Here we provide information on ice columns and frozen rills found in late-season snowpacks in and near the Green Lakes Valleyofthe Colorado Front Range, USA. The presence of ice columns and frozen rills in late season snowpacks may provide insights with which to understand the spatial distribution of preferential flowpaths in melting snowpacks. In July and August of 1996 and 1997 we found ice columns in every one of the more than 50 snowfields we investigated. The ice columns showed a consistent morphology; each column was approximately 75 cm in vertical extent, with about 5 cm projecting above the snowsurface and 70 cm extending into the snowpack. An analysis of variance test shows that the 81 ice columns on the south-facing slopes were significantly greater than the 57 ice columns on the north-facing slope (p = 0.01). There were about 3 ice columns per square meter on the south facing slopes and 2 ice columns per square meter on the north-facing slopes. There was an interesting hysteresis in snowand ice temperatures that became stronger with increasing depth in adjacent thermocouple arrays. This hysteresis in the temperature profiles is consistent with the release of latent heat from the freezing of greater amounts of liquid water in and near the ice columns compared to the surrounding snowpack. At the Martinelli catchment, spacing between the frozen rills averaged 2.6 m(n=73). Weinterpret these "ribs" of solid ice to be the remnants of surface rills. Ve rtical ice columns were connected to these frozen rills. The ice columns and frozen rills may provide a snapshot or "schematic" diagram of the major flowpaths in a ripe and draining snowpack. Ice columns and frozen rills-3- Williams et al.
A new model of dispersion has been developed to simulate the impact of pollutant discharges on river systems. The model accounts for the main dispersion processes operating in rivers as well as the dilution from incoming tributaries and first-order kinetic decay processes. The model is dynamic and simulates the hourly behaviour of river flow and pollutants along river systems. The model has been applied to the Aries and Mures River System in Romania and has been used to assess the impacts of potential dam releases from the Roia Montan Mine in Transylvania, Romania. The question of mine water release is investigated under a range of scenarios. The impacts on pollution levels downstream at key sites and at the border with Hungary are investigated.
Nordic Hydrology, ISSN 0029-1277, vol. 26, nr. 1, 37-54 Acid sulphate (AS) soils cover extensive areas of the coastal plains in western Finland. These soils constitute an environmental hazard due to their ability to release acidity when exposed to atmospheric oxygen. Acidification of soil and water can be reduced or prevented if the factors influencing the release and transport of acidity in AS soils are known. The objective of this study was to develop mathematical models describing the acidity load from AS soils, thus providing tools for accurate soil and water management in the affected areas. The work resulted in a static and a dynamic model for predicting the runoff acidity from catchments containing AS soils. The main features of the models are described in the paper. Both models require significant catchment characteristics and hydrological monitoring results as input data, but no ion balance information is needed. Model applications showed that the static model is able to give good estimates of the mean acidity level to be expected during specific flood periods in the studied river, while the dynamic model, after calibration, is capable of predicting the daily acidity with appreciable accuracy. The information provided by the models can be used to assess adequate mitigation strategies for the watercourses affected by AS soils.
Nordic Hydrology, ISSN 0029-1277, vol. 26, nr. 1, 55-72 Nutrient losses from small drainage basins were compared to the nutrient fluxes in small coastal rivers in order to study the representativeness of the Finnish monitoring network of small basins, especially as regards agricultural loading to the Baltic Sea. Additionally flux estimates from the period 1986-1990 were compared to those of the period 1981-1985 in order to detect possible trends. The results suggest that in coastal regions with high proportions of agricultural land and with low lake percentage, the nutrient losses from agricultural areas mostly enter coastal waters with negligible retention in river channels. The net effect of the various processes in the rivers is small because most of the nutrient losses occur in spring, fall or early winter in connection with high water flows and current velocities, short residence times of water and low intensities of biogeochemical processes. Nitrogen losses from agriculture has probably increased during the 1980s due to increased winter flows and increased use of nitrogen fertilizers. The results indicate that nitrogen loading of the southern and south-western coastal waters of Finland has increased as well.
The application of three temperature-index based models and of one energy balance based snowmelt model was investigated. The snow models were integrated in the spatially distributed hydrological model PREVAH. In this study the hydrological simulations of the alpine catchment of the Dischmabach in Switzerland in the period 1982-2000 have been analyzed. The PREVAH model was driven by hourly interpolated meteorological data.
All snowmelt approaches allowed a good simulation of the discharge regime and of the seasonal course of the snowpack. The highest model efficiency was obtained by a radiation based temperature-index approach. A simplified energy balance approach combined with the positive degree-day method showed a very similar performance to the classical positive degree-day approach. The energy balance approach ESCIMO showed a high performance variability from year to year.
The dependency of the seasonal water balance with respect to altitude is also discussed in this report. The quality of the spatially distributed reproduction of periods with positive and negative water balance (snow accumulation and snowmelt) is crucial for the correct simulation of the runoff hydrograph. The analysis shows that runoff maximum in the Dischmabach catchment is caused by a superposition of the main snowmelt season in the areas between 2,100-2,800 m a.s.l. and the period with maximum rainfall.
Watershed scale hydrologic models require good estimates of the
spatially distributed snowpack at winter's end. Snow on the ground in
treeless Arctic environments is susceptible to significant wind
redistribution, which results in heterogeneous snowpacks, with greater
quantities of snow collection in depressions, valley bottoms and leeward
sides of ridges. In the Arctic, precipitation and snow gauges are very
poor indicators of the actual snowpack distribution. Snow distribution
patterns are similar from year to year because they are largely
controlled by the interaction of topography, vegetation, and consistent
weather patterns. From one year to the next, none of these controls
radically change. Consequently, shallow and deep areas of snow tend to
be spatially predetermined, resulting in depth (or SWE) differences that
may vary as a whole, but not relative to each other, from year to year.
