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Water Balance (water + balance)
Kinds of Water Balance Terms modified by Water Balance Selected AbstractsPan Evaporation Trends and the Terrestrial Water Balance.GEOGRAPHY COMPASS (ELECTRONIC), Issue 2 2009Pan evaporation is just that , it is the evaporation rate of water from a small dish located at the ground-surface. Pan evaporation is a measure of the evaporative demand over terrestrial surfaces. Declines in pan evaporation have now been reported in many regions of the world. The trends vary from one pan to the next, but when averaged over many pans, they are typically in the range of ,1 to ,4 mm a,2 (mm per annum per annum). In energetic terms, a trend of ,2 mm a,2 is equivalent to ,0.16 W m,2 a,1 and over 30 years this is a change of ,4.8 W m,2. For comparison, the top-of-atmosphere forcing due to doubled CO2 is estimated by the Intergovernmental Panel on Climate Change (IPCC) to be ~3.7 W m,2. Hence, the magnitude of the pan evaporation trend is large. What is of even greater interest is the direction , a decline , given the well-established warming of the last 30,50 years. In this article, the first in a two part series, we describe the underlying principles in using and interpreting pan evaporation data and then summarise the reported observations from different countries. In the second article, we describe the interpretation of the trends in terms of changes in the terrestrial water balance. [source] Pan Evaporation Trends and the Terrestrial Water Balance.GEOGRAPHY COMPASS (ELECTRONIC), Issue 2 2009Declines in pan evaporation have been reported across the USA, former Soviet Union, India, China, Australia, New Zealand and Canada, among other places. The trend is large , approximately an order of magnitude larger than model-based estimates of top of the atmosphere radiative forcing. The pan evaporation trend also has a different sign (i.e. decline) from commonly held conceptions. These are a remarkably interesting set of observations. In the first article of this two-part series, we discussed the measurements themselves and then presented summaries of the worldwide observations. In this, the second article, we outline the use of energy balance methods to attribute the observed changes in pan evaporation to changes in the underlying physical variables, namely, radiation, temperature, vapour pressure deficit and wind speed. We find that much of the decline in pan evaporation can be attributed to declines in radiation (i.e. dimming) and/or wind speed (i.e. stilling). We then discuss the interpretation of changes in the terrestrial water balance. This has been an area of much misunderstanding and confusion, most of which can be rectified through use of the familiar and longstanding supply/demand framework. The key in using the pan evaporation data to make inferences about changes in the terrestrial water balance is to distinguish between water- and energy-limited conditions where different interpretations apply. [source] The impact of groundwater,surface water interactions on the water balance of a mesoscale lowland river catchment in northeastern GermanyHYDROLOGICAL PROCESSES, Issue 2 2007Stefan Krause Abstract The glacially formed northeastern German lowlands are characterized by extensive floodplains, often interrupted by relatively steep moraine hills. The hydrological cycle of this area is governed by the tight interaction of surface water dynamics and the corresponding directly connected shallow groundwater aquifer. Runoff generation processes, as well as the extent and spatial distribution of the interaction between surface water and groundwater, are controlled by floodplain topography and by surface water dynamics. A modelling approach based on extensive experimental analyses is presented that describes the specific water balance of lowland areas, including the interactions of groundwater and surface water, as well as reflecting the important role of time-variable shallow groundwater stages for runoff generation in floodplains. In the first part, experimental investigations of floodplain hydrological characteristics lead to a qualitative understanding of the water balance processes and to the development of a conceptual model of the water balance and groundwater dynamics of the study area. Thereby model requirements which allow for an adequate simulation of the floodplain hydrology, considering also interactions between groundwater and surface water have been characterized. Based on these analyses, the Integrated Modelling of Water Balance and Nutrient Dynamics (IWAN) approach has been developed. This consists of coupling the surface runoff generation and soil water routines of the deterministic, spatially distributed hydrological model WASIM-ETH-I with the three-dimensional finite-difference-based numerical groundwater model MODFLOW and Processing MODFLOW. The model was applied successfully to a mesoscale subcatchment of the Havel River in northeast Germany. It was calibrated for two small catchments (1·4 and 25 km2), where the importance of the interaction processes between groundwater and surface waters and the sensitivity of several controlling