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Role of the strengthened El Niño teleconnection in the May 2015 floods over the southern Great Plains


Abstract and Figures

The climate anomalies leading to the May 2015 floods in Texas and Oklahoma were analyzed in the context of El Niño teleconnection in a warmer climate. El Niño tends to increase late-spring precipitation in the southern Great Plains and this effect has intensified since 1980. There was a detectable effect of anthropogenic global warming in the physical processes that caused the persistent precipitation in May of 2015: Warming in the tropical Pacific acted to strengthen the teleconnection towards North America, modification of zonal wave-5 circulation that deepened the anomalous trough to the west of Texas, and an enhanced Great Plains low-level southerlies increasing moisture supply from the Gulf of Mexico. Attribution analysis using the CMIP5 single-forcing experiments and the CESM Large Ensemble Project indicated a significant increase in the El Niño- induced precipitation anomalies over Texas and Oklahoma when increases in the anthropogenic greenhouse gases were taken into account.
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Role of the strengthened El Niño teleconnection in the May
2015 oods over the southern Great Plains
S.-Y. Simon Wang
, Wan-Ru Huang
, Huang-Hsiung Hsu
, and Robert R. Gillies
Utah Climate Center, Utah State University, Logan, Utah, USA,
Department of Plants, Soils, and Climate, Utah State
University, Logan, Utah, USA,
Department of Earth Sciences, National Taiwan Normal University, Taipei, Taiwan,
Center for Environmental Changes, Academia Sinica, Taipei, Taiwan
Abstract The climate anomalies leading to the May 2015 oods in Texas and Oklahoma were analyzed in
the context of El Niño teleconnection in a warmer climate. A developing El Niño tends to increase late-spring
precipitation in the southern Great Plains, and this effect has intensied since 1980. Anthropogenic global
warming contributed to the physical processes that caused the persistent precipitation in May 2015: Warming
in the tropical Pacic acted to strengthen the teleconnection toward North America, modication of zonal
wave 5 circulation that deepened the stationary trough west of Texas, and enhanced Great Plains low-level
southerlies increasing moisture supply from the Gulf of Mexico. Attribution analysis using the Coupled Model
Intercomparison Project Phase 5 single-forcing experiments and the Community Earth System Model Large
Ensemble Project indicated a signicant increase in the El Niño-induced precipitation anomalies over Texas and
Oklahoma when increases in the anthropogenic greenhouse gases were taken into account.
1. Introduction
In May 2015, an El Niño had developed (Figure 1a) an d as a consequen ceat least in partprecipitation
ano malies in Texas an d Oklahoma were off the scale reaching over 200 mm above norm al (Figure 1b); this
was accompanied by dry anomalies in Kentucky and Tenne ssee. As the Texas news media echoed enough
rain fell in May to cover the entire state 8 inches deep (CNN 1 June 2015) and in Houston alone, the oo d
damage was estimated to top $45 million (Associate Press 31 May 2015). While seasonal predictions,
issued as early as March, had indicated increased May precipitation for the southern Great Plains (http://, the extreme magnitude of the rainfall was not indicated nor
anticipateda challenge that is yet to be realized.
It is known that either the onset or a persistent El Niño can increase spring precipitation in the southern Great
Plains at the same time reducing precipitation in the southeast U.S. [e.g., Ropelewski and Halpert, 1986, 1987;
S.-K. Lee et al., 2014]. Previous studies [e.g., Meehl and Teng, 2007; Stevenson et al., 2012; Wang et al., 2014]
have found that in a warmer climate, the teleconnection that underlies the El NiñoSouthern Oscillation
(ENSO) and its associated impact on North America would change in terms of intensication and/or a posi-
tional shift of the resultant climate anomalies; this is regardless of the direction of future change in frequency
and intensity that ENSO might take. Climate modications that involve ENSO have forecast implications at
both seasonal [Mo, 2010] and decadal [Meehl et al., 2014] timescales, and it is reasonable to question to what
extent, if any, the rather extreme May 2015 precipitation event that occurred during an El Niño was induced
through a warming climate. It is therefore worthwhile to conduct a climate diagnostics and an attribution
analysis of the May 2015 high-precipitation event that occurred over Texas and Oklahoma.
2. Data
We adopted 17 models from the Coupled Model Intercomparison Proj ect Phase 5s (CMIP5) historical
single-forcing experiments that were driven by (1) natural-only forcing including solar and volcano (NAT),
(2) greenhouse gas (GHG)-only forcing, and (3) all these historical forcings (ALL) including anthropogenic
aer osols [Taylor et al., 2011]. Each experiment prod uced multip le members initialized from a long-stable
preindustrial (1850) control run up to 2005. Table S1 in the supporting information provides the full name,
institute, ensemble size, and spatial resolution of these models. (To date, these are the only models that
provide outputs for both GHG and NAT experiments.) In addition, we utilized 30 members produced by
Geophysical Research Letters
Key Points:
Increased GHG affects the May 2015
oods in Texas
Climate warming intensies the El Niño
teleconnection and climate impacts
Amplied synoptic waves and
strengthened LLJ are part of
climate trends
Supporting Information:
Text S1, Figures S1S3,
and Tables S1 and S2
Correspondence to:
S.-Y. Simon Wang,
Simon Wang, S.-Y., W.-R. Huang, H.-H.
Hsu, and R. R. Gillies (2015), Role of the
strengthened El Niño teleconnection in
the May 2015 oods over the southern
Great Plains, Geophys. Res. Lett., 42,
Received 4 JUL 2015
Accepted 5 AUG 2015
Accepted article online 7 AUG 2015
©2015. The Authors.
