and propagating over the United States. The near-equivalent-barotropic circulation anomalies originating in the North Pacific culminate in a cyclonic circulation over the East Coast that, at low levels, opposes the climatological inflow of moisture in an arc over the continent from the Gulf Coast to the Northeast, consistent with the observed drought.
Article
Full-text available
We present global fields of decadal annual surface temperature anomalies, referred to the period 1951-1980, for each decade from 1881-1890 to 1981-1990 and for 1984-1993. In addition, we show decadal calendar-seasonal anomaly fields for the warm decades 1936-1945 and 1981-1990. The fields are based on sea surface temperature (SST) and land surface air temperature data. The SSTs are corrected for the pre-World War II use of uninsulated sea temperature buckets and incorporate adjusted satellite-based SSTs from 1982 onward. The generally cold end of the nineteenth century and start to the twentieth century are confirmed, toegether with the substantial warming between about 1920 and 1940. Slight cooling of the northern hemisphere took place between the 1950s and the mid-1970s, although slight warming continued south of the equator. Recent warmth has been most marked over the northern continents in winter and spring, but the 1980s were warm almost everywhere. -from Authors
Article
Full-text available
A long time series of monthly soil moisture data during the period of 1931-1993 over the entire U.S. continent has been created with a one-layer soil moisture model. The model is based on the water budget in the soil and uses monthly temperature and monthly precipitation as input. The data are for 344 U.S. climate divisions during the period of 1931-1993. The main goals of this paper are 1) to improve our understanding of soil moisture and its effects on the atmosphere and 2) to apply the calculated soil moisture toward long-range temperature forecasts.In this study, the model parameters are estimated using observed precipitation, temperature, and runoff in Oklahoma (1960-1989) and applied to the entire United States. The comparison with the 8-yr (1984-1991) observed soil moisture in Illinois indicates that the model gives a reasonable simulation of soil moisture with both climatology and interannual variability.The analyses of the calculated soil moisture show that the climatological soil moisture is high in the east and low in the west (except the West Coast), which is determined by the climatological precipitation amounts. The annual cycle of soil moisture, however, is determined largely by evaporation. Anomalies in soil moisture are driven by precipitation anomalies, but their timescales are to first order determined by both climatological temperature (through evaporation) and climatological precipitation. The soil moisture anomaly persistence is higher where normal temperature and precipitation are low, which is the case in the west in summer. The spatial scale of soil moisture anomalies has been analyzed and found to be larger than that of precipitation but smaller than that of temperature.Authors found that generally in the U.S. evaporation anomalies are much smaller in magnitude than precipitation anomalies. Furthermore, observed and calculated soil moisture anomalies have a broad frequency distribution but not the strongly bimodal distribution indicative of water recycling.Compared to antecedent precipitation, soil moisture is a better predictor for future monthly temperature. Soil moisture can provide extra skill in predicting temperature in large areas of interior continent in summer, particularly at longer leads. The predictive skill of soil moisture is even higher when the predictand is daily maximum temperature instead of daily mean temperature.
Article
Full-text available
A newly available, extensive compilation of upper-ocean temperature profiles was used to study the vertical structure of thermal anomalies between the surface and 400-m depth in the North Pacific during 1970-1991. A prominent decade-long perturbation in climate occurred during this time period: surface waters cooled by 1°C in the central and western North Pacific and warmed by about the same amount along the west coast of North America from late 1976 to 1988. Comparison with data from COADS suggests that the relatively sparse sampling of the subsurface data is adequate for describing the climate anomaly.The vertical structure of seasonal thermal anomalies in the central North Pacific shows a series of cold pulses beginning in the fall of 1976 and continuing until late 1988 that appear to originate at the surface and descend with time into the main thermocline to at least 400-m depth. Individual cold events descend rapidly (100 m yr1), superimposed upon a slower cooling (15 m yr1). The interdecadal climate change, while evident at the surface, is most prominent below 150 m where interannual variations are small. Unlike the central North Pacific, the temperature changes along the west coast of North America appear to be confined to approximately the upper 200-250 m. The structure of the interdecadal thermal variations in the eastern and central North Pacific appears to be consistent with the dynamics of the ventilated thermocline. In the western North Pacific, strong cooling is observed along the axis of the Kuroshio Current Extension below 200 m depth during the 1980s.Changes in mixed layer depth accompany the SST variations, but their spatial distribution is not identical to the pattern of SST change. In particular, the decade-long cool period in the central North Pacific was accompanied by a 20 m deepening of the mixed layer in winter, but no significant changes in mixed layer depth were found along the west coast of North America. It is suggested that other factors such as stratification beneath the mixed layer and synoptic wind forcing may play a role in determining the distribution of mixed layer depth anomalies.