parameters could be quantified. Validation results are satisfying for different years for the entire 198 km2 catchment. The model approach was further successfully tested for specific events. The experimental area is a typical example of a floodplain-dominated landscape. It was demonstrated that the lateral flow processes and the interactions between groundwater and surface water have a major importance for the water balance and periodically superimposed on the vertical runoff generation. Copyright © 2006 John Wiley & Sons, Ltd. [source] Comparison of stormflow responses of surface-mined and forested watersheds in the Appalachian Mountains, USAHYDROLOGICAL PROCESSES, Issue 16 2006Timothy L. Negley Abstract The results of a hydrological analysis that was conducted as part of a larger, multifaceted, collaborative effort to quantify ecosystem functions in watersheds subjected to land-use and land-cover change are presented. The primary goal of the study was to determine whether a small watershed in the Appalachian region (USA) that was recently subjected to surface mining and reclamation practices produces stormflow responses to rain events that are different from those produced by a nearby reference watershed covered by young, second-growth forest. Water balances indicated that runoff yields did not vary significantly between the two watersheds on an annual basis. Statistically significant differences (p,0·05) in runoff responses were observed on an event basis, however, with the mined/reclaimed watershed producing, on average (a) higher storm runoff coefficients (2·5×), (b) greater total storm runoff (3×), and (c) higher peak hourly runoff rates (2×) when compared with the reference watershed. Results of a unit hydrograph analysis also showed, unexpectedly, that the modelled unit responses of the two watersheds to effective rainfall pulses were similar, despite the noted differences in land cover. Differences in stormflow responses were thus largely explained by dramatic reductions in cumulative rates of rainfall abstraction (measured using infiltrometers) attributable to soil compaction during land reclamation. Additional field hydrological measurements on other mined watersheds will be needed to generalize our results, as well as to understand and predict the cumulative hydrological impacts of widespread surface mining in larger watersheds and river basins. Copyright © 2006 John Wiley & Sons, Ltd. [source] The brain angiotensin IV/AT4 receptor system as a new target for the treatment of Alzheimer's diseaseDRUG DEVELOPMENT RESEARCH, Issue 7 2009John W. Wright Abstract The brain renin-angiotensin system (RAS) regulates several physiologies including blood pressure, body sodium and water balance, cyclicity of reproductive hormones and related sexual behaviors, and the release of pituitary gland hormones. These physiologies are under the control of the angiotensin II (AngII)/AT1 receptor subtype system. The AngII/AT2 receptor subtype system is expressed during fetal development and is less abundant in the adult. This system appears to oppose growth responses facilitated by activation of the AT1 receptor. There is a growing list of nontraditional physiologies mediated by the most recently discovered angiotensin IV (AngIV)/AT4 receptor subtype system that include the regulation of blood flow, modulation of exploratory behaviors, involvement in stress responses and seizure, and a role in learning and memory acquisition. There is evidence to support an inhibitory influence by AngII, and a facilitory role by AngIV, on neuronal firing rate, long-term potentiation, and associative and spatial learning and memory. These findings suggest an important role for the RAS, and the AT4 receptor in particular, in normal cognitive processing and provide the stimulus for developing drugs that penetrate the blood-brain barrier to interact with this brain receptor in the treatment of dysfunctional memory. Drug Dev Res 70: 472,480, 2009. © 2009 Wiley-Liss, Inc. [source] Geographic body size gradients in tropical regions: water deficit and anuran body size in the Brazilian CerradoECOGRAPHY, Issue 4 2009Miguel Á. Olalla-Tárraga A recent interspecific study found Bergmann's size clines for Holarctic anurans and proposed an explanation based on heat balance to account for the pattern. However, this analysis was limited to cold temperate regions, and exploring the patterns in warmer tropical climates may reveal other factors that also influence anuran body size variation. We address this using a Cerrado anuran database. We examine the relationship between mean body size in a grid of 1° cells and environmental predictors and test the relative support for four hypotheses using an AIC-based model selection approach. Also, we considered three different amphibian phylogenies to partition the phylogenetic and specific components of the interspecific variation in body size using a method analogous to phylogenetic eigen vector regression (PVR). To consider the potential effects of spatial autocorrelation we use eigenvector-based spatial filters. We found the largest species inhabiting high water deficit areas in the northeast and the smallest