Showing papers in "Hydrological Processes in 2009"
TL;DR: In this paper, the authors examined concentration-discharge relationships for solutes produced primarily by mineral weathering in 59 geochemically diverse US catchments and found that these catchments exhibit nearly chemostatic behaviour; their stream concentrations of weathering products such as Ca, Mg, Na, and Si typically vary by factors of only 3 to 20 while discharge varies by several orders of magnitude.
Abstract: Concentration–discharge relationships have been widely used as clues to the hydrochemical processes that control runoff chemistry. Here we examine concentration–discharge relationships for solutes produced primarily by mineral weathering in 59 geochemically diverse US catchments. We show that these catchments exhibit nearly chemostatic behaviour; their stream concentrations of weathering products such as Ca, Mg, Na, and Si typically vary by factors of only 3 to 20 while discharge varies by several orders of magnitude. Similar patterns are observed at the inter-annual time scale. This behaviour implies that solute concentrations in stream water are not determined by simple dilution of a fixed solute flux by a variable flux of water, and that rates of solute production and/or mobilization must be nearly proportional to water fluxes, both on storm and inter-annual timescales. We compared these catchments' concentration–discharge relationships to the predictions of several simple hydrological and geochemical models. Most of these models can be forced to approximately fit the observed concentration–discharge relationships, but often only by assuming unrealistic or internally inconsistent parameter values. We propose a new model that also fits the data and may be more robust. We suggest possible tests of the new model for future studies. The relative stability of concentration under widely varying discharge may help make aquatic environments habitable. It also implies that fluxes of weathering solutes in streams, and thus fluxes of alkalinity to the oceans, are determined primarily by water fluxes. Thus, hydrology may be a major driver of the ocean-alkalinity feedback regulating climate change. Copyright © 2009 John Wiley & Sons, Ltd.
620 citations
TL;DR: A review of recent studies investigating linkages between permafrost dynamics and river biogeochemistry in the Arctic is presented in this article, including consideration of likely impacts that warming-induced changes in permfrost may be having (or will have in the future) on the delivery of organic matter, inorganic nutrients, and major ions to the Arctic Ocean.
Abstract: Over the next century, near-surface permafrost across the circumpolar Arctic is expected to degrade significantly, particularly for land areas south of 70°N. This is likely to cause widespread impacts on arctic hydrology, ecology, and trace gas emissions. Here, we present a review of recent studies investigating linkages between permafrost dynamics and river biogeochemistry in the Arctic, including consideration of likely impacts that warming-induced changes in permafrost may be having (or will have in the future) on the delivery of organic matter, inorganic nutrients, and major ions to the Arctic Ocean. These interacting processes can be highly complex and undoubtedly exhibit spatial and temporal variabilities associated with current permafrost conditions, sensitivity to permafrost thaw, mode of permafrost degradation (overall permafrost thaw, active layer deepening, and/or thermokarst processes), and environmental characteristics of watersheds (e.g. land cover, soil type, and topography). One of the most profound consequences of permafrost thaw projected for the future is that the arctic terrestrial freshwater system is likely to experience a transition from a surface water-dominated system to a groundwater-dominated system. Along with many other cascading impacts from this transition, mineral-rich groundwater may become an important contributor to streamflow, in addition to the currently dominant contribution from mineral-poor surface water. Most studies observe or predict an increase in major ion, phosphate, and silicate export with this shift towards greater groundwater contributions. However, we see conflicting accounts of whether the delivery of inorganic nitrogen and organic matter will increase or decrease with warming and permafrost thaw. It is important to note that uncertainties in the predictions of the total flux of biogeochemical constituents are tightly linked to future uncertainties in discharge of rivers. Nonetheless, it is clear that over the next century there will be important shifts in the river transport of organic matter, inorganic nutrients, and major ions, which may in turn have critical implications for primary production and carbon cycling on arctic shelves and in the Arctic Ocean basin interior. Copyright © 2008 John Wiley & Sons, Ltd.
605 citations
TL;DR: In this paper, the authors examined whether mountain snowpack and snowmelt have manifested a consistent hydrologic response to global climatic changes over the past several decades and compared the spatial and temporal patterns of trends in the volume, extent, and seasonality of snowpack.
Abstract: Mountain snowpack and spring runoff are key components of surface water resources, and serve as important, regionally integrated indicators of climate variability and change. This study examines whether mountain snowpack and snowmelt have manifested a consistent hydrologic response to global climatic changes over the past several decades. Prior findings are compared to identify spatial and temporal patterns of trends in the volume, extent, and seasonality of snowpack and melt for key mountain regions. Evidence suggests that both temperature and precipitation increases to date have impacted mountain snowpacks simultaneously on the global scale; however, the nature of the impact is, among other factors, strongly dependent on geographic location, latitude, and elevation. Warmer temperatures at mid-elevations have decreased snowpack and resulted in earlier melt in spite of precipitation increases, while they have not affected high-elevation regions that remain well below freezing during winter. At high elevations, precipitation increases have resulted in increased snowpack. Not all local responses are consistent with the general findings, possibly because of local climatic trends, atmospheric circulation patterns, record lengths, or data quality issues. With continued warming, increasingly higher elevations are projected to experience declines in snowpack accumulation and melt that can no longer be offset by winter precipitation increases. There is a continued research need for hydroclimatic trend detection and attribution in mountains owing to the length, quality, and sparseness of available data from monitoring stations not directly impacted by human activity. Copyright © 2008 John Wiley & Sons, Ltd.
447 citations
TL;DR: In this paper, a physically-based hydrologic model was used to assess the effects of systematic changes in precipitation and temperature on snow-affected portions of the global land area as projected by a suite of global climate models.