This is an open access article under the
terms of the Creative Commons
License, whic h permits use and distri-
bution in any medium, provided the
original work is properly cited, the use is
non-commercial and no modications
or adaptations are made.
the Community Earth System Model version 1 (CESM1) through the Large Ensemble Project (LEP) [Kay et al.,
2014]. The CESM1 ensemble simulations covered two periods: 19202005 with ALL forcing and 20062080
with RCP8.5 forcing (the total increase of radiative forcing at 8.5 W/m
/yr since preindustrial values). The
CESM1 was used here because it simulates well the ENSO cycle and associated teleconnection in North
America [Wang et al., 2014, 2015]. All model outputs were regridded to 2.5° longitude × 2.5° latitude resolution
before averaging, to be comparable with the National Centers fo r Environmental Predic tion (NCEP)/
National Center for Atmospheric Research Rean alysis (R1) data [Kalnay et al., 1996]. Although the R1 is an
older-generation reanalysis, it is the only data set that covers the presatellite era (before 1979) and yet is still
updated operationally. Meanwhile, we utilized four satellite era reanalyses to establish a consensus for the
trend analysis, including MERRA [Rienecker et al., 2011], CFSR [Saha et al., 2010], ERA-Interim [Dee et al.,
2011], and the JRA-25 [Onogi et al., 2007], detailed in Table S2. These reanalyses were averaged with equal
weighting to form an ensemble, following Wang et al. [2013]. Other data sets included were the Extended
Reconstructed Sea Surface Temperature (v3b) derived from the International Comprehensive Ocean-
Atmosphere Data Set [Smith and Reynolds, 2003] and global precipitation produced by NOAAs
Precipitation Reconstruction over Land (PREC/L) and historical observations over ocean (PREC/O); these
commence from 1948 [Chen et al., 2002]. The denition of ENSO was determined by the monthly mean
Niño3.4 index provided by the Climate Prediction Center (CPC).
3. Results
3.1. El Niño Factor
As shown in Figure 1c, the May 2015 anom aly of the 250 hPa stream function ( as a departure from the
19812010 mean) depicts a standing trough o ver the southwest U.S.; this trough directed a series of
Figure 1. (a) SST anomaly (°C) of 615 May 2015 obtained from
(b) May 2015 precipitation anomaly in millimeters obtained from (c) 250 hPa stream
function anomaly (ψ; shadings) and 850 hPa anomalous winds (vectors, m/s) of May 2015 derived from NCEP1 Reanalysis;
the black contours outline ±12 × 10
Geophysical Research Letters
short waves toward Texas and Oklahoma
(not shown). The 850 hPa wind anomalies
(vector) depict the intensied southerly
ow that conveyed moisture from the
Gulf of Mexico into the Great Plains; these
upper and lower level features indicate a
coupling of baroclinic (frontal) forcing
and moisture supply and are of climatolo-
gical importance in sustaining late-spring
rainfall in the southern Great Plains
[Helfand and Schubert, 1995; Higgins
et al., 1997; Santanello et al., 2012].
Additionally, as shown in Figure 1c, the
anomalous trough over the southwest
U.S. was accompanied by a subtropical
anticyclone in the eastern Pacic; this
formed a teleconnection pattern that
resembles the atmospheric response to
equatorial eastern Pacic sea surface tem-
perature (SST) forcing [e.g., Mo, 2010].
Daily rainfall data over Texas and
Oklahoma (not shown) indicated that
the entire month of May, with the
exception of 13 and 12 May, experi-
enced consecutively large rainfall totals.
The coexistence of an El Niño with large
May rainfall echoes the observation of
S.-K. Lee et al. [2014] that a positive
precipitation anomaly centered over
Texas tends to occur in late spring during
the onset of an El Niño; this is coincident
with CPCs announcement of 2015 El
Niño advisory in March (i.e., issued when
El Niño conditions are observed and
expected to build) so that by the time May came around, the warm-tongue SST pattern (Figure 1a) had
transitioned toward an El Nino onset.
To examine the long-term change in the relationship between the ENSO teleconnection and precipitation
anomalies in the southern U.S., we regressed the May Niño3.4 index with the monthly mean precipitation
for two periods: 19481980 (Figure 2a) and 19812014 (Figure 2b, unit: mm/month/C)). Here all the data
within either period were linearly detrended to minimize the effect of any interdecadal trends or cycles.
While the east-west contrast between a wetter Great Plains and drier southeast is apparent in both periods,
the regressed precipitation over Texas and Oklahoma exhibits a distinctively stronger signal in the latter time
period. Next, the role of increased GHG in the atmosphere in the ENSO-precipitation relationship was
analyzed by conducting the regression analysis for CMIP5s NAT-only (Figure 2c) and GHG-only (Figure 2d)
experiments, covering the period 19702005. Despite differences in the general precipitation pattern as com-
pared to observations (a result of inherent model biases), the GHG-only forcing produces a signicantly stron-
ger precipitation response over Texas and Oklahoma. Moreover, a similar analysis performed using the CESM1
LEP data for the periods of 19401980 (Figure 2e) and 20102050 (Figure 2f; i.e., that reects future precipitation
outcomes) reveals the same tendency, i.e., stronger precipitation anomalies over Texas and Oklahoma in
response to a transformational ENSO signature in a warmer climate. Noteworthy here is that since CESM1
is not included in the 17 CMIP5 models, this result also serves to validate the multimodel analysis.
Since the regression is linear, the corollary is validthat is, the La Niña-induced precipitation decit or drought
would likewise result over Texas and Oklahoma and equally so, any overtones associated with a strong La Niña
Figure 2. May precipitation regression with Niño3.4 index for (a)
19481980 and (b) 19812014; values exceeding ±9 are signicant at the
95% interval (unit: mm/month/C). The high-precipitation region in Texas
and Oklahoma is outlined with the white dashed line. (c and d) Same as
Figures 2a and 2b except for the ensembles of CMIP5 historical experi-
ments from the NAT-only and GHG-only forcing experiments, respectively,
over the 19702005 period. Purple contours outline the values of 23. (e and
f) Similar to Figures 2c and 2d except for the 30-member ensembles of
CESM1 for the 19401980 and 20102050 periods, respectively.