in the wet southwest. Our results are consistent with the water availability hypothesis which, coupled with previous findings, suggests that the major determinant of interspecific body size variation in anurans switches from energy to water towards the equator. We propose that anuran body size gradients reflect effects of reduced surface to volume ratios in larger species to control both heat and water balance. [source] Comparison of soil moisture and meteorological controls on pine and spruce transpirationECOHYDROLOGY, Issue 3 2008Eric E. Small Abstract Transpiration is an important component of the water balance in the high elevation headwaters of semi-arid drainage basins. We compare the importance of soil moisture and meteorological controls on transpiration and quantify how these controls are different at a ponderosa pine site and a spruce site in the Jemez river drainage basin of northern New Mexico, a sub-basin of the Rio Grande. If only soil moisture controls fluctuations in transpiration, then simple hydrologic models focussed only on soil moisture limitations are reasonable for water balance studies. If meteorological controls are also critical, then more complex models are required. We measured volumetric water content in the soil and sap velocity, and assumed that transpiration is proportional to sap velocity. Ponderosa sap velocity varies with root zone soil moisture. Nearly all of the scatter in the ponderosa sap velocity,soil moisture relationship can be predicted using a simple model of potential evapotranspiration (ET), which depends only on measured incident radiation and air temperature. Therefore, simple hydrologic models of ponderosa pine transpiration are warranted. In contrast, spruce sap velocity does not clearly covary with soil moisture. Including variations in potential evapotranspiration does not clarify the relationship between sap velocity and soil moisture. Likewise, variations in radiation, air temperature, and vapour pressure do not explain the observed fluctuations in sap velocity, at least according to the standard models and parameters for meteorological restrictions on transpiration. Both the simple and more complex models commonly used to predict transpiration are not adequate to model the water balance in the spruce forest studied here. Copyright © 2008 John Wiley & Sons, Ltd. [source] Percolation characteristics of a water-repellent sandy forest soilEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2008G. Wessolek Summary In a tracer experiment TDR transect measurements were made to study percolation behaviour in a 120-year-old pine stand (Pinus sylvestris) on a water-repellent sandy soil (Haplic Arenosol). The experiment (with potassium iodide) showed an 80% labelling of the total flow in organic layers, whereas the area of transport in the mineral soil was sharply reduced to 12,30%. The average diameters of these preferential flow paths were about 8,15 cm. The TDR measurements indicate a homogeneous flow only for a short period from February until April. At this time of the year preferential flow is insignificant, because the soil is at approximately field capacity and not repellent to water. During summer (May to September) the soil dries out, and most precipitation results in preferential flow during this period. For any daily rainfall exceeding 10 mm, water infiltrates down to 1 m depth in the soil, which nevertheless, is still within the root zone. This kind of deep percolation results in the subsoil's wetting to field capacity (pF 1.8) earlier than the topsoil. A one-dimensional numerical model (SWAP) was used to simulate mean water balance with hydraulic functions with and without a water-repellency term. From the results of our tracer experiment we showed that the de-watering process in spring could be simulated well using the traditional piston flow concept, while the rewetting behaviour could be described more realistically using the mobile,immobile concept for water repellency. [source] Physiological and morphological responses of the soil bacterium Rhodococcus opacus strain PD630 to water stressFEMS MICROBIOLOGY ECOLOGY, Issue 2 2004Héctor M. Alvarez Abstract Rhodococcus opacus PD630 was investigated for physiological and morphological changes under water stress challenge. Gluconate- and hexadecane-grown cells were extremely resistant to these conditions, and survival accounted for up to 300 and 400 days; respectively, when they were subjected to slow air-drying. Results of this study suggest that strain PD630 has specific mechanisms to withstand water stress. Water-stressed cells were sensitive to the application of ethanol, high temperatures and oxidative stress, whereas they exhibited cross-protection solely against osmotic stress during the first hours of application. Results indicate that the resistance programme for water stress in R. opacus PD630 includes the following physiological and morphological changes, among others: (1) energetic adjustments with drastic reduction of the metabolic activity (,39% decrease during the first 24 h and about 90% after 190 days under dehydration), (2) endogenous metabolism using intracellular triacylglycerols for