Abstract: For most of the global land area poleward of about 40° latitude, snow plays an important role in the water cycle. The (seasonal) timing of runoff in these areas is especially sensitive to projected losses of snowpack associated with warming trends, whereas projected (annual) runoff volume changes are primarily associated with precipitation changes, and to a lesser extent, with changes in evapotranspiration (ET). Regional studies in the USA (and especially the western USA) suggest that hydrologic adjustments to a warming climate have been ongoing since the mid-twentieth century. We extend the insights extracted from the western USA to the global scale using a physically based hydrologic model to assess the effects of systematic changes in precipitation and temperature on snow-affected portions of the global land area as projected by a suite of global climate models. While annual (and in some cases seasonal) changes in precipitation are a key driver of projected changes in annual runoff, we find, as in the western USA, that projected warming produces strong decreases in winter snow accumulation and spring snowmelt over much of the affected area regardless of precipitation change. Decreased snowpack produces decreases in warm-season runoff in many mid- to high-latitude areas where precipitation changes are either moderately positive or negative in the future projections. Exceptions, however, occur in some high-latitude areas, particular in Eurasia, where changes in projected precipitation are large enough to result in increased, rather than decreased, snow accumulation. Overall, projected changes in snowpack and the timing of snowmelt-derived runoff are largest near the boundaries of the areas that currently experience substantial snowfall, and at least qualitatively, they mirror the character of observed changes in the western USA. Copyright © 2008 John Wiley & Sons, Ltd.
432 citations
TL;DR: In this paper, a reexamination of more than 60 years of water and sediment-discharge data indicates that dams alone are not the sole cause of sediment discharges in the Missouri-Mississippi River system.
Abstract: Before 1900, the Missouri–Mississippi River system transported an estimated 400 million metric tons per year of sediment from the interior of the United States to coastal Louisiana. During the last two decades (1987–2006), this transport has averaged 145 million metric tons per year. The cause for this substantial decrease in sediment has been attributed to the trapping characteristics of dams constructed on the muddy part of the Missouri River during the 1950s. However, reexamination of more than 60 years of water- and sediment-discharge data indicates that the dams alone are not the sole cause. These dams trap about 100–150 million metric tons per year, which represent about half the decrease in sediment discharge near the mouth of the Mississippi. Changes in relations between water discharge and suspended-sediment concentration suggest that the Missouri–Mississippi has been transformed from a transport-limited to a supply-limited system. Thus, other engineering activities such as meander cutoffs, river-training structures, and bank revetments as well as soil erosion controls have trapped sediment, eliminated sediment sources, or protected sediment that was once available for transport episodically throughout the year. Removing major engineering structures such as dams probably would not restore sediment discharges to pre-1900 state, mainly because of the numerous smaller engineering structures and other soil-retention works throughout the Missouri–Mississippi system. Published in 2009 by John Wiley & Sons, Ltd.
353 citations
TL;DR: The glaciers of western Canada and the conterminous United States have dominantly retreated since the end of the Little Ice Age (LIA) in the nineteenth century, although average rates of retreat varied from strong in the first-half of the twentieth century, with glaciers stabilizing or even advancing until 1980, and then resuming consistent recession as mentioned in this paper.
Abstract: The glaciers of western Canada and the conterminous United States have dominantly retreated since the end of the Little Ice Age (LIA) in the nineteenth century, although average rates of retreat varied from strong in the first-half of the twentieth century, with glaciers stabilizing or even advancing until 1980, and then resuming consistent recession. This retreat has been accompanied by statistically detectable declines in late-summer streamflow from glacier-fed catchments over much of the study area, although there is some geographical variation: over recent decades, glaciers in northwest BC and southwest Yukon have lost mass dominantly by thinning with relatively low rates of terminal retreat, and glacier-fed streams in that region have experienced increasing flows. In many valleys, glacier retreat has produced geomorphic hazards, including outburst floods from moraine-dammed lakes, mass failures from oversteepened valley walls and debris flows generated on moraines. In addition to these hydrologic and geomorphic changes, evidence is presented that glacier retreat will result in higher stream temperatures, possibly transient increases in suspended sediment fluxes and concentrations, and changes in water chemistry. With climate projected to continue warming over the twenty-first century, current trends in hydrology, geomorphology and water quality should continue, with a range of implications for water resources availability and management and hydroecology, particularly for cool and cold-water species such as salmonids. Copyright © 2008 John Wiley & Sons, Ltd.
298 citations
TL;DR: In this article, the authors used SWAT and SUFI-2 to calibrate and validate a hydrologic model of Iran based on river discharges and wheat yield, taking into consideration dam operations and irrigation practices.
Abstract: Knowledge of the internal renewable water resources of a country is strategic information which is needed for long-term planning of a nation's water and food security, among many other needs. New modelling tools allow this quantification with high spatial and temporal resolution. In this study we used the program Soil and Water Assessment Tool (SWAT) in combination with the Sequential Uncertainty Fitting program (SUFI-2) to calibrate and validate a hydrologic model of Iran based on river discharges and wheat yield, taking into consideration dam operations and irrigation practices. Uncertainty analyses were also performed to assess the model performance. The results were quite satisfactory for most of the rivers across the country. We quantified all components of the water balance including blue water flow (water yield plus deep aquifer recharge), green water flow (actual and potential evapotranspiration) and green water storage (soil moisture) at sub-basin level with monthly time-steps. The spatially aggregated water resources and simulated yield compared well with the existing data. The study period was 1990–2002 for calibration and 1980–1989 for validation. The results show that irrigation practices have a significant impact on the water balances of the provinces with irrigated agriculture. Concerning the staple food crop in the country, 55% of irrigated wheat and 57% of rain-fed wheat are produced every year in water-scarce regions. The vulnerable situation of water resources availability has serious implications for the country's food security, and the looming impact of climate change could only worsen the situation. This study provides a strong basis for further studies concerning the water and food security and the water resources management strategies in the country and a unified approach for the analysis of blue and green water in other arid and semi-arid countries. Copyright © 2008 John Wiley & Sons, Ltd.