Geophysical Research Letters
as was the case in 2011 [Peterson et al., 2012]. In the future, as can be inferred from Figure 2f, one may anticipate
the tendency for an increased ENSO impact on the southern Great Plains precipitation regime.
Recent research [Meehl and Teng, 2007; Stevenson et al., 2012; Wang et al., 2015] indicates that ENSO teleconnec-
tion and its regional impact would intensify in response to increasing SST. Under such a premise we regressed
the 250 hPa stream function with the Niño3.4 index (Figure 3a) for the same two time periods as in Figure 2. The
ENSO-induced great arch teleconnection emanating from the central equatorial Pacic is visible in both
periods. However, the post-1980 time period features a noticeably stronger circulation amplitude; this includes
a deepened, standing trough west of Texas as in May 2015. The deepened trough, together with an abnormally
strong subtropical jet that extends into Baja California (not shown), is indicative of enhanced synoptic waves
directed toward the southern Great Plains. In Figures 3c and 3d we show the tropical precipitation (shaded)
Figure 3. Same as Figures 2a and 2b except for (a, b) the observed 250 hPa stream function anomalies ψ (contours for ±5)
and (c, d) global precipitation (shadings) and SSTA (contours for 0.4, 0.6, and 0.85°C) in May. Here the Niño3.4 index was
standardized so the variables reect their native unit. (e and f) May SST means of the two periods with a single contour of
28.5°C encircling the warm pool. The yellow ovals indicate the precipitation anomaly center based upon the 19812014
period. Contours in Figures 3a and 3b outline 5 × 10
which cover the 99% condence interval.
Geophysical Research Letters
and SST (contoured) regressions during the different time periods: After 1980, the El Niño-induced pre-
cipitation and SST anomalies r eveal marked increases over the equatorial central Pacicin fact, at the
center (outlined by a yellow circle), precipitation has increased 1.7 times in the latter period while the
mean SST increased by about C (Figur es 3e and 3f).
Focusing on wintertime, Zhou et al. [2014] found that the tropical Pacic precipitation anomalies associated
with ENSO would intensify in a warmer climate while extending eastward over the equatorial eastern basin.
Such an increase in precipitation, which is similar to what Figure 3d shows, leads to substantial change in
latent heating that can further intensify the teleconnection response [e.g., Branstator, 1985; Palmer, 2014;
Wang et al., 2015]. To examine further, we conducted a comparable analysis to that of Figure 3 but this time
with respect to the CMIP5 models in order to detect any change in the ENSO teleconnection between that of
NAT and GHG; this is shown in the supporting information Figure S1 for the time period 19702005. The results
are alike in that under CHG forcing, an intensied teleconnection wave train linked to a deepened trough in the
southwestern U.S. is observed, in association with precipitation anomaly enhancement over the equatorial cen-
tral Pacic. Altogether, the results presented here (i.e., Figures 2 and 3) as well as those in the current literature
support the strengthening of the ENSO teleconnection due to a warmer climate.
3.2. Other Factors
The cause of widespread ooding is manifold and cannot be explained solely by any single climate process.
Additional circulation features associated with the extreme rainfall of May 2015 do exist: By conducting a
power spectral analysis for zonal wave numbers in the May 2015 stream function within the 30°50°N latitu-
dinal zone, a wave 2 regime and a wave 5 regime emerged (see Figure S2). While the wave 2 regime reects
the ENSO-induced circulation anomaly that is inherently of longer wavelength [Wallace and Gutzler, 1981],
the wave 5 regime echoes an increasingly inuential mode of the so-called circumglobal teleconnection
[Branstator, 2002; Schubert et al., 2011; Teng et al., 2013]. Focusing on the latter, we performed a zonal harmo-
nic analysis on the stream function anomaly following Wang et al. [2013]; this wave 5 component is shown in
Figure 4a. A clear short-wave train emerges encompassing the deepened trough west of the ooded region
and the anomalous ridge to the east. We next computed the linear trend (slope) of this wave 5 stream func-
tion for the time period of 19802014 from the ensemble of modern-era reanalyses; this is shown in
Figure 4. (a) The 250 hPa stream function anomalies of May 2015 in the wave 5 regime overlaid with the climatological jet
stream (hatched; |V| > 25 m/s); the yellow-red domain indicates the Texas-Oklahoma oods. (b) Linear trend (total change
over the 19812014 period) of the wave 5 regime stream function (unit: 10
) computed from the ensemble of four
satellite era reanalyses, with the 95% condence interval shaded. Notice the phase coincidence between Figures 4a and 4b.
(c) Same as Figure 4b but for the column water vapor ux (formula indicated, where g is gravity, q is specichumidity,p
is pressure, and V is horizontal winds). Southerly component is colored with the red scale.
Geophysical Research Letters
Figure 4b. The trend reveals a distinct wave pattern in the wave 5 regime, and the phase of this intensied
short-wave train is remarkably coincident with the May 2015 anomaly. This result suggests an intensication
of the short-wave circulation and is resonant with the ndings of Meehl and Teng [2007] and J.-Y. Lee et al.
[2014], i.e., that increased ENSO amplitude that ensues from a warmer climate produces a prominent wave
5 pattern within the teleconnection.