generating energy and precursors, (3) biosynthesis of different osmolytes such as trehalose, ectoine and hydroxyectoine, which may achieve a water balance through osmotic adjustment and may explain the overlap between water and osmotic stress, (4) adjustments of the cell-wall through the turnover of mycolic acid species, as preliminary experiments revealed no evident changes in the thickness of the cell envelope, (5) formation of short fragmenting-cells as probable resistance forms, (6) production of an extracellular slime covering the surface of colonies, which probably regulates internal and external c anges in water potential, and (7) formation of compact masses of cells. This contributes to understanding the water stress resistance processes in the soil bacterium R. opacus PD630. [source] Pan Evaporation Trends and the Terrestrial Water Balance.GEOGRAPHY COMPASS (ELECTRONIC), Issue 2 2009Pan evaporation is just that , it is the evaporation rate of water from a small dish located at the ground-surface. Pan evaporation is a measure of the evaporative demand over terrestrial surfaces. Declines in pan evaporation have now been reported in many regions of the world. The trends vary from one pan to the next, but when averaged over many pans, they are typically in the range of ,1 to ,4 mm a,2 (mm per annum per annum). In energetic terms, a trend of ,2 mm a,2 is equivalent to ,0.16 W m,2 a,1 and over 30 years this is a change of ,4.8 W m,2. For comparison, the top-of-atmosphere forcing due to doubled CO2 is estimated by the Intergovernmental Panel on Climate Change (IPCC) to be ~3.7 W m,2. Hence, the magnitude of the pan evaporation trend is large. What is of even greater interest is the direction , a decline , given the well-established warming of the last 30,50 years. In this article, the first in a two part series, we describe the underlying principles in using and interpreting pan evaporation data and then summarise the reported observations from different countries. In the second article, we describe the interpretation of the trends in terms of changes in the terrestrial water balance. [source] Pan Evaporation Trends and the Terrestrial Water Balance.GEOGRAPHY COMPASS (ELECTRONIC), Issue 2 2009Declines in pan evaporation have been reported across the USA, former Soviet Union, India, China, Australia, New Zealand and Canada, among other places. The trend is large , approximately an order of magnitude larger than model-based estimates of top of the atmosphere radiative forcing. The pan evaporation trend also has a different sign (i.e. decline) from commonly held conceptions. These are a remarkably interesting set of observations. In the first article of this two-part series, we discussed the measurements themselves and then presented summaries of the worldwide observations. In this, the second article, we outline the use of energy balance methods to attribute the observed changes in pan evaporation to changes in the underlying physical variables, namely, radiation, temperature, vapour pressure deficit and wind speed. We find that much of the decline in pan evaporation can be attributed to declines in radiation (i.e. dimming) and/or wind speed (i.e. stilling). We then discuss the interpretation of changes in the terrestrial water balance. This has been an area of much misunderstanding and confusion, most of which can be rectified through use of the familiar and longstanding supply/demand framework. The key in using the pan evaporation data to make inferences about changes in the terrestrial water balance is to distinguish between water- and energy-limited conditions where different interpretations apply. [source] Type and spatial structure of distribution data and the perceived determinants of geographical gradients in ecology: the species richness of African birdsGLOBAL ECOLOGY, Issue 5 2007Jana M. McPherson ABSTRACT Aim, Studies exploring the determinants of geographical gradients in the occurrence of species or their traits obtain data by: (1) overlaying species range maps; (2) mapping survey-based species counts; or (3) superimposing models of individual species' distributions. These data types have different spatial characteristics. We investigated whether these differences influence conclusions regarding postulated determinants of species richness patterns. Location, Our study examined terrestrial bird diversity patterns in 13 nations of southern and eastern Africa, spanning temperate to tropical climates. Methods, Four species richness maps were compiled based on range maps, field-derived bird atlas data, logistic and autologistic distribution models. Ordinary and spatial regression models served to examine how well each of five hypotheses predicted patterns in each map. These hypotheses propose productivity, temperature, the heat,water balance, habitat heterogeneity and climatic stability as the predominant determinants of species richness. Results, The four richness maps portrayed broadly similar geographical patterns but, due to the nature of underlying data types, exhibited marked differences in spatial autocorrelation structure. These differences in spatial structure emerged as important in determining