Article
Full-text available
A new NOAA definition of El Niño identifies a number of additional El Niño seasons beyond those conventionally agreed. These additional seasons are characterized by SST anomalies primarily in the western central equatorial Pacific. We show here that the seasonal weather anomalies over the U.S. associated with these additional Dateline El Niño seasons are substantially different from those associated with conventional El Niño seasons. Although some regions have similar associated anomalies, most of the major regional anomalies are quite different. Treating the two as a single phenomenon yields weaker overall seasonal weather associations and does not take advantage of the stronger associations available when the two are treated separately.
Article
Full-text available
The present study documents seasonal rainfall anomalies in East Asia during different phases of El Niño Southern Oscillation (ENSO) using station rainfall and the NCEP NCAR reanalysis for the period of 1951 2000 through lag lead correlation/regression and extended singular value decomposition analyses. The ENSO-related rainfall anomalies consist of two major evolving centers of action: one positive and the other negative. The positive center of action affects southern China, eastern central China, and southern Japan during the fall of an ENSO developing year through the following spring. The negative center of action is over northern China during the summer and fall of an ENSO developing year. Seasonal rainfall variance explained by ENSO is about 20% 30% in southern China in fall and winter, about 20% in eastern central China in spring after the mature phase of ENSO, and around 15% 20% in western north China in summer and fall of an ENSO developing year.The two main rainfall anomalies are induced by different anomalous circulation systems. The positive center of action is closely related to an anomalous low-level anticyclone over the western North Pacific. The anomalous anticyclone develops over the South China Sea in fall and extends eastward in winter and moves northeastward in spring and summer. The evolution of this anticyclone is determined by large-scale equatorial heating anomalies and local air sea interactions. The negative center of action in northern China is associated with an anomalous barotropic cyclone displacing southwestward along the East Asian coast during the developing stage of ENSO. Evolution of this cyclone is affected by anomalous heating over south Asia and the western North Pacific.
Article
Full-text available
Three-day accumulations of precipitation for 2.5° long × 2.0° lat areas along the west coast of the United States are used to rank precipitation events. Extreme precipitation events (those above the 90th percentile) occur at all phases of the El Niño-Southern Oscillation (ENSO) cycle, but the largest fraction of these events (for the West Coast as a whole) occur during neutral winters just prior to the onset of El Niño. In the tropical Pacific these winters are characterized by enhanced activity on intraseasonal (roughly 20-60 day) timescales and by relatively small sea surface temperature anomalies compared to ENSO winters. For these winters, lagged composites are used to document a coherent relationship between the location of extreme precipitation events along the West Coast and the location of enhanced tropical convection on intraseasonal timescales. The evolution of the atmospheric circulation patterns associated with the extreme precipitation events is described and a physical mechanism relating tropical intraseasonal oscillations, the `pineapple express,' and the extreme precipitation events is proposed and illustrated.