The similarity between the two wave 5 circulations (Figures 4a and 4b) accompanied by a stronger low-level
jet (LLJ) in the Great Plains (Figure 1c) implies a coupling enhancement in the classic trough-LLJ setting
[Uccellini, 1980], and such coupling produces the majority of precipitation in the southern Great Plains during
the late spring [Wang and Chen, 2009]. Readers are referred to Text S1 for further explanation of the relevant
synoptic processes. The long-term change in this trough-LLJ coupling was further examined by computing
the linear trend of the column water vapor uxes QðÞ, integrated up to 300 hPa (Figure 4c). A distinct band
of southerly Q forms over the southern Great Plains signifying an intensied LLJ that is coupled with the dee-
pened upper level trough to the west, as was noted in Barandiaran et al. [2013]. While Weaver et al. [2009]
related the springtime LLJ intensication to interdecadal variation in the North Atlantic, Cook et al. [2008]
linked the increased LLJ with the anthropogenic global warming.
Though the cause of ood is not the focus here, a nal comment that should be realized is that ground con-
ditions in Texas more than likely were preconditioned to initiate ooding conditions (J. Meng, NOAA/NCEP/
EMC, personal communication, 2015): As Figure S3 shows, April 2015 was abnormally wet in southern Texas
(though not exceptionally) whereupon soil moisture in the Huston area was already above normal for that
time of year which carried forward into early May near saturation conditions.
4. Summary
The record precipitation that occurred over Texas and Oklahoma during the month of May 2015 was the
result of a series of climate interactions and anomalies. Foremost is the role that ENSO played: A developing
El Niño has a tendency to increase spring precipitation over the southern Great Plains, and this effect was
found to have intensied since 1980; this intensication was concomitant with a warmer atmosphere due
to anthropogenic GHG. Specically, the intensied ENSO teleconnection appears to be triggered by
enhanced latent heating in the equatorial central Pacic and is associated with broad SST warming in the tro-
pics. In essence, there was a detectable effect of anthropogenic global warming on the teleconnection and
moisture transport leading to May 2015s high precipitation. Previous studies as well as this one point to
the following processes: (1) long-term warming of the tropical Pacic acting to strengthen the atmospheric
response to ENSO, (2) El Niño modulating the wave 5 circulation pattern in a warmer climate and its phase
lock with the May 2015 anomaly, (3) enhancement of the Great Plains LLJ and associated moisture supply
in late spring, and (4) the LLJs coupling with the deepened spring trough at upper levels. All the aforemen-
tioned processes together with the attribution analyses of CMIP5 and CESM1 models analyzed here point
toward the exacerbating effect of increasing GHG on the springtime precipitation over Texas and
Oklahoma during a developing El Niñothis being so currently (i.e., 2015) and in the future. Furthermore,
the diagnostic analyses detailed here, in which increased extreme events and a warmer climate were shown
to be dynamically linked, are keys in the provision of seasonal predictions as a guide to future occurrences
and intensities of extreme weather events.
Barandiaran, D., S.-Y. Wang, and K. Hilburn (2013), Observed trends in the Great Plains low-level jet and associated precipitation changes in
relation to recent droughts, Geophy. Res. Lett., 40, 62476251, doi:10.1002/2013GL058296.
Branstator, G. (1985), Analysis of general circulation model sea-surface temperature anomaly simulations using a linear model. Part I: Forced
solutions, J. Atmos. Sci., 42, 22252241.
Branstator, G. (2002), Circumglobal teleconnections, the jet stream waveguide, and the North Atlantic Oscillat ion, J. Clim., 15, 18931910.
Chen, M., P. Xie, J. E. Janowiak, and P. A. Arkin (2002), Global land precipitation: A 50-yr monthly analysis based on gauge observations,
J. Hydrometeo rol., 3, 249266.
Cook, K. H., E. K. Vizy, Z. S. Launer, and C. M. Patricola (2008), Springtime intensication of the Great Plains low-level jet and midwest
precipitation in GCM simulations of the twenty-rst century, J. Clim., 21, 63216340.
Dee, D. P., et al. (2011), The ERA-Interim reanalysis: Conguration and performance of the data assimilation system, Q. J. R. Meteorol. Soc., 137,
Helfand, H. M., and S. D. Schubert (1995), Climatology of the simulated Great Plains low-level jet and its contribution to the continental
moisture budget of the United States, J. Clim., 8, 784806.
Soil moisture information shared by Jesse
Meng is appreciated. W.-R. Huang was
supported by the Ministry of Science and
Technology of Taiwan under MOST 104-
2111-M-003-001 and MOST 103-2111-M-
003-001. H.-H. Hsu is supported by NSC
100-2119-M-001-029-MY5 supported by
MOST, Taiwan. S.-Y. Wang and R.R. Gillies
are supported by the Bureau of
Reclamation grants R11AC81456 and
R13AC80039. ENSO indices are provided
by the CPC at http://www.cpc.ncep.noaa.
gov/data/indices/sstoi.indices. All data
utilized in this study are freely available
from the following sources: the
NOAA/OAR/ESRL PSD, Boulder, Colorado,
USA, from their Web site at http://www., the CMIP5 Data Portal
data_portal.html, and the CESM1 Large
Ensemble Community Project at http://
The Editor thanks two anonymous
reviewers for their assistance in
evaluating this paper.
Geophysical Research Letters
Higgins, R., Y. Yao, E. Yarosh, J. E. Janowiak, and K. Mo (1997), Inuence of the Great Plains low-level jet on summertime precipitation and
moisture transport over the central United States, J. Clim., 10, 481507.
Kalnay, E., et al. (1996), The NCEP/NCAR 40-year reanalysis project, Bull. Am. Meteorol. Soc., 77, 437471.