284 citations
TL;DR: In this paper, a general increase in the richness and production of micro-organisms, algae, macroinvertebrates and fish as glacier hydrological influence shrinks under a warmer climate was predicted.
Abstract: Aquatic ecosystems in high latitude and altitude environments are strongly influenced by cryospheric and hydrological processes due to links between atmospheric forcing, snowpack/glacier mass-balance, river discharge, physico-chemistry and biota In the current phase of global climate warming, many glaciers are shrinking Loss of snow and ice-masses will alter spatial and temporal dynamics in bulk basin runoff with important changes in the relative contributions of snowmelt, glaciermelt and groundwater to stream flow Accordingly, altered water source contributions will be accompanied by changes to fluvial, solute, sediment and thermal regimes and, thus, channel stability and habitat The projected reduction in sediment load, warmer water temperature and increased channel stability will drive significant shifts in the floral and faunal composition of glacier-fed rivers This paper hypothesizes a general increase in the richness and production of micro-organisms, algae, macroinvertebrates and fish as glacier hydrological influence shrinks under a warmer climate With reduced glacial influence, macroinvertebrate species trait diversity will increase with more organisms possessing larger body size, less specialized body shape and lower adult mobility In larger river systems, potential reduction of meltwater inputs will have a significant influence on off-channel habitats (eg side-channels and sloughs) that depend on glacial runoff to sustain habitat availability and connectivity, particularly for fish Some species such as cold stenothermic taxa (including some endemic macroinvertebrates) may be vulnerable to extinction and therefore gamma (regional) diversity will be reduced These sensitive macroinvertebrate taxa may be important biological indicators of environmental change in glacierized river basins Moreover, high climatic sensitivity and low human perturbation make glacially influenced river basins early indicator systems for identifying hydrological and ecological responses to climate change/variability It is concluded that glacier shrinkage and associated changes in runoff amount and timing, water source contributions and physico-chemical habitat will be a major driver of the future biodiversity of stream communities in cold environments Research imperatives and future directions are proposed for investigation of glacier-fed river hydroecology Copyright © 2008 John Wiley & Sons, Ltd
277 citations
TL;DR: In this paper, the authors argue that impact studies often tend to be overly optimistic about the reliability of their predictions, and overly pessimistic about the effects on society, and contrast this assessment with our views on the current state of change prediction, and outline the opportunities in this exciting field of hydrologic research.
Abstract: Although Einstein was referring to quantum mechanics in this statement rather than to hydrology, one sometimes does wonder whether we are throwing the dice in hydrological analyses. When two experts estimate the 100-year flood in a small ungauged catchment, chances are that their estimates are very different. When two groups predict the effects of future hydrological changes on stream flow and recharge for the same catchment, the results will hardly be consistent. Yet, climate change impact analyses have become a standard method in our tool box for addressing issues that seem to be of overwhelming concern to the society today. In this paper, we argue that impact studies often tend to be overly optimistic about the reliability of their predictions, and overly pessimistic about the effects on society. Just as a medical doctor who, when in doubt, would say that his patient is going to die—to be on the safe side. We will contrast this assessment with our views on the current state of change prediction, and outline the opportunities in this exciting field of hydrologic research.
277 citations
TL;DR: The Lake Tana Basin is of significant importance to Ethiopia concerning water resources aspects and the ecological balance of the area as discussed by the authors. But many years of mismanagement, wetland losses due to urban encroach...
Abstract: Lake Tana Basin is of significant importance to Ethiopia concerning water resources aspects and the ecological balance of the area. Many years of mismanagement, wetland losses due to urban encroach ...
245 citations
TL;DR: Despite an increasing number of empirical investigations of catchment transit times (TTs), virtually all are based on individual catchments and there are few attempts to synthesize understanding ac... as discussed by the authors.
Abstract: Despite an increasing number of empirical investigations of catchment transit times (TTs), virtually all are based on individual catchments and there are few attempts to synthesize understanding ac ...
TL;DR: Troch et al. as mentioned in this paper proposed SAHRA (Sustainability of semi-arid hydrology and riparian areas), which is a semiarid water management model.
Abstract: Peter A. Troch1,2* Guillermo F. Martinez1 Valentijn R. N. Pauwels3 Matej Durcik4 Murugesu Sivapalan5,6 Ciaran Harman6 Paul D. Brooks1,4 Hoshin Gupta1,4 and Travis Huxman7,2 1 Department of Hydrology and Water Resources, University of Arizona, USA 2 Biosphere 2 Earthscience, University of Arizona, USA 3 Laboratory of Hydrology and Water Management, Ghent University, Belgium 4 SAHRA (Sustainability of semi-arid hydrology and riparian areas), University of Arizona, USA 5 Department of Geography, University of Illinois at Urbana-Champaign, USA 6 Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, USA 7 Department of Ecology and Evolutionary Biology, University of Arizona, USA
TL;DR: In this paper, a combination of climate change and land cover change scenarios for 2040 with the semi-distributed AVSWAT hydrological model was used to determine changes in mean runoff depths in the 2040s (2030-2059) from the baseline period (1973-2002) at the monthly, seasonal, and annual scales.