We intend to identify snowpack distribution patterns and establish their
stability in time and space at a watershed scale in the Arctic. Snow
patterns are intended to be established in three ways: (1) numerous
field survey points from end of winter field campaigns, (2) through the
relationship between the snow and more easily established replacement
patterns like topography, and (3) by using remote sensing to produce
binary images of snow coved areas (SCA) and snow free (SF) areas during
ablation. The integration of all three pattern identification methods
will produce a hybrid approach to identifying snowpack distribution
patterns. Improvement in our estimates of the snowpack distribution will
aid in the forecasting of snowmelt runoff events, which are the most
significant hydrologic event of the year for larger Arctic watersheds.
The INtegrated CAtchment (INCA) model has been developed to simulate the impact of mine discharges on river systems. The model accounts for the key kinetic chemical processes operating as well as the dilution, mixing and redistribution of pollutants in rivers downstream of mine discharges or acid rock drainage sites. The model is dynamic and simulates the day-to-day behaviour of hydrology and eight metals (cadmium, mercury, copper, zinc, lead, arsenic, manganese and chromium) as well as cyanide and ammonia. The model is semi-distributed and can simulate catchments, sub-catchment and in-stream river behaviour. The model has been applied to the Roia Montan Mine in Transylvania, Romania, and used to assess the impacts of old mine adits on the local catchments as well as on the downstream Aries and Mures river system. The question of mine restoration is investigated and a set of clean-up scenarios investigated. It is shown that the planned restoration will generate a much improved water quality from the mine and also alleviate the metal pollution of the river system.
Hydrology Research Vol.41 Nr.3 - 4, 282 - 294 This paper examines the risk assessment procedure for a Nordic hydropower production process in the light of climate change. It is evident that climate change poses new risks and concerns for hydropower companies, especially with regards to high uncertainty that results from the ignorance of relationships between climate change and hydropower production (descriptive uncertainty). However, the climate change may also provide opportunities. This paper focuses on the development of a risk assessment procedure to support the risk identification process as a means of reducing the descriptive uncertainty. The intention of the study was to develop and test a procedure in which climate scenarios and traditional technical risk assessment have been integrated in order to obtain a practical method as well as associated support tools for identifying and evaluating climate change-related risks and opportunities for hydropower plants. This new procedure is meant to help hydropower plants to plan their future by identifying and prioritising the risks and opportunities caused by climate change. The study was conducted as a part of the Nordic Energy Research funded Climate and Energy Systems (CES) project and it was coordinated by VTT Technical Research Centre of Finland.
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A model for water exchange of a basin connected to the open sea by two channels has been worked out. The model is applied on the Gulf of Riga, where the water exchange processes versus strong landbased inflow of nutrients are the most important factors in formation of the trophic status of the Gulf.
The model's response both to stationary external conditions and nonstationary impulses (changes in the sea level, wind and riverine inflow) is analysed and possibilities for matter exchange calculations are discussed. It appeared that the water exchange depends strongly on the configuration and position of the straits. The water exchange in such a two-channel system is considerably different (and stronger) than in the case of a one-channel version. The main external force for the Gulf appeared to be the wind.
Records of discharge from partially-glacierised basins in the upper Rhône catchment, Switzerland, were examined together with air temperature and precipitation data in order to assess impacts of climatic fluctuation and percentage glacierisation of basin on runoff, as glaciers declined from dimensions attained during the Little Ice Age. Above 60% glacierisation, year-to-year variations in runoff mimicked mean May–September air temperature, rising in the warm 1940s, declining in the cool 1970s, before increasing (by 50%) into the warm dry 1990s/2000s but not reaching 1940s maxima. In basins with between 35–60% glacierisation, flow also increased into the 1980s but waned through the 1990s. With less than 2% glacierisation, the pattern of runoff was broadly the inverse of that of temperature and followed precipitation, dipping in the 1940s, rising in the cool wet late 1960s, and declining into the 1990s/2000s, with glacier melt in warm years being insufficient to offset lack of precipitation. On mid-sized glaciers at relatively low elevations and with limited vertical extent, in warmer years, the transient snow line was above the highest point of the glacier. Only on large glaciers descending from high elevations can rising transient snowlines continue to expose more ice to melt. Runoff from such large glaciers was enhanced in warm summers but reduction of overall ice area through glacier recession led to runoff in the warmest summer (2003) being lower than the previous peak discharge recorded in the second warmest year (1947).
Equilibrium speciation models were established for Hg (II), Cd (II) and Pb (II) in bog-, river- and sea water having a composition corresponding to that of the Gulf of Bothnia (6 ‰ salinity). The calculations were performed using the computer program SOLGASWATER. The models were based on available thermodynamic data at 25°C and included the inorganic ligands OH−, Cl−, Br−, HPO42− and CO2 (aq). Furthermore, complex formation with organic substances originating from a bog water was considered, Mg (II) and Ca (II) were also included as competing cations. All water types were assumed to be oxic and in equilibrium with atmospheric carbon dioxide, 10−3.5 atm (32 Pa).