Kay, J. E., et al. (2014), The Community Earth System Model (CESM) Large Ensemble Project: A community resource for studying climate
change in the presence of internal climate varia bility, Bull. Am. Meteorol. Soc., doi:10.1175/BAMS-D-13-00255.1.
Lee, J.-Y., B. Wang, K.-H. Seo, J.-S. Kug, Y.-S. Choi, Y. Kosaka, and K.-J. Ha (2014), Future change of Northern Hemisphere summer tropical
extratropical teleconnection in CMIP5 models, J. Clim., 27, 36433664.
Lee, S.-K., B. E. Mapes, C. Wang, D. B. Eneld, and S. J. Weaver (2014), Springtime ENSO phase evolution and its relat ion to rainfall in the
continental U.S, Geophys. Res. Lett., 41, 16731680, doi:10.1002/2013GL059137.
Meehl, G. A., and H. Teng (2007), Multi-model changes in El Niño teleconnections over North America in a future warmer climate, Clim. Dyn.,
29, 779790.
Meehl, G. A., et al. (2014), Decadal climate prediction: An update from the trenches, Bull. Am. Meteorol. Soc., 95, 243267.
Mo, K. C. (2010), Interdecadal modulation of the impact of ENSO on precipitation and temperature over the United States, J. Clim. , 23,
Onogi, K., et al. (2007), The JRA-25 reanalysis, J. Meteorol. Soc. Jpn. Ser. II, 85, 369432.
Palmer, T. (2014), Record-breaking winters and global climate change, Science, 344, 803804.
Peterson, T. C., P. A. Stott, and S. Herring (2012), Explaining extreme events of 2011 from a climate perspective, Bull. Am. Meteorol. Soc., 93,
Rienecker, M. M., et al. (2011), MERRA: NASAs Modern-Era Retrospective Analysis for Research and Applications, J. Clim., 24, 36243648,
Ropelewski, C. F., and M. S. Halpert (1986), North American precipitation and temperature patterns associated with the El Niño/Southern
Oscillation (ENSO), Mon. Weather Rev., 114, 2352
Ropelewski, C. F., and M. S. Halpert (1987), Global and regional scale precipitati on patterns associated with the El Niño/Southern Oscillation,
Mon. Weather Rev., 115, 16061626.
Saha, S., et al. (2010), The NCEP Climate Forecast System Reanalysis, Bull. Am. Meteorol. Soc., 91, 10151057.
Santanello, J. A., C. D. Peters-Lidard, A. Kennedy, and S. V. Kumar (2012), Diagnosing the nature of landatmosphere coupling: A case study of
dry/wet extremes in the U.S. Southern Great Plains, J. Hydrometeorol., 14,324.
Schubert, S., H. Wang, and M. Suarez (2011), Warm season subseasonal variability and climate extremes in the Northern Hemisphere: The role
of stationary Rossby waves, J. Clim., 24, 47734792.
Smith, T. M., and R. W. Reynolds (2003), Extended reconstruction of global sea surface temperatures based on COADS data (18541997),
J. Clim., 16, 14951510.
Stevenson,S.,B.Fox-Kemper,M.Jochum,R.Neale,C.Deser,andG.Meehl(2012),Willtherebeasignicant change to El Niño in the
twenty-rst ce n tury ? , J. Clim., 25, 21292145.
Taylor, K. E., R. J. Stouffer, and G. A. Meehl (2011), An overview of CMIP5 and the experiment design, Bull. Am. Meteorol. Soc., 93, 485498.
Teng, H., G. Branstator, H. Wang, G. A. Meehl, and W. M. Washington (2013), Probability of US heat waves affected by a subseasonal planetary
wave pattern, Nat. Geosci. , 6, 1056 1061.
Uccellini, L. W. (1980), On the role of upper tropospheric jet streaks and leeside cyclogenesis in the development of low-level jets in the Great
Plains, Mon. Weather Rev., 108, 16891696.
Wallace, J. M., and D. S. Gutzler (1981), Teleconnections in the geopotential height eld during the Northern Hemisphere winter, Mon.
Weather Rev., 109, 784 812.
Wang, S.-Y., and T.-C. Chen (2009), The late-spring maximum of rainfall over the U.S. Central Plains and the role of the low-level jet, J. Clim., 22,
Wang, S.-Y., R. E. Davies, and R. R. Gillies (2013), Identication of extreme precipitation threat across midlatitude regions based on short-wave
circulations, J. Geophys. Res. Atmos.,
118, 11,05911,074, doi:10.1002/jgrd.50841.
Wang, S.-Y., L. Hipps, R. R. Gillies, and J.-H. Yoon (2014), Prob able causes of the abnormal ridge accompanying the 20132014 California
drought: ENSO precursor and anthropogenic warming footpr int, Geophy. Res. Lett., 41, 32203226, doi:10.1002/2014GL059748.
Wang, S.-Y., W.-R. Huang, and J.-H. Yoon (2015), The North American winter dipole and extremes activity: A CMIP5 assessment, Atmos. Sci.
Lett., 16, 338345, doi:10.1002/asl2.565.
Weaver, S. J., S. Schubert, and H. Wang (2009), Warm season variations in the low-level circulation and precipitation over the central United
States in observations, AMIP simulations, and idealized SST experiments, J. Clim., 22, 54015420.
Zhou, Z.-Q., S.-P. Xie, X.-T. Zheng, Q. Liu, and H. Wang (2014), Global warminginduced changes in El Niño telecon nections over the North
Pacic and North America, J. Clim., 27, 90509064.
Geophysical Research Letters
... The weather in 2015 presented another confounding factor. Spring and summer rains in 2015 caused widespread flooding throughout Clay County after 4 years of extreme drought (Wang et al. 2015). Some data points were inaccessible for days or weeks. ...