Abstract: Climate changes brought on by increasing greenhouse gases in the atmosphere are expected to have a significant effect on the Pacific Northwest hydrology during the 21st century. Many climate model simulations project higher mean annual temperatures and temporal redistribution of precipitation. This is of particular concern for highly urbanized basins where runoff changes are more vulnerable to changes in climate. The Rock Creek basin, located in the Portland metropolitan area, has been experiencing rapid urban growth throughout the last 30 years, making it an ideal study area for assessing the effect of climate and land cover changes on runoff. A combination of climate change and land cover change scenarios for 2040 with the semi-distributed AVSWAT (ArcView Soil and Water Assessment Tool) hydrological model was used to determine changes in mean runoff depths in the 2040s (2030–2059) from the baseline period (1973–2002) at the monthly, seasonal, and annual scales. Statistically downscaled climate change simulation results from the ECHAM5 general circulation model (GCM) found that the region would experience an increase of 1·2 °C in the average annual temperature and a 2% increase in average annual precipitation from the baseline period. AVSWAT simulation shows a 2·7% increase in mean annual runoff but a 1·6% decrease in summer runoff. Projected climate change plus low-density, sprawled urban development for 2040 produced the greatest change to mean annual runoff depth (+5·5%), while climate change plus higher-density urban development for 2040 resulted in the smallest change (+5·2%), when compared with the climate and land cover of the baseline period. This has significant implications for water resource managers attempting to implement adaptive water resource policies to future changes resulting from climate and urbanization. Copyright © 2008 John Wiley & Sons, Ltd.
TL;DR: In this paper, the authors present an assessment of future snow and runoff in two Alpine catchments, the larger Inn catchment (1945 km2) and the smaller Dischma catchments (43 km2), based on two common climate change scenario (IPCC A2 and B2), and predict changes in snow cover and discharge using Alpine3D, a model for the high-resolution simulation of Alpine surface processes.
Abstract: The snow cover in the Alps is heavily affected by climate change. Recent data show that at altitudes below 1200 m a.s.l. a time-continuous winter snow cover is becoming an exception rather than the rule. This would also change the timing and characteristics of river discharge in Alpine catchments. We present an assessment of future snow and runoff in two Alpine catchments, the larger Inn catchment (1945 km2) and the smaller Dischma catchment (43 km2), based on two common climate change scenario (IPCC A2 and B2 (IPCC, 2007)). [etc]. The changes in snow cover and discharge are predicted using Alpine3D, a model for the high-resolution simulation of Alpine surface processes, in particular snow, soil and vegetation processes. The predicted changes in snow and discharge are extreme. While the current climate still supports permanent snow and ice on the highest peaks at altitudes above 3000 m a.s.l., this zone would disappear under the future climate scenarios. The changes in snow cover could be summarized by approximately shifting the elevation zones down by 900 m. The corresponding changes in discharge are also severe: while the current climate scenario shows a significant contribution from snow melt until middle to late summer, the future climate scenarios would feature a much narrower snow melt discharge peak in spring. A further observation is that heavy precipitation events in the fall would change from mainly snow to mainly rain and would have a higher probability of producing flooding. Future work is needed to quantify the effect of model uncertainties on such predictions. Copyright © 2008 John Wiley & Sons, Ltd.
TL;DR: In this paper, the main objective of the study was to identify the most vulnerable areas to soil erosion in the Lake Tana Basin, Blue Nile, Ethiopia using the Soil and Water Assessment Tool (SWAT).
Abstract: The main objective of this study was to identify the most vulnerable areas to soil erosion in the Lake Tana Basin, Blue Nile, Ethiopia using the Soil and Water Assessment Tool (SWAT), a physically ...
TL;DR: In this paper, the impact of land cover and climate change on hydrological processes was investigated using the SWAT tool and the results showed that surface water is more sensitive to land cover change and climate changes.
Abstract: Land-cover/climate changes and their impacts on hydrological processes are of widespread concern and a great challenge to researchers and policy makers. Kejie Watershed in the Salween River Basin in Yunnan, South-West China, has been reforested extensively during the past two decades. In terms of climate change, there has been a marked increase ill temperature. The impact of these changes oil hydrological processes required investigation: hence, this paper assesses aspects of changes in land cover and climate. The response of hydrological processes to land-cover/climate changes was examined using the Soil and Water Assessment Tool (SWAT) and impacts of single factor, land-use/climate change on hydrological processes were differentiated. Land-cover maps revealed extensive reforestation at the expense of grassland, cropland, and barren land. A significant monotonic trend and noticeable changes had Occurred in annual temperature over the long term. Long-term changes in annual rainfall and streamflow were weak; and changes in monthly rainfall (May, June, July, and September) were apparent. Hydrological simulations showed that the impact of climate change oil Surface water, baseflow, and streamflow was offset by the impact of land-cover change. Seasonal variation in streamflow was influenced by seasonal variation in rainfall. The earlier onset of monsoon and the variability of rainfall resulted in extreme monthly streamflow. Land-cover change played a dominant role in mean annual Values; seasonal variation in surface water and streamflow was influenced mainly by seasonal variation in rainfall; and land-cover change played a regulating role in this. Surface water is more sensitive to land-cover change and climate change: an increase in surface water in September and May due to increased rainfall was offset by a decrease in surface water due to land-cover change. A decrease in baseflow caused by changes in rainfall and temperature was offset by all increase in baseflow due to land-cover change. Copyright (C) 2009 John Wiley & Sons, Lid.
TL;DR: In this paper, the link of river ice to the hydrology of northern rivers is examined in detail and the rise in river stage that is caused by an ice cover is shown to be fundamental to ice-related hydrologic impacts, such as floods caused by freezeup and breakup ice jams, low winter flows caused by water storage during freezeup, and sharp waves generated by ice-jam releases.