The calculations showed that the speciation of Hg (II) and Pb (II) in bog and river waters is dominated by complexation with the organic substance, except for lead (II), where the Pb2+ -ion dominates at pH⩽5. In the Gulf of Bothnia, the chloro complexes HgCl2 and HgCl3− becomes prevailing as the salinity increases. Besides Pb2+, the species PbCl+ and PbCO3 become important upon increasing the salinity and pH. The dominating fraction of Cd (II) is Cd2+ in bog water, in river water and in waters of salinity lower than 4.5 ‰.
With increasing salinity CdCl+ and CdCl2predominate.
Seasonal variations in the stable isotopic composition of snow and meltwater were investigated in a sub-arctic, mountainous, but non-glacial, catchment at Okstindan in northern Norway based on analyses of delta(18)O and deltaD. Samples were collected during four field periods (August 1998; April 1999; June 1999 and August 1999) at three sites lying on an altitudinal transect (740-970 m a.s.l.). Snowpack data display an increase in the mean values of delta(18)O (increasing from a mean value of - 13.51 to - 11.49% between April and August), as well as a decrease in variability through the melt period. Comparison with a regional meteoric water line indicates that the slope of the delta(18)O - deltaD line for the snowpacks decreases over the same period, dropping from 7.49 to approximately 6.2. This change points to the role of evaporation in snowpack ablation and is confirmed by the vertical profile of deuterium excess. Snowpack seepage data, although limited, also suggest reduced values of deltaD, as might be associated with local evaporation during meltwater generation. In general, meltwaters were depleted in delta(18)O relative to the source snowpack at the peak of the melt (June), but later in the year (August) the difference between the two was not statistically significant. The diurnal pattern of isotopic composition indicates that the most depleted meltwaters coincide with the peak in temperature and, hence, meltwater production.
Wildfire is an important disturbance affecting hydrological processes through alteration of vegetation cover and soil characteristics. The effects of fire on hydrological systems at the catchment scale are not well known, largely because site specific data from both before and after wildfire are rare. In this study a modelling approach was employed for change detection analyses of one such dataset to quantify effects of wildfire on catchment hydrology. Data from the Entiat Experimental Forest (Washington State, US) were used, a conceptual runoff model was applied for pre- and post-fire periods and changes were analyzed in three different ways: reconstruction of runoff series, comparison of model parameters and comparison of simulations using parameter sets calibrated to the two different periods. On average, observed post-fire peak flows were 120% higher than those modelled based on pre-fire conditions. For the post-fire period, parameter values for the snow routine indicated deeper snow packs and earlier and more rapid snowmelt. The net effect of the changes in all parameters was largely increased post-fire peak flows. Overall, the analyses show that change detection modelling provides a viable alternative to the paired-watershed approach for analyzing wildfire disturbance effects on runoff dynamics and supports discussions on changes in hydrological processes.
The flow upstream of a free overfall from smooth inverted semicircular channels is theoretically analysed to compute the end-depth ratio (EDR), applying an energy equation based on the Boussinesq assumption. This approach eliminates the need for an experimentally determined pressure coefficient. Experiments were conducted with horizontal channel conditions. The EDR related to the critical depth, which occurs upstream from the end section, is found to be around 0.695 for a critical depth-diameter ratio up to 0.40. A simple method is presented to estimate the discharge from a known end-depth. The theoretical model corresponds closely with the experimental data.
A water quality model is used to assess the impact of possible climate change on dissolved oxygen (DO) in the Thames. The Thames catchment is densely populated and, typically, many pressures are anthropogenic. However, that same population also relies on the river for potable water supply and as a disposal route for treated wastewater. Thus, future water quality will be highly dependent on future activity. Dynamic and stochastic modelling has been used to assess the likely impacts on DO dynamics along the river system and the probability distributions associated with future variability. The modelling predictions indicate that warmer river temperatures and drought act to reduce dissolved oxygen concentrations in lowland river systems
A modelling study has been undertaken to assess the likely impacts of climate change on water quality across the UK. A range of climate change scenarios have been used to generate future precipitation, evaporation and temperature time series at a range of catchments across the UK. These time series have then been used to drive the Integrated Catchment (INCA) suite of flow, water quality and ecological models to simulate flow, nitrate, ammonia, total and soluble reactive phosphorus, sediments, macrophytes and epiphytes in the Rivers Tamar, Lugg, Tame, Kennet, Tweed and Lambourn. A wide range of responses have been obtained with impacts varying depending on river character, catchment location, flow regime, type of scenario and the time into the future. Essentially upland reaches of river will respond differently to lowland reaches of river, and the responses will vary depending on the water quality parameter of interest.
The cover is designed with a 0.5 m layer of clay covered by a 1.5 m layer of glacial till. Evaluation of cover effectiveness is based on: 1) the reduction of leachate production, and 2) the ability of the clay layer to remain water saturated and avoid cracking. The numerical model SUTRA simulates unsaturated flow in the cover, with results interpreted in terms of pressure head variations and vertical discharge from the cover. Results indicate that this cover design would adequately reduce leachate production from a tailing deposit. Water saturation of the clay layer remains above its plastic limit during a simulated year and therefore it is not likely to crack. A sensitivity analysis shows that leachate production is most sensitive to clay hydraulic conductivity, while the water saturation of the clay layer is sensitive to both clay hydraulic conductivity and till porosity. -from Author
Estimation of flood frequency based on instantaneous peak flow (IPF) is
important for the design of hydraulic structures. However, observed flow
data with high temporal resolution are scarce, especially regarding the
limited length of the available flow time series. Here, three different
methods are developed and compared to estimate the IPF based on maximum
daily flow (MDF), which is available usually at more gauges and for
longer time periods. In the first approach, simple linear regressions
with non-intercept of probability weighted moments (PWM) or quantile
values between IPF and MDF data are employed. Secondly, stepwise
multiple linear regressions is used to generate regression equations
describing the relationship between easily obtained catchment attributes
and MDF predictors and the IPF as target variable. With the third
method, the temporal scaling properties of IPF series based on the
hypothesis of piece wise simple scaling are investigated for 3 different
flow gauges with 15 min data and then utilized to estimate the IPF for
all gauges in the area. The study region is the Aller-Leine river basin
in northern Germany with 45 stream flow gauges. Cross validation results
from the three presented models show good performance in reproducing the
peak flow and the potential to be used in other catchment. The simple
regressions are the easiest to apply given enough peak flow data, the
scaling method is the most efficient one among these three models but
stepwise multiple linear regressions gives the best results compared
with the other two methods.