which hypothesis appeared most capable of explaining each map's patterns. This was true even when regressions accounted for spurious effects of spatial autocorrelation. Each richness map, therefore, identified a different hypothesis as the most likely cause of broad-scale gradients in species diversity. Main conclusions, Because the ,true' spatial structure of species richness patterns remains elusive, firm conclusions regarding their underlying environmental drivers remain difficult. More broadly, our findings suggest that care should be taken to interpret putative determinants of large-scale ecological gradients in light of the type and spatial characteristics of the underlying data. Indeed, closer scrutiny of these underlying data , here the distributions of individual species , and their environmental associations may offer important insights into the ultimate causes of observed broad-scale patterns. [source] IHMS,Integrated Hydrological Modelling System.HYDROLOGICAL PROCESSES, Issue 19 2010Part 2. Abstract The integrated hydrological modelling system, IHMS, has been described in detail in Part 1 of this paper. The system comprises three models: Distributed Catchment Scale Model (DiCaSM), MODFLOW (v96 and v2000) and SWI. The DiCaSM simulates different components of the unsaturated zone water balance, including groundwater recharge. The recharge output from DiCaSM is used as input to the saturated zone model MODFLOW, which subsequently calculates groundwater flows and head distributions. The main objectives of this paper are: (1) to show the way more accurate predictions of groundwater levels in two Cyprus catchments can be obtained using improved estimates of groundwater recharge from the catchment water balance, and (2) to demonstrate the interface utility that simulates communication between unsaturated and saturated zone models and allows the transmission of data between the two models at the required spatial and temporal scales. The linked models can be used to predict the impact of future climate change on surface and groundwater resources and to estimate the future water supply shortfall in the island up to 2050. The DiCaSM unsaturated zone model was successfully calibrated and validated against stream flows with reasonable values for goodness of fit as shown by the Nash-Sutcliffe criterion. Groundwater recharge obtained from the successful tests was applied at various spatial and temporal scales to the Kouris and Akrotiri catchments in Cyprus. These recharge values produced good estimates of groundwater levels in both catchments. Once calibrated, the model was run using a number of possible future climate change scenarios. The results showed that by 2050, groundwater and surface water supplies would decrease by 35% and 24% for Kouris and 20% and 17% for Akrotiri, respectively. The gap between water supply and demand showed a linear increase with time. The results suggest that IHMS can be used as an effective tool for water authorities and decision makers to help balance demand and supply on the island. Copyright © 2010 John Wiley & Sons, Ltd. [source] Assessing the results of scenarios of climate and land use changes on the hydrology of an Italian catchment: modelling studyHYDROLOGICAL PROCESSES, Issue 19 2010Daniela R. D'Agostino Abstract Hydrological models are recognized as valid scientific tools to study water quantity and quality and provide support for the integrated management and planning of water resources at different scales. In common with many catchments in the Mediterranean, the study catchment has many problems such as the increasing gap between water demand and supply, water quality deterioration, scarcity of available data, lack of measurements and specific information. The application of hydrological models to investigate hydrological processes in this type of catchments is of particular relevance for water planning strategies to address the possible impact of climate and land use changes on water resources. The distributed catchment scale model (DiCaSM) was selected to study the impact of climate and land use changes on the hydrological cycle and the water balance components in the Apulia region, southern Italy, specifically in the Candelaro catchment (1780 km2). The results obtained from this investigation proved the ability of DiCaSM to quantify the different components of the catchment water balance and to successfully simulate the stream flows. In addition, the model was run with the climate change scenarios for southern Italy, i.e. reduced winter rainfall by 5,10%, reduced summer rainfall by 15,20%, winter temperature rise by 1·25,1·5 °C and summer temperature rise by 1·5,1·75 °C. The results indicated that by 2050, groundwater recharge in the Candelaro catchment would decrease by 21,31% and stream flows by 16,23%. The model results also showed that the projected durum wheat yield up to 2050 is likely to decrease between 2·2% and 10·4% due to the future reduction in rainfall and increase in temperature. In the current study, the reliability of the DiCaSM was assessed when applied to the Candelaro catchment; those parameters that may cause uncertainty in model output were