... Consequently, this MCS cluster caused ∼45 million U.S. dollars of flood damage in Houston alone (AP 2015) and substantial losses in life and properties in surrounding areas including Oklahoma and Louisiana due to flash and extensive floods and even tornados associated with the clustered MCSs. This case has been linked with the persistent and strengthened El Niño sea surface temperature pattern that deepened the stationary trough west of Texas and enhanced the Great Plains low-level jet and further attributed to the warming climate (Wang et al. 2015). Sharing similar favorable large-scale atmospheric dynamic and thermodynamic conditions, multiple MCSs may develop and interact with each other through modulation of their common large-scale environment to form an MCS cluster. ...
Mesoscale convective systems (MCSs) that are clustered in time and space can have a broader impact on flooding because they have larger area coverage than that of individual MCSs. The goal of this study is to understand the flood likelihood associated with MCS clusters. To achieve this, floods in the Storm Events Database in April–August of 2007–17 are matched with clustered MCSs identified from a high-resolution MCS dataset and terrestrial conditions in a land surface dataset over the central-eastern United States. Our analysis indicates that clustered MCSs preferentially occurring in April–June are more effective at producing floods, which also last longer due to the greater rainfall per area and wetter initial soil conditions and, hence, produce greater runoff per area than nonclustered MCSs. Similar increases of flood occurrence with cluster-total rainfall size and wetter soils are also observed for each MCS cluster, especially for the overlapping rainfall areas within each cluster. These areas receive rainfall from multiple MCSs that progressively wet the soils and are therefore associated with higher flood likelihood. This study underscores the importance to understand clustered MCSs to better understand flood risks and their future changes.
... ENSO is also influenced by drought as in projections of future groundwater drought [353], drought and climate teleconnection [354], in Iran [355], China [345], as well as a series of droughts in the USA in 1988 [356], Further works address the turn of the century [357], droughts in general [358], in mainland Southeast Asia [359], in Northern Chile [360] and East African drought during rainy seasons [361]. Flood occurrence is influenced as well shown by the 2010 Pakistan flood and the Russian heat wave [362], as well as in Iran's Kan River basin [363], in the Southern Great Plains [364], the Missouri River Basin [365], the Yangtze River [366] and on a global level [367]. There is also extreme precipitation in North America [368], Central-Eastern China [369], over China in general [370], as part of the ENSO asymmetric effect [371], and in Northern South America [372]. ...
... ENSO is also influenced by drought as in projections of future groundwater drought [353], drought and climate teleconnection [354], in Iran [355], China [345], as well as a series of droughts in the USA in 1988 [356], Further works address the turn of the century [357], droughts in general [358], in mainland Southeast Asia [359], in Northern Chile [360] and East African drought during rainy seasons [361]. Flood occurrence is influenced as well shown by the 2010 Pakistan flood and the Russian heat wave [362], as well as in Iran's Kan River basin [363], in the Southern Great Plains [364], the Missouri River Basin [365], the Yangtze River [366] and on a global level [367]. There is also extreme precipitation in North America [368], Central-Eastern China [369], over China in general [370], as part of the ENSO asymmetric effect [371], and in Northern South America [372]. ...
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An analytical review of physical blue and green water scarcity in terms of agricultural use, and its amenability to economic interpretation, is presented, employing more than 600 references. The main definitions and classifications involved and information about reserves and resources are critically analyzed, blue and green water scarcity are examined along with their interchange, while their causal connection with climate in general is analyzed along with the particular instances of Europe, Africa, Asia and the WANA region. The role of teleconnections and evaporation/moisture import-export is examined as forms of action at a distance. The human intervention scarcity driver is examined extensively in terms of land use land cover change (LULCC), as well as population increase. The discussion deals with following critical problems: green and blue water availability, inadequate accessibility, blue water loss, unevenly distributed precipitation, climate uncertainty and country level over global level precedence. The conclusion singles out, among others, problems emerging from the inter-relationship of physical variables and the difficulty to translate them into economic instrumental variables, as well as the lack of imbedding uncertainty in the underlying physical theory due to the fact that country level measurements are not methodically assumed to be the basic building block of regional and global water scarcity.
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Central Oklahoma is undergoing investment in new intermodal transportation and rehabilitation of its infrastructure. Despite a highly variable historical climate, future changes resulting from anthropogenic climate change may be outside of the range for which infrastructure was designed. We examined 21st century trends, focusing on weather and climate extremes of demonstrated importance to transportation professionals as identified through expert input. We assessed trends from a suite of 15 global climate models (GCMs) using two emissions scenarios and two high-resolution statistically downscaled datasets. This ensemble provided a quantitative range for potential future climate conditions whilst revealing uncertainties associated with different models and downscaling methods. Our results support the general consensus of a reduction in the frequency of cold temperatures, freeze–thaw cycles, and winter weather; however, for the latter, there is not necessarily a reduction in intensity. Extreme heat days (e.g., days ≥100 °F) increased by factors of 3–6, with this upper range associated with high greenhouse gas emissions, while the seasonal duration of extreme heat extended by 4–10 weeks. Projected return intervals for heavy rainfall increased in frequency and magnitude in the mid and late 21st century. Although the contribution of the emissions pathway to these changes is evident, different extreme value distributions and the varying simulations of precipitation from the GCMs have a large effect on magnitudes, leading to a range of possible futures to consider in infrastructure design. Precipitation metrics, particularly at the extremes, were more sensitive to the selection of downscaled data, as compared with temperature metrics. Our approach represents a resource for transportation professionals seeking to identify changing risk probabilities at regional to local scales, as a precursor to planning and adaptation.