The application of Jenkinson's method to extremal distributions for low probability annual extremes of rainfall and stream flow is studied and discussed.
A statistical method devised by Jenkinson has been examined and compared with other methods of fitting extreme value distributions to observed data. The Jenkinson method, being strictly objective, has the particular advantage of taking into account the extreme part of the extreme value distribution. The author shows, by applying the Jenkinson method to extreme values which significantly belong to several different kinds of frequency distributions, that this method could be applied as a standard one. Finally, the author indicates the possibility of using the Jenkinson method to extrapolate statistical characteristics from a series of statistically unstable short-term data.
The Leaf Area Index (LAI) was derived from the Normalised Difference Vegetation Index (NDVI) obtained from Advanced Very High Resolution Radiometer (AVHRR) data for the years 1982-2004. The NDVI-derived LAI showed a very good agreement (correlation coefficient r up to 0.96) with MODIS LAI. To address the relation between precipitation and LAI, linear correlation analysis between gridded precipitation and the NDVI-derived LAI was conducted for several land uses and each month of the year. Based on the regression coefficients, LAI could be simulated as a function of precipitation. During validation, the simulated LAI showed a very good agreement (r >= 0.75) with the NDVI-derived LAI. The simulated dynamic LAI was thereafter implemented in a hydrological model. For comparison, a model run with a static LAI without any inter-annual variations was also conducted. During abnormally dry conditions, the dynamic LAI was lower than the static LAI and less transpiration was therefore simulated. It is shown that a dynamic LAI contributes to a more realistic simulation approach during individual weather events but also that in the long run the simulated transpiration is much more strongly influenced by inter-annual variations in weather than by the additional vegetation dynamics in a semi-arid region.
In order to study the possibility of reproducing river runoff with making use of the land surface model Soil Water–Atmosphere–Plants (SWAP) and information based on global data sets 11 river basins suggested within the framework of the Inter-Sectoral Impact Model Intercomparison Project and located in various regions of the globe under a wide variety of natural conditions were used. Schematization of each basin as a set of 0.5W × 0.5W computational grid cells connected by a river network was carried out. Input data including atmospheric forcing data and land surface parameters based, respectively, on the global WATCH and ECOCLIMAP data sets were prepared for each grid cell. Simulations of river runoff performed by SWAP with a priori input data showed poor agreement with observations. Optimization of a number of model parameters substantially improved the results. The obtained results confirm the universal character of SWAP. Natural uncertainty of river runoff caused by weather noise was estimated and analysed. It can be treated as the lowest limit of predictability of river runoff. It was shown that differences in runoff uncertainties obtained for different rivers depend greatly on natural conditions of a river basin, in particular, on the ratio of deterministic and random components of the river runoff.
Seasonal variations in chemistry and 13C/12C ratios of total inorganic carbon of carbonate dissolving waters are considered in the frame-work of a simplified approach dealing explicitly with major ionic species. The unidirectional evolution models of Deines et al. (1974) are supplemented by taking mixing effects into consideration (Wigley and Plummer 1976). These effects, caused mainly by the redistribution of carbon-bearing species in the mixture, are to a great extent nonlinear and unsymmetric with respect to the fraction of the second solution in a binary mixture. The theoretical considerations are supported by observations of many samples taken during a period from January to May 1977 in SW Lublin Upland.
The parameters PCO2 and δ13C of a reservoir lose their primary meaning in the case of mixing of waters but investigation of their changes may help in studying some conditions in the soil. During the period of observation (except March) the estimated values of PCO2 of a reservoir tended to he in a narrow range of values from 10−1.3 to 10−1.4 atm. In March those values were higher due to the large inflow of CO2-rich waters into the aquifer. The estimated δ13C values of a reservoir CO2 spread from –17 to –27 permil during January to March. In April and May those values focused in a narrow range from –22 to –26 permil. This tendency indicates that waters inflowing in March and April transported isotopically lighter CO2.
Both HCO3− content and δ13C of total carbon versus pH allowed to search inflows of infiltrating water into particular areas of the aquifer. It has been shown that δ13C investigations are necessary to notice the admixing of waters in certain cases.