Article
Full-text available
Summer rainfall in the central United States has singular interannual variations of a 3-6-yr period. Identifying the causes of these variations assures improvement in predictions of summer rainfall in the region.A review of previous studies revealed a puzzling situation: the outstanding interannual variations of the summer rainfall in the central United States showed no persistent correlations with known influential interannual variations in the Northern Hemisphere and the El Niño-Southern Oscillation (ENSO). This study was undertaken to identify the cause of this situation and ultimately explain the causes of the observed interannual summer rainfall variations. Its results showed a teleconnection of the ENSO with the summer rainfall in the central United States. The intensity of which has varied over the last 125 years. The teleconnection was active in two epochs, 1871-1916 and 1948-78, and absent in the two epochs 1917-47 and 1979-present. This variation was associated with a multidecadal variation in both sea surface temperature and sea level pressure in the mid- and high-latitude North Pacific. In the epochs of active teleconnection, the circulation in the warm phase of ENSO favored a deformation field in the lower troposphere in the central United States causing wet summers and a reversed circulation in cold phase of ENSO yielding dry summers, a process that partially explains the interannual summer rainfall variations.The result also showed that the variations of the teleconnection were `in phase' with the variation in the average surface temperature of the Northern Hemisphere. When the `abrupt warming' of the surface temperature developed in 1917-47 and the most recent two decades, the teleconnection broke down. Because of the limitation in data record length, this observed relationship and the persistence of the variation in the teleconnection need further investigations when additional data are available.
Article
Full-text available
Observational analyses are performed to examine the roles of remote and local forcing in the evolutions of the extreme US summer heat wave-drought cases of 1980 and 1988. At early stages, both events are associated with anomalous stationary wave patterns. Wave activity flux analyses suggest that in the 1980 case anomalous wave activity propagates southeastward from an apparent source region to the south of the Aleutians. The flux pattern is more complex in the 1988 case but suggests two possible source regions, one over the central North Pacific to the north of the Hawaiian Islands and a second located over the far western Pacific. Overall, the results indicate the importance of both dynamical forcing from remote sources and anomalous local boundary conditions in accounting for the two extreme heat wave-drought events. -from Authors
Article
Full-text available
Indices of the dominant spatial patterns of wintertime Northern Hemisphere 500-mb height and North Pacific sea surface temperature are strongly correlated with one another on interannual and interdecadal timescales, and both am correlated with indices of the El Niñ-Southern Oscillation. One possible interpretation of these relationships is that the tropical SST anomalies associated with ENSO force the atmospheric circulation over the North Pacific, and these atmospheric anomalies, in turn, give rise to the observed SST anomalies over the extratropical North Pacific.In this study, linear relationships between ENSO and extratropical variables are examined in two different ways. First, the component of the observed extratropical variability that is linearly dependent upon ENSO is removed. The dominant spatial patterns in the residual variability of 500-mb height and SST anomalies over the North Pacific are shown to be similar to their counterparts in the total fields and remain strongly coupled on both interannual and interdecadal timescales. Second, the 44 winters used in the analysis are divided into strong ENSO and weak ENSO groups in accordance with the absolute magnitude of ENSO SST anomalies during that winter. Consistent with the analysis of the residual fields, the dominant patterns in extratropical 500-mb height and SST over the North Pacific are strongly coupled, even during winters in which tropical Pacific SST anomalies are weak. An alternative analysis, in which a 15-year record of MSU tropical precipitation data is used as a basis for defining the ENSO signal, yields similar results. The linear relation between SST in the western tropical Pacific and extratropical circulation anomalies is also examined and found to be weak.
Article
Full-text available
Streamflows in the Pacific Southwest of the United States in relation to the tropical Type 1 El Niño-Southern Oscillation (T1ENSO) and La Niña events are examined using composite and harmonic analyses for each event during a 24-month evolution period. The hydroclimatic signals associated with either extreme phase of the Southern Oscillation (SO) are explored based on data from 50 streamflow stations in California, Arizona, New Mexico, Colorado, and Utah. A significant level for the results is assessed by the use of a hypergeometric distribution. Highly significant, coherent signals are demonstrated to exist for both events, with opposite sign and almost identical timing. Pacific Southwest streamflow responses to the T1ENSO thermal forcing are characterized by a wet December-July season in the subsequent year of the event. Similarly, a dry February-July season is detected as a period at which the La Niña-streamflow relationship is strong and spatially coherent. An index time series is plotted to determine the temporal consistency of the signal. It was found that the respective seasonal signal for each event was confirmed by all episodes. Amplification (suppression) of the regional annual streamflow cycle is noticed during the subsequent year of the typical T1ENSO (La Niña) event.A lag cross-correlation analysis is conducted between the time series of the seasonal December-July streamflow index and the SO index. The March-May season in the previous year of the seasonal T1ENSO signal was determined to be the logical period in which the SO index can be averaged to obtain the highest correlation and the maximum time lag. A Mann-Whitney U test reveals statistically significant differences in the means of seasonal streamflows associated with T1ENSO and La Niña events. Plausible explanations for the observed teleconnections are presented.