Flood is one of the most dangerous natural hazards in India due to their devastating effects in every sector. The present study was designed to develop flood-susceptible map using geospatial-based AHP method in Teesta River basin of West Bengal, India. At first, we selected ten flood factors such elevation, slope, TPI, SPI, NDVI, drainage density, mean annual rainfall, MNDWI, lithology, and distance from the river for developing flood susceptibility map. The most important flood influencing factors were elevation (27%), slope (19%), distance from the river (14%), and drainage density (14%). The obtained suitability map identified 11.99%, 13.90%, 21.48%, 23.93%, and 28.70% of study areas as very high, high, moderate low, and very low susceptible areas, respectively. The accuracy of flood susceptibility map was tested using ROC and AUC analysis. The obtained AUC value was 0.739, confirming the reliability of applied method in flood modeling. The finding of this study will be useful in preparing the effective flood management strategies.
It is well established that the climate is changing and much of the change is as a result of human greenhouse gas emissions. Effective strategies for adaptation or mitigation are less agreed on. From an engineering perspective, adaptation strategies require reliable expectations of the climate changes expected over the lifetime of current projects. Such projections are now possible with state-of-the-art observations and computer models that provide information over the next century and beyond. The best estimates suggest that global surface temperatures will increase by approximately 5°C (9°F) over pre-industrial temperatures or approximately 4°C (7°F) over current temperatures by the year 2100.
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Recent research has linked the climate variability associated with ocean-atmosphere teleconnections to impacts rippling throughout environmental, economic, and social systems. This research reviews recent literature through 2021 in which we identify linkages among the major modes of climate variability, in the form of ocean-atmosphere teleconnections, and the impacts to temperature and precipitation of the South-Central United States (SCUSA), consisting of Arkansas, Louisiana, New Mexico, Oklahoma, and Texas. The SCUSA is an important areal focus for this analysis because it straddles the ecotone between humid and arid climates in the United States and has a growing population, diverse ecosystems, robust agricultural and other economic sectors including the potential for substantial wind and solar energy generation. Whereas a need exists to understand atmospheric variability due to the cascading impacts through ecological and social systems, our understanding is complicated by the positioning of the SCUSA between subtropical and extratropical circulation features and the influence of the Pacific and Atlantic Oceans, and the adjacent Gulf of Mexico. The Southern Oscillation (SO), Pacific-North American (PNA) pattern, North Atlantic Oscillation (NAO) and the related Arctic Oscillation (AO), Atlantic Multidecadal Oscillation/Atlantic Multidecadal Variability (AMO/AMV), and Pacific Decadal Oscillation/Pacific Decadal Variability (PDO/PDV) have been shown to be important modulators of temperature and precipitation variables at the monthly, seasonal, and interannual scales, and the intraseasonal Madden-Julian Oscillation (MJO) in the SCUSA. By reviewing these teleconnection impacts in the region alongside updated seasonal correlation maps, this research provides more accessible and comparable results for interdisciplinary use on climate impacts beyond the atmospheric-environmental sciences.
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Estimation of economic loss is essential for stakeholders to manage flood risk. Most flooding events are closely related to extreme precipitation, which is influenced by large-scale climate factors. Considering the lagged influence of climate factors, we developed a flood-risk assessment framework and used Hunan Province in China as an example to illustrate the risk assessment process. The main patterns of precipitation-as a connection between climate factors and flood economic losses-were extracted by the empirical orthogonal function (EOF) analysis. We identified the correlative climate factors through cross-correlation analysis and established a multiple stepwise linear regression model to forecast future precipitation patterns. Risk assessment was done based on the main precipitation patterns. Because the economic dataset is limited, a Monte Carlo simulation was applied to simulate 1000-year flood loss events under each precipitation regime (rainy, dry, normal years) to obtain aggregate exceedance probability (AEP) and occurrence exceedance probability (OEP) curves. We found that precipitation has a strong influence on economic loss risk, with the highest risk in rainy years. Regional economic development imbalances are the potential reason for the varying economic loss risks in different regions of Hunan Province. As the climate indices with at least several months prediction lead time are strong indicators in predicting precipitation, the framework we developed can estimate economic loss risk several months in advance.
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The hypothesis of this study was one of existence of spatially organized links between the time series of river runoff and climate variability indices, describing the oscillations in the atmosphere–ocean system: ENSO (El Niño–Southern Oscillation), PDO (Pacific Decadal Oscillation), AMO (Atlantic Multidecadal Oscillation), and NAO (North Atlantic Oscillation). The global river flow reconstructions (ERA-20-CM-R) for 18 study areas on six continents and climate variability indices for the period 1901–2010 were used. The split-sample approach was applied, with the period 1901–2000 used for training and 2001–2010 used for testing. The quality measures used in this paper were mean absolute error, dynamic time warping, and top extreme events error. We demonstrated that a machine learning approach (convolution neural network, CNN) trained on climate variability indices can model the river runoff better than the long-term monthly mean baseline, both in univariate (per-cell) and multivariate (multi-cell, regionalized) settings. We compared the models to the baseline in the form of heatmaps and presented results of ablation experiments (test time ablation, i.e., jackknifing, and training time ablation), which suggested that ENSO is the primary determinant among the considered indices.