The estimation of return periods for floods likely to have significant societal impact is challenging unless suitably long records exist. Relatively few sites across the UK provide a continuous record of river level or discharge over 50 years, whilst records extending back to the nineteenth century are rare. This represents a significant problem in providing robust and reliable estimates of flood risk, as relatively short records often fail to include an adequate sample of large floods. The inclusion of historical flood levels/magnitudes prior to instrumental river flow recording presents a valuable opportunity to extend this dataset. This paper examines the value of using historical data (both documentary and epigraphic) to augment existing gauged records for the River Trent in Central England, as part of a multi-method approach to assessing flood risk. Single station and pooled methods are compared with flood risk estimates based on an augmented historical series (1795-2008) using the generalised logistic and generalised Pareto distributions. The value of using an even longer, but less reliable, extended historical series (1320-2008) is also examined. It is recommended that modelling flood risk for return periods >100 years should incorporate historical data, where available, and that a multi-method approach increases confidence in flood risk estimates.
Soil water plays a crucial role in biogeochemical processes within karst ecosystems. However, geochemical variations of soil waters under different land covers and the related karst critical zone processes are still unclear. In this study, five land covers, including grassland, dry land, shrub land, reforestation land, and bamboo land in the Qingmuguan karst area of Chongqing Municipality, Southwest (SW) China were investigated in order to better understand the spatio-temporal variations of soil water geochemistry and its controlling mechanisms. The hydrochemistry of soil water and stable carbon isotopic compositions of dissolved inorganic carbon (δ13CDIC) in soil water were analyzed by a semi-monthly sampling strategy. The results show that there is remarkable spatio-temporal variation in the hydrochemistry and δ13CDIC of soil waters under different land covers in the studied area. Soil waters collected from shrub, dry, and afforestation lands have higher total dissolved solids (TDS), Ca2+, and HCO3− concentrations and heavier δ13CDIC, which is probably associated with the stronger carbonate dissolution caused by higher soil CO2 and carbonate content in soils under these land covers. However, lower TDS, Ca2+, and HCO3− concentrations as well as δ13CDIC values but higher SO42− concentrations are found in soil waters collected from bamboo land and grassland. The reason is that higher gypsum dissolution or oxidation of sulfide minerals and less soil CO2 input occurs in soils under these two land covers. Under the shrub, dry, and afforestation lands, higher concentrations of Ca2+ and HCO3− in soil waters occur in rainy seasons than in dry seasons, which are probably linked to higher CO2 input due to stronger microbial activities and root respiration in the wet summer seasons. In addition, seasonal variations of NO3− concentrations in soil waters from the dry land are observed, and much higher NO3− concentration occurs in the rainy seasons than that in the dry seasons, which suggest that the agricultural fertilization may lead to high NO3− in soil water. On the vertical soil profile, except for the bamboo land, soil waters under different land covers commonly show an increasing trend of main ion concentrations with the increase of depth. This vertical variation of hydrochemistry and δ13CDIC values in soil waters is primarily controlled by the intensity of carbonate dissolution related to carbonate content in soils and soil CO2 production. The soil waters under different land covers have great variations in δ13CDIC values which ranged from −20.68‰ to −6.90‰. Also, the [HCO3−]/([Ca2+] + [Mg2+]), [NO3−]/[HCO3−], and [SO42−]/([Ca2+] + [Mg2+]) molar ratios in soil waters show a large amplitude of variation. This suggested that carbonic acids could not be a unique dissolving agent and sulfuric/nitric acids may play a role in the weathering of carbonate in the Qingmuguan karst area.
Towards the end of November 2009, west Cumbria in northwest England experienced severe flooding which caused extensive damage and disruption throughout the region. The flooding was triggered by an exceptional rainstorm during which a record 316.4 mm of rainfall was recorded at Seathwaite Farm, Borrowdale over the 24-hour period up to 00: 00 on 20th November. Drawing on the results of a recent project which has developed a new model of point rainfall depth-duration-frequency (DDF) for the UK, return periods are estimated for the highest point rainfall observations available for the Cumbrian event and compared with frequency estimates derived from the Flood Estimation Handbook rainfall model (Faulkner 1999). The spatial and temporal characteristics of the storm event are examined using data from the Environment Agency's raingauge network. For the two most affected rivers, the Derwent and the Leven, return periods of catchment rainfall are estimated for durations up to 96 hours.
In order to use the best suited snow models to investigate snow conditions at ungauged sites and for a changed climate, we have tested four snow models for 17 catchments in Norway. The Crocus and seNorge models are gridded whereas the Distance Distribution Dynamics (DDD) model with its two versions, DDD_CX and DDD_EB, is catchment based. Crocus and DDD_EB use energy balance for estimating snowmelt and SeNorge and DDD_CX use temperature-index methods. SeNorge has calibrated the temperature-index against observed snowmelt, whereas DDD_CX has calibrated the temperature-index against runoff. The models use gridded temperature and precipitation at 1 h resolution for the period 2013–2016. Crocus needs additional forcing from a numerical weather prediction model, whereas DDD_EB calculates the energy-balance elements by using proxy models forced by temperature and precipitation. The threshold temperature for solid and liquid precipitation is common for all the models and equal to 0.5 C. No corrections of precipitation or temperature are allowed. The snow simulations are validated against observed snow water equivalent (SWE) and against satellite derived snow covered area (SCA). SeNorge and DDD_EB perform best with respect to both SWE and SCA suggesting model structures suited for describing snow conditions at ungauged sites and for a changed climate.
The application of hydrological models to data on conservative tracers can yield information about transit times and storage volumes and may provide an independent test of the model structure.
In this study, the PULSE-model has been modified to simulate conservative tracers. Attempts have been made to describe both short-term and long-term variations in oxygen-18 concentration in three small forested basins.
The performance of the model was considerably increased, when additional storage was introduced in the model. The turnover times were estimated to approximately 7 and 12 months for two of the basins.