Abstract: Many rivers of cold, and even temperate, regions of the globe are covered with ice for a part of the year. Projections of future climate indicate that the duration, composition and extent of ice coverage, however, will gradually change. This may have wide-ranging consequences because ice is a critical component of cold-regions hydrologic systems and strongly affects, for example, extreme floods, low winter flows, river transport, hydroelectric production, and numerous ecological and water-quality characteristics. Following an overview of the processes characterizing the freezeup-ice growth-breakup sequence, the links of river ice to the hydrology of northern rivers are examined in detail. The rise in river stage that is caused by an ice cover is shown to be fundamental to ice-related hydrologic impacts, such as floods caused by freezeup and breakup ice jams, low winter flows caused by water storage during freezeup and sharp waves generated by ice-jam releases. Ice thickness and strength, both controlled by weather conditions, also play major roles. To date, the sensitivity of river-ice regimes to changes in climatic conditions has only been partly evaluated. Most studies have focussed on ice phenology and indicate trends that are consistent with changes in air temperature, while a few recent studies have addressed the more complex questions of how climate change may alter ice thickness or the severity of extreme ice jams and floods. Foreseeable changes to river-ice regimes, and associated hydrologic processes and impacts, are discussed in the light of current understanding. More frequent occurrence of mid-winter breakup and associated jamming is a major effect that can be predicted with some confidence for regions where such events are presently rare or unknown. It is stressed that gaps in current knowledge preclude quantitative prediction of site-specific changes to river-ice regimes, and several recommendations for future research are presented. Copyright © 2008 Her Majesty the Queen in right of Canada. Published by John Wiley & Sons, Ltd.
TL;DR: In this article, the concurrent effects of changing climate (primarily temperature) and land cover in the basin are deconvolved, based on land cover maps for 1883 and 2002, and gridded climate data for 1915-2006.
Abstract: The Puget Sound basin in northwestern Washington, USA has experienced substantial land cover and climate change over the last century. Using a spatially distributed hydrology model (the Distributed Hydrology-Soil-Vegetation Model, DHSVM) the concurrent effects of changing climate (primarily temperature) and land cover in the basin are deconvolved, based on land cover maps for 1883 and 2002, and gridded climate data for 1915–2006. It is found that land cover and temperature change effects on streamflow have occurred differently at high and low elevations. In the lowlands, land cover has occurred primarily as conversion of forest to urban or partially urban land use, and here the land cover signal dominates temperature change. In the uplands, both land cover and temperature change have played important roles. Temperature change is especially important at intermediate elevations (so-called transient snow zone), where the winter snow line is most sensitive to temperature change—notwithstanding the effects of forest harvest over the same part of the basin. Model simulations show that current land cover results in higher fall, winter and early spring streamflow but lower summer flow; higher annual maximum flow and higher annual mean streamflow compared with pre-development conditions, which is largely consistent with a trend analysis of model residuals. Land cover change effects in urban and partially urban basins have resulted in changes in annual flow, annual maximum flows, fall and summer flows. For the upland portion of the basin, shifts in the seasonal distribution of streamflows (higher spring flow and lower summer flow) are clearly related to rising temperatures, but annual streamflow has not changed much. Copyright 2009 John Wiley & Sons, Ltd.
TL;DR: In this article, measurements were conducted in coniferous forests of differing density, insolation and latitude to test whether air temperatures are suitable surrogates for canopy temperature in estimating sub-canopy longwave irradiance to snow.
Abstract: Measurements were conducted in coniferous forests of differing density, insolation and latitude to test whether air temperatures are suitable surrogates for canopy temperature in estimating sub-canopy longwave irradiance to snow. Air temperature generally was a good representation of canopy radiative temperature under conditions of low insolation. However during high insolation, needle and branch temperatures were well estimated by air temperature only in relatively dense canopies and exceeded air temperatures elsewhere. Tree trunks exceeded air temperatures in all canopies during high insolation, with the relatively hottest trunks associated with direct interception of sunlight, sparse canopy cover and dead trees. The exitance of longwave radiation from these relatively warm canopies exceeded that calculated assuming canopy temperature was equal to air temperature. This enhancement was strongly related to the extinction of shortwave radiation by the canopy. Estimates of sub-canopy longwave irradiance using either two-energy source or two thermal regime approaches to evaluate the contribution of canopy longwave exitance performed better than did estimates that used only air temperature and sky view. However, there was little evidence that such corrections are necessary under cloudy or low solar insolation conditions. The longwave enhancement effect due to shortwave extinction was important to sub-canopy longwave irradiance to snow during clear, sunlit conditions. Longwave enhancement increased with increasing solar elevation angle and decreasing air temperature. Its relative importance to longwave irradiance to snow was insensitive to canopy density. As errors from ignoring enhanced longwave contributions from the canopy accumulate over the winter season, it is important for snow energy balance computations to include the enhancement in order to better calculate snow internal energy and therefore the timing and magnitude of snowmelt and sublimation. Copyright © 2009 John Wiley & Sons, Ltd.
TL;DR: In this paper, the authors compared the performance of the two most widely used watershed-scale models, the Annualized AGricultural Non-Point Source (AnnAGNPS) and Soil and Water Assessment Tool (SWAT), in the Cheney Lake watershed in southcentral Kansas.