investigated using a generalized likelihood uncertainty estimation (GLUE) methodology. The results showed that DiCaSM provided a small level of uncertainty and subsequently, a higher confidence level. Copyright © 2010 John Wiley & Sons, Ltd. [source] Global perspective on hydrology, water balance, and water resources management in arid basinsHYDROLOGICAL PROCESSES, Issue 2 2010Yanjun Shen Abstract Arid and semiarid regions comprise a large part of the world's terrestrial area and are home to hundreds of millions of people. Water resources in arid regions are rare and critical to society and to ecosystems. The hydrologic cycle in arid and semiarid regions has been greatly altered due to long-term human exploitation. Under conditions of global warming, water resources in these regions are expected to be more unstable and ecosystems likely will suffer from severe water stress. In the current special issue contributed to understanding ecohydrologic processes and water-related problems in arid regions of western China, this paper provides a global perspective on the hydrology and water balance of six major arid basins of the world. A number of global datasets, including the state-of-the-art ensemble simulation of land surface models by GSWP2 (Global Soil Wetness Project II, a project by GEWEX), were used to address the water balance terms in the world's major hydroclimatic regions. The common characteristics of hydrologic cycles and water balance in arid basins are as follows: strong evapotranspiration characterizes the hydrological cycle in arid basins; and in water use sectors irrigation consumes a large amount of water, resulting in degradation of native vegetation. From the ecohydrology viewpoint, a comprehensive study of hydrological and ecological processes of water utilization in arid basins is urgently needed. Copyright © 2009 John Wiley & Sons, Ltd. [source] Modelling lake stage and water balance of Lake Tana, EthiopiaHYDROLOGICAL PROCESSES, Issue 25 2009Yirgalem A. Chebud Abstract The level of Lake Tana, Ethiopia, fluctuates annually and seasonally following the patterns of changes in precipitation. In this study, a mass balance approach is used to estimate the hydrological balance of the lake. Water influx from four major rivers, subsurface inflow from the floodplains, precipitation, outflow from the lake constituting river discharge and evapotranspiration from the lake are analysed on monthly and annual bases. Spatial interpolation of precipitation using rain gauge data was conducted using kriging. Outflow from the lake was identified as the evaporation from the lake's surface as well as discharge at the outlet where the Blue Nile commences. Groundwater inflow is estimated using MODular three-dimensional finite-difference ground-water FLOW model software that showed an aligned flow pattern to the river channels. The groundwater outflow is considered negligible based on the secondary sources that confirmed the absence of lake water geochemical mixing outside of the basin. Evaporation is estimated using Penman's, Meyer's and Thornwaite's methods to compare the mass balance and energy balance approaches. Meteorological data, satellite images and temperature perturbation simulations from Global Historical Climate Network of National Oceanographic and Atmospheric Administration are employed for estimation of evaporation input parameters. The difference of the inflow and outflow was taken as storage in depth and compared with the measured water level fluctuations. The study has shown that the monthly and annually calculated lake level replicates the observed values with root mean square error value of 0·17 and 0·15 m, respectively. Copyright © 2009 John Wiley & Sons, Ltd. [source] Hydrological behaviour and modelling of a volcanic tropical cultivated catchmentHYDROLOGICAL PROCESSES, Issue 22 2008Jean-Baptiste Charlier Abstract The hydrological behaviour of the cultivated Féfé catchment (17·8 ha) on the tropical volcanic island of Guadeloupe was studied to identify flow paths, to quantify water fluxes, and finally, to build a lumped model to simulate discharge and piezometer levels. The approach combined two steps, an experimental step and a modelling step, which covered two time scales, the annual and the storm event scale. The hydrological measurements were conducted over 2 years. The Féfé catchment is characterized by heavy rainfall (4229 mm year,1) on permeable Andosols; the results showed that underground flow paths involved two overlapping aquifers, and that the annual water balance in 2003 was shared among outflows of the deep aquifer (42%), evapotranspiration (31%), and streamflow (27%). On the event scale, the surface runoff coefficient ranges between 6·2% and 24·4% depending on antecedent dry or wet moisture conditions. Hortonian overland flow predominated over subsurface and saturation overland flow processes. Recharge of the shallow aquifer is mainly governed by a constant infiltration capacity of the Andosols with depth in the vadose zone. Outflows of this shallow aquifer were the baseflow of the main stream and the recharge of the deep aquifer. Volcanic deposits at Féfé promoted the underground flow