Amount and oxygen-18 content of rainfall and throughfall have been monitored in a pine forest in Uppsala during summer 1983. It is found that the free throughfall coefficient, C, the canopy reservoir capacity, S, and the critical value of rain, R//0, are 0. 5, 2. 1 mm and 4. 1 mm respectively. The average value of throughfall is about 60% of rainfall. Generally, the thoughfall is enriched in oxygen-18 with respect to rainfall, but in very few cases depletion has been observed. The enrichment or depletion in throughfall have been graphically predicted and agree fairly well with the observations. Oxygen-18 values of throughfall have been simulated by a model describing isotopic fractionation in throughfall. Additional study results are discussed.
One hundred samples were collected from the surface of the Upper Fremont Glacier at equally spaced intervals defined by an 8,100 m2 snow grid to assess the significance of lateral variability in major-ion concentrations and del oxygen-18 values. For the major ions, the largest concentration range within the snow grid was sodium (0.5056 mg/l) and the smallest concentration range was sulfate (0.125 mg/l). Del oxygen-18 values showed a range of 7.45 per mil. Comparison of the observed variability of each chemical constituent to the variability expected by measurement error indicated substantial lateral variability within the surface-snow layer. Results of the nested ANOVA indicate most of the variance for every constituent is in the values grouped at the two smaller geographic scales (between 506 m2 and within 506 m2 sections). Calcium and sodium concentrations and del oxygen-18 values displayed the largest amount of variance at the largest geographic scale (between 2,025 m2 sections) within the grid and ranged from 14 to 26 per cent of the total variance. The variance data from the snow grid were used to develop equations to evaluate the significance of both positive and negative concentration/value peaks of nitrate and del oxygen-18 with depth, in a 160 m ice core. Solving the equations indicates that both the nitrate and del oxygen-18 ice-core profiles have concentration/value trends that exceed the limits expected from lateral variability. Values of del oxygen-18 in the section from 110-150 m below the surface consistently vary outside the expected limits and possibly represents cooler temperatures during the Little Ice Age from about 1810 to 1725 A.D.
Commencement of the Gravity Recovery and Climate Experiment (GRACE) provides an alternative way to monitor changes in terrestrial water storage (TWS) at large scales. However, GRACE dataset spans from 2002 to present, which greatly limits the application of GRACE data for long-term hydrological studies. Thus, the general linear model (GLM), random forest (RF), support vector machines (SVM), and artificial neural networks (ANN) methods were used to reconstruct the time series of terrestrial water storage anomalies (TWSA, i.e., remove the average value from the time series) in Northwest China (NWC) during 1948–2002 based on the GRACE TWSA during 2003–2015 and hydrological data from the Global Land Data Assimilation System (GLDAS) during 1948–2010. The results showed that soil moisture (SM) anomalies, or the combination of SM, canopy water (CW), and snow water equivalent (SWE) anomalies were better than the other anomalies of GLDAS in NWC. RF method can be regarded as the optimal method to reconstruct TWSA in NWC in the four models. A negative relationship was found between the reconstructed TWSAs and El Niño-Southern Oscillation (ENSO). The method could also offer an approach to reconstruct TWSA and drought events in large river basins during the past several decades.
This study evaluates the hydrometric monitoring maintained within the Canadian pan-Arctic and is based on the hydrometric gauges closest to northern seas for 76 river systems throughout 1950-2008. Monitoring is quantified by compiling time series of total gauged area and discharge values from the available hydrometric records. We further evaluate the quality of hydrometric data by examining the availability of hydrometric records, the continuity of individual records, and the influence of water regulation on river systems. The maximum gauged area of the Canadian pan-Arctic was 64% in 1990 before it slowly decreased to 56% in 2008. Larger river systems typically had the most hydrometric data available, though each river system had an average of 46% of their records available. In 1998, a maximum of 22 river systems had more than 30 years of continuous records, which is the maximum attained throughout the study period. For future improvements in hydrometric monitoring, additional gauges on relatively small rivers will need to be deployed. We suggest new gauges should be implemented in the Eastern Hudson Bay, Ungava Bay and Labrador Sea basins in spite of the tremendous need for more in the Arctic Archipelago.
A large portion of the freshwater in western Canada originates as snowpack from the northern Rocky Mountains. Temperature and precipitation in the region control the amount of snow accumulated and stored throughout the winter, and the intensity and timing of melt during the spring freshet. Therefore, trends in temperature, precipitation, snow accumulation, and snowmelt over western Canada are examined using the Mann-Kendall non-parametric test and an original GIS-based approach to trend analysis on a newly produced high-resolution gridded climate dataset for the period 1950–2010. Temporal and spatial analyses of these hydroclimatic variables reveal that daily minimum temperature has increased more than daily maximum temperature, particularly during the cold season, and at higher elevations, contributing to earlier spring melt. Precipitation has decreased throughout the cold season and increased in the warm season, particularly in the northern half of the study area. Snow accumulation has decreased through all months of the year while snowmelt results indicate slight increases in mid-winter melt events and an earlier onset of the spring freshet. This study provides a summary of detected trends in key hydroclimatic variables across western Canada regarding the effects these changes can have on the spring freshet and streamflow throughout the region.