Article
Full-text available
The relationship between the relative variability of annual rainfall, the long-term mean annual rainfall, the latitude, and the correlation between annual rainfall and the Southern Oscillation Index is examined, using data from 974 stations. A nonlinear relationship between these variables accounts for 94% of the variance in annual rainfall variability. Relative variability typically increases as mean annual rainfall decreases, as latitude decreases, and as the effect of the Southern Oscillation increases. There is an interaction between latitude and the Southern Oscillation so that the effect of the Southern Oscillation on variability weakens as latitude increases.
Article
Satellite passive microwave observations can provide unique mesoscale (25 km) information on snowpack properties; however, the mountainous terrain of the upper Colorado River basin compounds the difficulty of the problem. Nevertheless, observations of this region from the Scanning Multichannel Microwave Radiometer (SMMR) have provided unique, synoptic, mesoscale snowpack information from 1979 to 1987 on the snowpack extent. For this nine-year period, the SMMR 18 and 37 GHz brightness temperature observations, combined to form a parameter called NGR, show the average maximum snowpack extent covers 70% of the basin and occurs on water year day 130 (mid-February). The minimum snowpack extent took place in 1981 and covered 35% of the basin. The maximum snowpack extent took place in 1979 and covered 99% of the basin. Summation of the NGR values from each SMMR mesoscale pixel within the basin provides an index of the regional snowpack properties on both an intra- and inter-annual basis and exhibits behavior similar to the snowpack extent. When compared to the nine-year average, 1981 is the minimum year and 1979 is the maximum year. Furthermore, the sum over the basin of the annual maximum NGR from each pixel correlates with the annual discharge, r = 0.6. This correlation increases to 0.8 when digital elevation data are used to characterize each SMMR pixel and only the April through July discharge is used in the regression. Hence, this study combines the small scale elevation data with the mesoscale SMMR observations to investigate the basin-wide or regional snowpack characteristics and its hydrology.
Article
Frequency distributions of daily precipitation in winter and daily stream flow from late winter to early summer, at several hundred sites in the western United States, exhibit strong and systematic responses to the two phases of ENSO. Most of the stream flows considered are driven by snowmelt. The Southern Oscillation index (SOI) is used as the ENSO phase indicator. Both modest (median) and larger (90th percentile) events were considered. In years with negative SOI values (El Nino), days with high daily precipitation and stream flow are more frequent than average over the Southwest and less frequent over the Northwest. During years with positive SOI values (La Nina), a nearly opposite pattern is seen. A more pronounced increase is seen in the number of days exceeding climatological 90th percentile values than in the number exceeding climatological 50th percentile values, for both precipitation and stream flow. Stream flow responses to ENSO extremes are accentuated over precipitation responses. Evidence suggests that the mechanism for this amplification involves ENSO-phase differences in the persistence and duration of wet episodes, affecting the efficiency of the process by which precipitation is converted to runoff. The SOI leads the precipitation events by several months, and hydrologic lags (mostly through snowmelt) dealy the stream flow response by several more months. The combined 6-12 month predictive aspect of this relationship should be of significant benefit in responding to flood (or drought) risk and in improving overall water management in the western states.