Abstract: This study was conducted under the USDA-Conservation Effects Assessment Project (CEAP) in the Cheney Lake watershed in south-central Kansas. The Cheney Lake watershed has been identified as ‘impaired waters’ under Section 303(d) of the Federal Clean Water Act for sediments and total phosphorus. The USDA-CEAP seeks to quantify environmental benefits of conservation programmes on water quality by monitoring and modelling. Two of the most widely used USDA watershed-scale models are Annualized AGricultural Non-Point Source (AnnAGNPS) and Soil and Water Assessment Tool (SWAT). The objectives of this study were to compare hydrology, sediment, and total phosphorus simulation results from AnnAGNPS and SWAT in separate calibration and validation watersheds. Models were calibrated in Red Rock Creek watershed and validated in Goose Creek watershed, both sub-watersheds of the Cheney Lake watershed. Forty-five months (January 1997 to September 2000) of monthly measured flow and water quality data were used to evaluate the two models. Both models generally provided from fair to very good correlation and model efficiency for simulating surface runoff and sediment yield during calibration and validation (correlation coefficient; R2, from 0·50 to 0·89, Nash Sutcliffe efficiency index, E, from 0·47 to 0·73, root mean square error, RMSE, from 0·25 to 0·45 m3 s−1 for flow, from 158 to 312 Mg for sediment yield). Total phosphorus predictions from calibration and validation of SWAT indicated good correlation and model efficiency (R2 from 0·60 to 0·70, E from 0·63 to 0·68) while total phosphorus predictions from validation of AnnAGNPS were from unsatisfactory to very good (R2 from 0·60 to 0·77, E from − 2·38 to 0·32). The root mean square error–observations standard deviation ratio (RSR) was estimated as excellent (from 0·08 to 0·25) for the all model simulated parameters during the calibration and validation study. The percentage bias (PBIAS) of the model simulated parameters varied from unsatisfactory to excellent (from 128 to 3). This study determined SWAT to be the most appropriate model for this watershed based on calibration and validation results. Copyright © 2008 John Wiley & Sons, Ltd.
TL;DR: In this paper, large-scale atmospheric variables were downscaled to meteorological variables at local scale for the daily time step to assess hydrological impacts by climate changes. But the results of the downscaling revealed that precipitation does not manifest a systematic increase or decrease in all future time horizons for both A2 and B2 scenarios.
Abstract: In this study, large-scale atmospheric variables are downscaled to meteorological variables at local scale for the daily time step to assess hydrological impacts by climate changes. Large-scale atmospheric modelling was by the HadCM3 General Circulation Model (GCM) while downscaling and water balance modelling was through the Statistical DownScaling Model and the HBV semi-distributed rainfall-runoff model, respectively. The area of study was the Gilgel Abay catchment that drains in Lake Tana. A selection of large-scale atmospheric variables by the HadCM3 GCM are downscaled by a multiple linear regression model, were minimum and maximum temperature and precipitation for future time horizons are calculated. Climate scenarios as developed for the A2 (medium-high emission) and B2 (medium-low emission) scenarios for a 100-year period based on the mean of 20 ensembles have been selected for this study. In addition, a synthetic incremental scenario was tested for a wide range of changes in climatic variables. Stream flow simulations by the HBV model were carried out for the 2020s (2011―2040), 2050s (2041-2070) and 2080s (2071-2099) to define hydrologic impacts. The result of downscaled precipitation reveals that precipitation does not manifest a systematic increase or decrease in all future time horizons for both A2 and B2 scenarios unlike that of minimum and maximum temperature and related evaporation. For the future horizons significant changes and variations in the seasonal and monthly flows are to be expected and for the 2080s the runoff volume in the rainy season will reduce by approximately 11·6 and 10·1% for the A2 and B2 scenarios. Results from synthetic incremental scenarios also indicate sensitivities to climate change. As much as 33% of the seasonal and annual runoff is expected to reduce when temperature increases by 2°C and when rainfall decreases by approximately 20%.
TL;DR: In this paper, water-table elevation, temperature, and specific conductivity along a transect perpendicular to the Colorado River (Austin, Texas, USA), 15 km downstream of the Longhorn dam were monitored.
Abstract: Dam operations commonly cause large, frequent fluctuations in river stage, which persist for long distances downstream. The stage fluctuations force river water into and out of the banks, defining lateral hyporheic exchange paths. To evaluate the penetration distance and rates of dam-induced hyporheic exchange, we monitored water-table elevation, temperature, and specific conductivity along a transect perpendicular to the Colorado River (Austin, Texas, USA), 15 km downstream of the Longhorn dam. Stage fluctuates daily by almost a metre. The daily hyporheic exchange volume per metre of bank is 1·0 m 3 . Dam-induced hyporheic exchange penetrates several metres into the riparian aquifer, while water-table fluctuations propagate 30 m into the riparian aquifer. Water chemistry and temperature fluctuate near the channel in response to the flow oscillations. In the absence of dam operations, groundwater would flow steadily through the riparian aquifer towards the river, laterally limiting hyporheic exchange and stabilizing temperatures and water chemistry near the channel. Therefore, dam operations fundamentally change the hydrological, thermal, and geochemical dynamics of riparian aquifers and their hyporheic zones.
TL;DR: In this paper, a logistic regression model and Iverson's physically-based model were used to estimate the probability of landslide failure in a 180 km2 area in northern Italy.
Abstract: Probabilistic thresholds for triggering shallow landslides by rainfall are developed using two approaches: a logistic regression model and Iverson's physically based model. Both approaches are applied to a 180 km2 area in northern Italy. For the physically based model a Monte Carlo approach is used to obtain probabilities of slope failure associated with differing combinations of rainfall intensity and duration as well as differing topographic settings. For the logistic regression model hourly and daily rainfall data and split-sample testing are used to explore the effect of antecedent rainfall on triggering thresholds. It is demonstrated that both the statistical and physically based models provide stochastic thresholds that express the probability of landslide triggering. The resulting thresholds are comparable, even though the two approaches are conceptually different. The physically based model also provides an estimate of the percentage of potentially unstable areas in which failure can be triggered with a certain probability. The return period of rainfall responsible for landslide triggering is studied by using a Gumbel scaling model of rainfall intensity–duration–frequency curves. It is demonstrated that antecedent rainfall must be taken into account in landslide forecasting, and a method is proposed to correct the rainfall return period by filtering the rainfall maxima with a fixed threshold of antecedent rainfall. This correction produces an increase of the return periods, especially for rainstorms of short duration. Copyright © 2009 John Wiley & Sons, Ltd.