This study aims to determine trends in annual and seasonal rainfall and rainy days over different river basins across India. The data used consists of daily gridded rainfall at 1° x 1 ° resolution for the period 1951-2004. Sen's non-parametric estimator of slope was used to estimate the magnitude of trend whose statistical significance was assessed by the Mann-Kendall test. Among 22 basins studied, 15 showed a decreasing trend in annual rainfall; only one basin showed a significant decreasing trend at 95% confidence level. Of the 6 basins showing an increasing trend, 1 basin showed a significant positive trend. The monsoon rainfall increased over 6 basins, decreased over 16 basins and a decreasing trend for 2 basins was found statistical significant. With the exception of Ganga, Brahmaputra and EFR4, all river basins experienced the same direction of trend in monsoon and annual rainfall. Four river basins experienced increasing (non-significant) trend in annual rainy days; three basins did not show any change in annual rainy days whereas 15 basins have shown a decreasing trend in annual rainy days. The decreasing trend in three basins was statistically significant. Most of the basins have shown the same direction of trend in rainfall and rainy days at the annual and seasonal scale.
Continuous changes in the global climate have exacerbated the uneven spatial distribution of water resources. The quantitative response relationships between precipitation and its influencing factors are an important research topic. In this study, the responses of precipitation to its influencing factors were quantified by analysing the large-spatial-scale data such as the monthly precipitation data of 619 meteorological stations in China from 1951 to 2018, the CMIP6 data, and the AMO through empirical orthogonal function decomposition, partial redundancy analysis, and ensemble empirical mode decomposition. As shown by the results, the overall response relationships between precipitation in China and the AMO and MEI were relatively strong, and the PDO and AGG affected precipitation in western China. The precipitation in the area north of 25 °N had strong response relationships with the SR and AO. AP affected the precipitation in Northeast China, while WS affected the precipitation in North China and western China. RH affected the precipitation in the regions south of 25 °N. The response relationship between precipitation and CO2 was weakest. The total contribution rate of the influencing factors to the annual precipitation was higher in the west and lower in the east. In the regions west of 100 °E, the total contribution rate of the influencing factors to annual precipitation increased from south to north. In the regions east of 100 °E, the total contribution rate of the influencing factors to the annual precipitation decreased from north and south to the central area, AO and AP contributed little to the annual precipitation across China. HIGHLIGHTS
Qualitative analysis of the relationship between precipitation and climate factors.;
Quantitative analysis of climate factors on precipitation.;
The inflow of river water to the Baltic Sea is evaluated for the period 1951–60. A proposal is made for a re-evaluation of the estimates for earlier periods and for future computations on a continuous basis.
The mid-1960s to early 1970s were a formative stage in hydrology in the UK. This was a period of a major increase in government funding for science. Establishing hydrology as an environmental science to compete for a share in this boost in funding with well-recognised subjects such as geology, ecology and oceanography depended on the work of enthusiastic scientists influencing the Natural Environment Research Council (NERC). Progress was made by key individuals not only by their own research contributions but also by their influential work within the government, exemplified by the roles of five physicists. In attempting to accelerate hydrological science, mistakes were made but, in this period, a major research institute was founded, large field catchment experiments were set up and research and training within UK universities increased significantly. The research is based on participant observation and examination of contemporary committee papers held in the UK National Archives, Kew and in the Science Museum Archive, Wroughton. HIGHLIGHTS
The social history of scientific hydrology in its formative years in the UK reveals complex relations between scientists and government.;
Five physicists played leading roles.;
An expensive laboratory catchment study failed.;
Hydrological science was defended against demand for precipitate applicability.;
Extreme precipitation events vary with different sub-regions, sites and years and show complex characteristics. In this study, the temporal variations, trends with significance and change points in the annual time series of 10 extreme precipitation indices (EPIs) at 552 sites and in seven sub-regions were analyzed using the modified Mann–Kendall test and sequential Mann–Kendall analysis. Three representative (extremely wet, normal and extremely dry) years from 1961 to 2017 were selected by the largest, 50%, and smallest empirical frequency values in China. The spatiotemporal changes in the EPIs during the three representative years were analyzed in detail. The results showed that during 1961–2017, both the consecutive wet or dry days decreased significantly, while the number of heavy precipitation days had no significant trend, and the other seven wet EPIs increased insignificantly. The abrupt change years of the 10 EPIs occurred 32 and 40 times from 1963 to 1978 and from 1990 to 2016, respectively, regardless of sub-region. The extremely dry (or wet) events mainly occurred in western (or southwestern) China, implying a higher extreme event risk. The extremely wet, normal and extremely dry events from 1961 to 2017 occurred in 2016, 1997 and 2011 with empirical frequencies of 1.7%, 50% and 98.3%, respectively. In addition, 1998 was the second-most extremely wet year (empirical frequency was 3.7%). The monthly precipitation values were larger from February to August in 1998, forming a much earlier flood peak than that of 2016. The 10 EPIs had close connections with Normalized Difference Vegetation Indexes during the 12 months of 1998 and 2016. This study provides useful references for disaster prevention in China.
Monthly climatic data from 53 sites across Xinjiang, China, were used to compare drought severity from the widely accepted Standardized Precipitation Index (SPI) with the recently proposed Standardized Precipitation Evapotranspiration Index (SPEI), as well as trends in the data from 1961 to 2013. Monthly Thornthwaite based (ETo.TW) and Penman-Monteith based reference evapotranspiration (ETo.PM) were computed and subsequently used to estimate SPEITW and SPEIPM, respectively. The indices' sensitivity, spatiotemporal distributions and trends were analyzed. The results showed that the TW equation underestimated ETo, which affected the accuracy of the SPEI estimation. Greater consistency was found between SPI and SPEIPM than between SPI and SPEITW at different timescales. SPI and SPEIPM were sensitive to precipitation, but SPEITW and SPEIPM were insensitive to ETo. The scope of spatial SPEIPM was wider than that of SPI at the same timescale. Obvious differences in SPI, SPEITW and SPEIPM existed between northern and southern Xinjiang. SPEIPM was a better indicator of global warming than SPI. Both SPI and SPEIPM had increasing trends, which contradict previously reported trends in global drought. In conclusion, the decrease in drought severity observed over the last 53 years may indicate some relief in the water utilization crisis in Xinjiang, China.