Article
The overall amount of precipitation deposited along the West Coast and western cordillera of North America from 25°to 55°N varies from year to year, and superimposed on this domain-average variability are varying north-south contrasts on timescales from at least interannual to interdecadal. In order to better understand the north-south precipitation contrasts, their interannual and decadal variations are studied in terms of how much they affect overall precipitation amounts and how they are related to large-scale climatic patterns. Spatial empirical orthogonal functions (EOFs) and spatial moments (domain average, central latitude, and latitudinal spread) of zonally averaged precipitation anomalies along the westernmost parts of North America are analyzed, and each is correlated with global sea level pressure (SLP) and sea surface temperature series, on interannual (defined here as 3-7 yr) and decadal (>7 yr) timescales. The interannual band considered here corresponds to timescales that are particularly strong in tropical climate variations and thus is expected to contain much precipitation variability that is related to El Nino-Southern Oscillation; the decadal scale is defined so as to capture the whole range of long-term climatic variations affecting western North America. Zonal EOFs of the interannual and decadal filtered versions of the zonal-precipitation series are remarkably similar. At both timescales, two leading EOFs describe 1) a north-south seesaw of precipitation pivoting near 40°N and 2) variations in precipitation near 40°N, respectively. The amount of overall precipitation variability is only about 10% of the mean and is largely determined by precipitation variations around 40°-45°N and most consistently influenced by nearby circulation patterns; in this sense, domain-average precipitation is closely related to the second EOF. The central latitude and latitudinal spread of precipitation distributions are strongly influenced by precipitation variations in the southern parts of western North America and are closely related to the first EOF. Central latitude of precipitation moves south (north) with tropical warming (cooling) in association with midlatitude western Pacific SLP variations, on both interannual and decadal timescales. Regional patterns and zonal averages of precipitation-sensitive tree-ring series are used to corroborate these patterns and to extend them into the past and appear to share much long- and short-term information with the instrumentally based zonal precipitation EOFs and moments.
Article
A practical step-by-step guide to wavelet analysis is given, with examples taken from time series of the El NiñoSouthem Oscillation (ENSO). The guide includes a comparison to the windowed Fourier transform, the choice of an appropriate wavelet basis function, edge effects due to finite-length time series, and the relationship between wavelet scale and Fourier frequency. New statistical significance tests for wavelet power spectra are developed by deriving theoretical wavelet spectra for white and red noise processes and using these to establish significance levels and confidence intervals. It is shown that smoothing in time or scale can be used to increase the confidence of the wavelet spectrum. Empirical formulas are given for the effect of smoothing on significance levels and confidence intervals. Extensions to wavelet analysis such as filtering, the power Hovmöller, cross-wavelet spectra, and coherence are described. The statistical significance tests are used to give a quantitative measure of changes in ENSO variance on interdecadal timescales. Using new datasets that extend back to 1871, the Niño3 sea surface temperature and the Southern Oscillation index show significantly higher power during 1880-1920 and 1960-90, and lower power during 1920-60, as well as a possible 15-yr modulation of variance. The power Hovmöller of sea level pressure shows significant variations in 2-8-yr wavelet power in both longitude and time.
Article
On the U.S. west coast, the main toxin-producing algal species are dinoflagellates in the genus Alexandrium that cause paralytic shellfish poisoning (PSP) and diatoms in the genus Pseudo-nitzschia that produce domoic acid and cause domoic acid poisoning (DAP). Other harmful species, including the raphidophyte Heterosigma akashiwo and the diatoms Chaetoceros convulutus and Chaetoceros concavicornis, kill fish at aquaculture sites, but are not harmful to humans. Water discolorations (red tides) caused by nontoxic dinoflagellates also occur throughout the area. Early records, partially based on local native lore, suggest that algal toxins have been present along this coast for hundreds of years, but actual scientific information is sparse. We review what is now known about harmful algal blooms in this vast area, including the hydrographic regimes that induce and(or) support blooms, bloom dynamics, and the biology of the causative species.
Article
Using principal component analysis (PCA), cluster analysis, and jackknife analysis, we investigated the spatial and temporal modes that dominate streamflow variability in the western US in response to El Niño-Southern Oscillation (ENSO) events. Spatial variability was investigated with data only from ENSO years and with rotated PCA on 79 streamflow stations in the western United States. Eight regions, or clusters, were thus pinpointed as areas where streamflow tends to co-vary similarly following ENSO events; traditional cluster analysis confirmed the identification of these regions. The ENSO response in streamflow was then further evaluated by forming an aggregate ENSO composite for each region.Temporal variability of western US streamflow in the PCA-identified regions was evaluated with a ‘T-mode’ PCA that isolated the different responses in streamflow following ENSO events. The T-mode PCA breaks the 13 ENSO events that occurred from 1932 to 1993 into five subsets. It is interesting to note that the events in the dominant mode, PC1(+), occurred before 1976, and next mode, PC2(+), included events prior to 1976.Finally, we investigated the atmospheric circulation patterns over the North Pacific Ocean and much of North America that are associated with the various US streamflow responses. The circulation patterns vary according to the prescribed ENSO forcing. The results of this study contribute to a better understanding of the varied ENSO-streamflow relationship in the western US and the use of ENSO for long-range streamflow forecasting.