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El Niño-Southern Oscillation (ENSO) induces climate anomalies around the globe. Atmospheric general circulation model simulations are used to investigate how ENSO-induced teleconnection patterns during boreal winter might change in response to global warming in the Pacific-North American sector. As models disagree on changes in the amplitude and spatial pattern of ENSO in response to global warming, for simplicity the same sea surface temperature (SST) pattern of ENSO is prescribed before and after the climate warming. In a warmer climate, precipitation anomalies intensify and move eastward over the equatorial Pacific during El Niño because the enhanced mean SST warming reduces the barrier to deep convection in the eastern basin. Associated with the eastward shift of tropical convective anomalies, the ENSO-forced Pacific-North American (PNA) teleconnection pattern moves eastward and intensifies under the climate warming. By contrast, the PNA mode of atmospheric internal variability remains largely unchanged in pattern, suggesting the importance of tropical convection in shifting atmospheric teleconnections. As the ENSO-induced PNA pattern shifts eastward, rainfall anomalies are expected to intensify on the west coast of North America, and the El Niño-induced surface warming to expand eastward and occupy all of northern North America. The spatial pattern of the mean SST warming affects changes in ENSO teleconnections. The teleconnection changes are larger with patterned mean warming than in an idealized case where the spatially uniform warming is prescribed in the mean state. The results herein suggest that the eastward-shifted PNA pattern is a robust change to be expected in the future, independent of the uncertainty in changes of ENSO itself.
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The 2013-2014 winter in North America brought intense drought in the West and severe cold in the East. The circulation anomalies were characterized as a dipole: an amplified upper-level ridge over the West Coast and a deepened trough over the central-eastern U.S. A previous study using a single model has linked the dipole to the El Niño precursor and found that this link has strengthened in recent years. Here, 17 models from the Coupled Model Intercomparison Project Phase 5 are utilized to examine the dipole activity. Most models capture the dipole and its association with El Niño precursor and project this association to strengthen.
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While internal climate variability is known to affect climate projections, its influence is often underappreciated and confused with model error. Why? In general, modeling centers contribute a small number of realizations to international climate model assessments (e.g., Coupled Model Intercomparison Project 5 (CMIP5)). As a result, model error and internal climate variability are difficult, and at times impossible, to disentangle. In response, the Community Earth System Model (CESM) community designed the CESM Large Ensemble (CESM-LE) with the explicit goal of enabling assessment of climate change in the presence of internal climate variability. All CESM-LE simulations use a single CMIP5 model (CESM with the Community Atmosphere Model version 5). The core simulations replay the 20–21st century (1920–2100) 30 times under historical and Representative Concentration Pathway 8.5 external forcing with small initial condition differences. Two companion 1000+-year long pre-industrial control simulations (fully coupled, prognostic atmosphere and land only) allow assessment of internal climate variability in the absence of climate change. Comprehensive outputs, including many daily fields, are available as single-variable time series on the Earth System Grid for anyone to use. Early results demonstrate the substantial influence of internal climate variability on 20th–21st century climate trajectories. Global warming hiatus decades occur, similar to those recently observed. Internal climate variability alone can produce projection spread comparable to that in CMIP5. Scientists and stakeholders can use CESM-LE outputs to help interpret the observational record, to understand projection spread, and to plan for a range of possible futures influenced by both internal climate variability and forced climate change.
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The 2013-14 California drought was accompanied by an anomalous high-amplitude ridge system. The anomalous ridge was investigated using reanalysis data and the Community Earth System Model (CESM). It was found that the ridge emerged from continual sources of Rossby wave energy in the western North Pacific starting in late summer, and subsequently intensified into winter. The ridge generated a surge of wave energy downwind and deepened further the trough over the northeast U.S., forming a dipole. The dipole and associated circulation pattern is not linked directly with either ENSO or Pacific Decadal Oscillation; instead it is correlated with a type of ENSO precursor. The connection between the dipole and ENSO precursor has become stronger since the 1970s, and this is attributed to increased GHG loading as simulated by the CESM. Therefore, there is a traceable anthropogenic warming footprint in the enormous intensity of the anomalous ridge during winter 2013-14, the associated drought and its intensity.
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Springtime ENSO phase evolution and associated U.S. rainfall variability is explored by performing composite analysis of observational data. Although the tropical Pacific ENSO SST anomalies are weaker and less coherent in boreal spring compared to those in winter, there are unique and significant patterns of U.S. rainfall anomalies frequently appearing during the onset and decay phases of ENSO. In early spring of a decaying El Niño, the atmospheric jet stream and associated storm track shift southward, causing more frequent wet conditions across the southern U.S. and dry conditions in a belt south and east of the Ohio River. In late spring of a developing El Niño, synoptic activity over the U.S. reduces overall and the southwesterly low-level winds that carry moist air from the Gulf of Mexico to the U.S. shift westward, causing a similar dipole of rainfall anomalies between the southern U.S. and the Ohio Valley.
Contemporaneous correlations between geopotential heights on a given pressure surface at widely separated points on earth, referred to as teleconnections in this paper, are studied in an attempt to identify and document recurrent spatial patterns which might be indicative of standing oscillations in the planetary waves during the Northern Hemisphere winter, with time scales on the order of a month or longer. -from Authors
A review of 15 cases of low level jets (LLJ) which developed in the Great Plains is presented. For 12 out of the 15 cases, a systematic upper level flow pattern was isolated which includes the existence of a trough over the southwest United States and the propagation of upper level jet streaks from the Rocky Mountains toward the Great Plains. This flow pattern is responsible for lee side cyclogenesis or lee side troughing that produces the pressure gradients needed for the development of the LLJ. For the other three cases, a blocking ridge existed over the Great Plains and the upper level flow is relatively weak. It is during these situations that the classic, diurnal oscillating LLJ was observed. A more detailed review of four cases indicates that the subsynoptic scale adjustments associated with the upper level jet streak's forcing of lee side cyclogenesis could be an important factor in the development of LLJ's in the Great Plains.
Just when it looked like spring was arriving this year, the U.S. Midwest slipped back into winter, and Detroit recorded its snowiest season ever (see the photo). Has global warming gone into reverse, or could human emissions of greenhouse gases actually be responsible for this particular record being broken? Although the chances of cold winters can in general be expected to decrease with global warming, climate change linked to the particular circulation patterns that have prevailed in the past decade or so could have played an important role in this record-breaking winter.