The Xinjiang province of China is vulnerable to drought, but the occurrence of drought varies substantially among different sub-areas. This study investigated drought characteristics in Xinjiang province and its sub-area using the Mann–Kendall trend test, cluster analysis and Morlet wavelet analysis. The results show that drought in Xinjiang is generally becoming less severe, and there is a non-uniform spatial variation of drought, which is especially pronounced for stations in northern Xinjiang. There is a unique spatiotemporal distribution trend of drought in Xinjiang, and the inter-decadal variation of drought shows a gradual shift from the east to the west and then back to the east again over the past 55 years. Northern Xinjiang is becoming wetter at a faster rate compared with that of southern Xinjiang, and it also has a higher occurrence of change point sites (70%). The historical drought situation in Xinjiang is better characterized by three clusters. Cluster 1 is the driest, cluster 2 has a clear alleviating tendency of drought, while cluster 3 shows late occurrence of change point. A broader view of the accumulated variation of drought is formulated in this study, which may help to identify potential droughts to support drought disaster management and mitigation.
Daily snow data during 1961–2013 at the 105 meteorological stations in Xinjiang, China were used to investigate the spatiotemporal variations of several parameters, including starting and ending dates, duration, annual and monthly average and maximum snow depths. The modified Mann–Kendall test, empirical mode decomposition, empirical orthogonal function (EOF), and the inverse distance weight interpolation were applied. Snow lasted for 71 to 120 days. Snow depth decreased from north to south. Daily snow depth had periodical variations and were classified as four typical types, i.e., flat peak, multi-peak, sharp single-peak, and right-skewed. After daily snow depth was decomposed into 17 intrinsic mode functions (IMFs), IMF9, IMF10, and IMF11 over 189, 302, and 437 days of scales accounted for 79% of the total spatiotemporal variance in snow depth. Both annual starting and ending day numbers had decreasing trends, while the duration in days had an increasing trend. The average and maximum snow depth increased in most sites whether considering the seasonality in December, January, February, or annual values. EOF1 accounted for 70% of spatial variability and the temporal coefficient EC1 varied periodically. The spatiotemporal analysis of snow properties provides a basis for snowmelt understanding.
This paper is based on the 2012 Penman Lecture delivered at the 11th National Symposium of the British Hydrological Society. The title is taken from a 1965 interview by Howard Penman when hydrological modelling was just really starting. In the period since then, the idea that we might easily move towards 'physically based' representations of hydrological processes has proven problematic. It is argued that this might best be done within a hypotheses testing framework, where the hypotheses are the model representations of processes over some discrete elements of a catchment, integrating the small-scale variability within those elements. This might still require some distribution function to reflect that variability, since the extremes of the variability might be important in controlling the response. Hypotheses will need to be formulated that reflect the interaction of the water flow pathways and the biota. Testing of those hypotheses will require a proper account of the uncertainties inherent in the study of hydrological systems, including a recognition that many sources of uncertainty are epistemic in nature rather than simple random variability. Such uncertainties will only be significantly reduced by the development of new measurement techniques that provide useful information at the element scales of interest.
Many studies have highlighted breaks in mean values of temperature and precipitation time series since the 1970s. Given that temperatures have continued to increase following that decade, the first question addressed in this study is whether other breaks in mean values have occurred since that time. The second question is to determine which climate indices influence temperature and rainfall in the coastal region of Northern Algeria. To address these two questions, we analyzed the temporal variability of temperature and annual and seasonal rainfall as they relate to four climate indices at seven coastal stations in Algeria during the 1972–2013 period using the Mann–Kendall, Lombard, and canonical correlation (CC) analysis methods.The annual and seasonal maximum, minimum and mean temperatures increased significantly over that time period. Most of these increases are gradual, implying a slow warming trend. In contrast, total annual and seasonal rainfall did not show any significant change. CC analysis revealed that annual and seasonal temperatures are negatively correlated with the Western Mediterranean Oscillation (WeMOI Q3) climate index that characterizes atmospheric circulation over the Mediterranean basin. On the other hand, rainfall is positively correlated with a large-scale atmospheric index such as Southern Oscillation Index.
Changes in observed streamflow records for 131 catchments from the state of Victoria in southeast Australia are investigated for the 1975-2011 study period. Seven flood indices are considered which are derived from annual maximum, peak-over-threshold (POT) and monthly maximum flood series. Trend analyses are undertaken using Mann-Kendall (MK) and seasonal MK tests along with the bootstrap resampling approach to account for serial correlation. A common trend direction in all months in streamflow data for the majority of the stations has been identified by Van Belle and Hughes' homogeneity test. Trend analyses results show the percentages of stations exhibiting significant downward trends ranges from 4 to 35% at 5% significance level, which is generally higher than the percentage of stations to occur by chance. Good agreement is found between trends in the AM and POT flood magnitude time series, and separately in the POT flood frequency time series, but not between flood magnitude and their associated frequency series. More stations with significant negative trends have transpired in the AM than in the POT flood data series. Resemblance in the results between both the MK and seasonal MK tests for most of the catchments is also noticed.