Article
Changing patterns of correlations between the historical average June-November Southern Oscillation Index (SOI) and October-March precipitation totals for 84 climate divisions in the western US indicate a large amount of variability in SOI/precipitation relations on decadal time scales. Correlations of western US precipitation with SOI and other indices of tropical El Niño-Southern Oscillation (ENSO) processes were much weaker from 1920 to 1950 than during recent decades. This variability in teleconnections is associated with the character of tropical air-sea interactions as indexed by the number of out-of-phase SOI/tropical sea surface temperature (SST) episodes, and with decadal variability in the North Pacific Ocean as indexed by the Pacific Decadal Oscillation (PDO). ENSO teleconnections with precipitation in the western US are strong when SOI and NINO3 are out-of-phase and PDO is negative. ENSO teleconnections are weak when SOI and NINO3 are weakly correlated and PDO is positive. Decadal modes of tropical and North Pacific Ocean climate variability are important indicators of periods when ENSO indices, like SOI, can be used as reliable predictors of winter precipitation in the US.
Article
Seasonal climate anomalies over North America exhibit rather large variability between years characterized by the same ENSO phase. This lack of consistency reduces potential statistically based ENSO-related climate predictability. The authors show that the North Pacific oscillation (NPO) exerts a modulating effect on ENSO teleconnections. Sea level pressure (SLP) data over the North Pacific, North America, and the North Atlantic and daily rainfall records in the contiguous United States are used to demonstrate that typical ENSO signals tend to be stronger and more stable during preferred phases of the NPO. Typical El Niño patterns (e.g., low pressure over the northeastern Pacific, dry northwest, and wet southwest, etc.) are strong and consistent only during the high phase of the NPO, which is associated with an anomalously cold northwestern Pacific. The generally reversed SLP and precipitation patterns during La Niña winters are consistent only during the low NPO phase. Climatic anomalies tend to be weak and spatially incoherent during low NPO-El Niño and high NPO-La Niña winters. These results suggest that confidence in ENSO-based long-range climate forecasts for North America should reflect interdecadal climatic anomalies in the North Pacific.
Article
The dynamics and predictability of decadal climate variability over the North Pacific and North America are investigated by analyzing various observational datasets and the output of a state of the art coupled ocean-atmosphere general circulation model that was integrated for 125 years. Both the observations and model results support the picture that the decadal variability in the region of interest is based on a cycle involving unstable ocean-atmosphere interactions over the North Pacific. The period of this cycle is of the order of a few decades.The cycle involves the two major circulation regimes in the North Pacific climate system, the subtropical ocean gyre, and the Aleutian low. When, for instance, the subtropical ocean gyre is anomalously strong, more warm tropical waters are transported poleward by the Kuroshio and its extension, leading to a positive SST anomaly in the North Pacific. The atmospheric response to this SST anomaly involves a weakened Aleutian low, and the associated fluxes at the air-sea interface reinforce the initial SST anomaly, so that ocean and atmosphere act as a positive feedback system. The anomalous heat flux, reduced ocean mixing in response to a weakened storm track, and anonmalous Ekman heat transport contribute to this positive feedback.The atmospheric response, however, consists also of a wind stress curl anomaly that spins down the subtropical ocean gyre, thereby reducing the poleward heat transport and the initial SST anomaly. The ocean adjusts with some time lag to the change in the wind stress curl, and it is this transient ocean response that allows continuous oscillations. The transient response can be expressed in terms of baroclinic planetary waves, and the decadal timescale of the oscillation is therefore determined to first order by wave timescales. Advection by the mean currents, however, is not negligible.The existence of such a cycle provides the basis of long-range climate forecasting over North America at decadal timescales. At a minimum, knowledge of the present phase of the decadal mode should allow a `now-cast' of expected climate `bias' over North America, which is equivalent to a climate forecast several years ahead.