TL;DR: In this paper, the authors identify simple connections between observations of hydrological processes at the hillslope scale and observations of the response of watersheds following rainfall, with a view to building a parsimonious model of catchment processes.
Abstract: The purpose of this paper is to identify simple connections between observations of hydrological processes at the hillslope scale and observations of the response of watersheds following rainfall, with a view to building a parsimonious model of catchment processes. The focus is on the well-studied Panola Mountain Research Watershed (PMRW), Georgia, USA. Recession analysis of discharge Q shows that while the relationship between dQ/dt and Q is approximately consistent with a linear reservoir for the hillslope, there is a deviation from linearity that becomes progressively larger with increasing spatial scale. To account for these scale differences conceptual models of streamflow recession are defined at both the hillslope scale and the watershed scale, and an assessment made as to whether models at the hillslope scale can be aggregated to be consistent with models at the watershed scale.
Results from this study show that a model with parallel linear reservoirs provides the most plausible explanation (of those tested) for both the linear hillslope response to rainfall and non-linear recession behaviour observed at the watershed outlet. In this model each linear reservoir is associated with a landscape type. The parallel reservoir model is consistent with both geochemical analyses of hydrological flow paths and water balance estimates of bedrock recharge. Overall, this study demonstrates that standard approaches of using recession analysis to identify the functional form of storage–discharge relationships identify model structures that are inconsistent with field evidence, and that recession analysis at multiple spatial scales can provide useful insights into catchment behaviour. Copyright © 2008 John Wiley & Sons, Ltd.
TL;DR: The results show that genetic algorithms (GA) outperform the other four algorithms given model evaluation numbers larger than 2000, while particle swarm optimization (PSO) can obtain better parameter solutions than other algorithms given fewer number of model runs.
Abstract: With the popularity of complex hydrologic models, the time taken to run these models is increasing substantially. Comparing and evaluating the efficacy of different optimization algorithms for calibrating computationally intensive hydrologic models is becoming a nontrivial issue. In this study, five global optimization algorithms (genetic algorithms, shuffled complex evolution, particle swarm optimization, differential evolution, and artificial immune system) were tested for automatic parameter calibration of a complex hydrologic model, Soil and Water Assessment Tool (SWAT), in four watersheds. The results show that genetic algorithms (GA) outperform the other four algorithms given model evaluation numbers larger than 2000, while particle swarm optimization (PSO) can obtain better parameter solutions than other algorithms given fewer number of model runs (less than 2000). Given limited computational time, the PSO algorithm is preferred, while GA should be chosen given plenty of computational resources. When applying GA and PSO for parameter optimization of SWAT, small population size should be chosen. Copyright © 2008 John Wiley & Sons, Ltd.
TL;DR: In this article, the authors developed simple hydrology and erosion models using saturation excess runoff principles and interflow processes appropriate for a monsoonal climate and a mountainous landscape, which was applied to the Blue Nile.
Abstract: Models accurately representing the underlying hydrological processes and sediment dynamics in the Nile Basin are necessary for optimum use of water resources. Previous research in the Abay (Blue Nile) has indicated that direct runoff is generated either from saturated areas at the lower portions of the hillslopes or from areas of exposed bedrock. Thus, models that are based on infiltration excess processes are not appropriate. Furthermore, many of these same models are developed for temperate climates and might not be suitable for monsoonal climates with distinct dry periods in the Nile Basin. The objective of this study is to develop simple hydrology and erosion models using saturation excess runoff principles and interflow processes appropriate for a monsoonal climate and a mountainous landscape. We developed a hydrology model using a water balance approach by dividing the landscape into variable saturated areas, exposed rock and hillslopes. Water balance models have been shown to simulate river flows well at intervals of 5 days or longer when the main runoff mechanism is saturation excess. The hydrology model was developed and coupled with an erosion model using available precipitation and potential evaporation data and a minimum of calibration parameters. This model was applied to the Blue Nile. The model predicts direct runoff from saturated areas and impermeable areas (such as bedrock outcrops) and subsurface flow from the remainder of the hillslopes. The ratio of direct runoff to total flow is used to predict the sediment concentration by assuming that only the direct runoff is responsible for the sediment load in the stream. There is reasonable agreement between the model predictions and the 10-day observed discharge and sediment concentration at the gauging station on Blue Nile upstream of Rosaries Dam at the Ethiopia-Sudan border.
TL;DR: In this paper, a simple analytical solution for 1D vertical heat transport to temperature data observed at particular well-selected times of the year can provide an inexpensive, simple method to obtain accurate point estimates of groundwater-surface water exchange in rivers and lakes.
Abstract: Heat is recognized as a natural tracer to identify the exchange of water between the groundwater and surface water compartment. One-dimensional (1D) heat transport models have the ability to obtain quantitative estimates of vertical fluxes through the sediment matrix. Input to these models can come from temperatures observed in the surface water and in the bed material of rivers and lakes. The upper thermal boundary condition at the groundwater-surface water interface is affected by seasonal and diurnal temperature variations. We hypothesize that effects of these transient influences are negligible at certain times of the year, such that the vertical temperature distribution can be approximated to be at steady state. Temperature time series observed over a year in the surface water and at several depths below a river in Belgium and in sediments of an acid mine lake in Eastern Germany were simulated with a heat balance model implemented in FEMME and the water and energy model VS2DH to obtain seepage fluxes. Temperature variations throughout the year at all depths could be adequately reproduced with the transient models. Vertical temperature profiles at several measuring times during the year were also fitted with an analytical, steady-state solution for 1D heat transport and the obtained fluxes compared to the results from transient simulations. Fluxes obtained from the much simpler steady-state solution were compared well with the flux rates from transient simulations for moments between mid and late summer, as well as during the winter. During transitional seasons (fall and spring), the fluxes from the steady-state solution deviated significantly from the transient estimates with a tendency to underestimate at the beginning and to overestimate towards the end of those seasons. We conclude that fitting a simple analytical solution for 1D vertical heat transport to temperature data observed at particular well-selected times of the year can provide an inexpensive, simple method to obtain accurate point estimates of groundwater―surface water exchange in rivers and lakes.
TL;DR: For example, Marsh et al. as mentioned in this paper analyzed aerial photographs and topographic maps and found that 41 lakes were drained in the study area between 1950 and 2000, for a rate of slightly less than one lake per year.
Abstract: The permafrost of the Western Canadian Arctic has a very high ground ice content. As a result, the vast number of thaw lakes in this area are very sensitive to a changing climate. With thaw lakes prone to either increases in area due to thermokarst processes, or complete drainage in less than one day due to melting of channels through ice-rich permafrost. After a lake drains, it leaves a topographic basin that is often termed a Drained Thaw Lake Basin (DTLB). An analysis of aerial photographs and topographic maps showed that 41 lakes drained in the study area between 1950 and 2000, for a rate of slightly less than one lake per year. The rate of drainage over three time periods (1950–1973, 1973–1985, 1985–2000), decreased from over 1 lake/year to approximately 0·3 lake/year. The reason for this decrease is not known, but it is hypothesized that it is related to the effect of a warming climate. There is a large spatial variation in DTLBs, with higher number of drained lakes in physiographic areas with poor drainage. It is likely that this variation is related to variations in ground ice. Although previous studies have suggested that lakes drain during periods of high water level, it is likely that a combination of a warm summer, a resulting deep active layer, and a moderately high lake level were responsible for the drainage of a lake in the study area during the summer of 1989. Although this study has documented changes in the rate of lake drainage over a 50-year period, there is a need for further research to better understand the complex interactions between climate, geomorphology, and hydrology responsible for this change, and to further consider the potential hazard rapid lake drainage poses to future industrial or resource development in the area. Copyright © 2008 John Wiley & Sons, Ltd and Her Majesty the Queen in right of Canada. The contributions of P. Marsh, M. Russell, H. Haywood and C. Onclin belong to the Crown in right of Canada and are reproduced with the permission of Environment Canada.
TL;DR: In this paper, the authors assimilated water level information derived from a fused satellite Synthetic Aperture Radar (SAR) image and digital terrain model (DTM) with simulations from a coupled hydrological and hydrodynamic model to estimate discharge in an un-gauged basin scenario.
Abstract: River discharge is currently monitored by a diminishing network of gauges, which provide a spatially incomplete picture of global discharges. This study assimilated water level information derived from a fused satellite Synthetic Aperture Radar (SAR) image and digital terrain model (DTM) with simulations from a coupled hydrological and hydrodynamic model to estimate discharge in an un-gauged basin scenario. Assimilating water level measurements led to a 79% reduction in ensemble discharge uncertainty over the coupled hydrological hydrodynamic model alone. Measurement bias was evident, but the method still provided a means of improving estimates of discharge for high flows. The study demonstrates the potential of currently available synthetic aperture radar imagery to reduce discharge uncertainty in un-gauged basins when combined with model simulations in a data assimilation framework, where sufficient topographic data are available. The work is timely because in the near future the launch of satellite radar missions will lead to a significant increase in the volume of data available for space-borne discharge estimation. Copyright © 2009 John Wiley & Sons, Ltd.
TL;DR: In this paper, the authors present a model framework based on a land surface topography that can be represented with various degrees of resolution and capable of providing representative channel/floodplain hydraulic characteristics on a daily to hourly scale.
Abstract: Presented here is a model framework based on a land surface topography that can be represented with various degrees of resolution and capable of providing representative channel/floodplain hydraulic characteristics on a daily to hourly scale. The framework integrates two models: (1) a water balance model (WBM) for the vertical fluxes and stores of water in and through the canopy and soil layers based on the conservation of mass and energy, and (2) a routing model for the horizontal routing of surface and subsurface runoff and channel and floodplain waters based on kinematic and diffusion wave methodologies. The WBM is driven by satellite-derived precipitation (TRMM 3B42) and air temperature (MOD08 M3). The model’s use of an irregular computational grid is intended to facilitate parallel processing for applications to continental and global scales. Results are presented for the Amazon Basin over the period Jan 2001 through Dec 2005. The model is shown to capture annual runoff totals, annual peaks, seasonal patterns, and daily fluctuations over a range of spatial scales (>1, 000 to <4Ð7M km 2 ). For the period of study, results suggest basin-wide total water storage changes in the Amazon vary by approximately C/� 5 to 10 cm, and the fractional components accounting for these changes are: root zone soil moisture (20%), subsurface water being routed laterally to channels (40%) and channel/floodplain discharge (40%). Annual variability in monthly water storage changes by C/� 2Ð5 cm is likely due to 0Ð5 to 1 month variability in the arrival of significant rainfall periods throughout the basin. Copyright 2009 John Wiley & Sons, Ltd.