path, and cultivated areas seemed to explain the high stormflow values relative to other tropical small catchments under rain forest. A conceptual lumped model integrating runoff, infiltration, evapotranspiration, and fluctuations of the two overlapping aquifers was developed. The model has six parameters and was calibrated and validated on the hydrograph at the outlet and on the two piezometers of the shallow and the deep aquifers. The results show fair to good agreement between measured and simulated variables, and consequently, the model was consistent with the main hydrological processes observed from experimental results in wet conditions. Copyright © 2008 John Wiley & Sons, Ltd. [source] Hydrogeologic controls on streamflow sensitivity to climate variationHYDROLOGICAL PROCESSES, Issue 22 2008Anne Jefferson Abstract Climate models project warmer temperatures for the north-west USA, which will result in reduced snowpacks and decreased summer streamflow. This paper examines how groundwater, snowmelt, and regional climate patterns control discharge at multiple time scales, using historical records from two watersheds with contrasting geological properties and drainage efficiencies. In the groundwater-dominated watershed, aquifer storage and the associated slow summer recession are responsible for sustaining discharge even when the seasonal or annual water balance is negative, while in the runoff-dominated watershed subsurface storage is exhausted every summer. There is a significant 1 year cross-correlation between precipitation and discharge in the groundwater-dominated watershed (r = 0·52), but climatic factors override geology in controlling the inter-annual variability of streamflow. Warmer winters and earlier snowmelt over the past 60 years have shifted the hydrograph, resulting in summer recessions lasting 17 days longer, August discharges declining 15%, and autumn minimum discharges declining 11%. The slow recession of groundwater-dominated streams makes them more sensitive than runoff-dominated streams to changes in snowmelt amount and timing. Copyright © 2008 John Wiley & Sons, Ltd. [source] Opportunities for manipulating catchment water balance by changing vegetation type on a topographic sequence: a simulation studyHYDROLOGICAL PROCESSES, Issue 6 2008Enli Wang Abstract This simulation study explores opportunities to reduce catchment deep drainage through better matching land use with soil and topography, including the ,harvesting' (evapotranspiration) of excess water running on to lower land units. A farming system simulator was coupled with a catchment hydrological framework to enable analysis of climate variability and 11 different land-use options as they impact the catchment water balance. These land-use options were arranged in different configurations down a sequence of three hydrologically interconnected slope units (uphill, mid-slope and valley floor land units) in a subcatchment of Simmons Creek, southern New South Wales, Australia. With annual crops, the valley floor land units were predicted to receive 187 mm year,1 of run-on water in addition to annual rainfall in 1 in 10 years, and in excess of 94 mm year,1 in 1 in 4 years. In this valley floor position, predicted drainage averaged approximately 110 mm year,1 under annual crops and pastures, whereas permanent tree cover or perennial lucerne was predicted to reduce drainage by up to 99%. The planting of trees or lucerne on the valley floor units could ,harvest' run-on water, reducing drainage for the whole subcatchment with proportionately small reduction in land areas cropped. Upslope land units, even though often having shallower soil, will not necessarily be the most effective locations to plant perennial vegetation for the purposes of recharge reduction. Water harvesting opportunities are site specific, dependent on the amounts and frequency of flows of water to lower landscape units, the amounts and frequency of deep drainage on the different land units, the relative areas of the different land units, and interactions with land use in the different slope positions. Copyright © 2007 John Wiley & Sons, Ltd. [source] Simulating soil-water movement under a hedgerow surrounding a bottomland reveals the importance of transpiration in water balanceHYDROLOGICAL PROCESSES, Issue 5 2008Z. Thomas Abstract The objective of this study was to quantify components of the water balance related to root-water uptake in the soil below a hedgerow. At this local scale, a two-dimensional (2D) flow domain in the x,z plane 6 m long and 1·55 m deep was considered. An attempt was made to estimate transpiration using a simulation model. The SWMS-2D model was modified and used to simulate temporally and spatially heterogeneous boundary conditions. A function with a variable spatial distribution of root-water uptake was considered, and model calibration was performed by adjusting this root-water uptake distribution. Observed data from a previous field study were compared against model predictions. During the validation step, satisfactory agreement was obtained, as the difference between observed and modelled pressure head values was less than 50 cm for 80% of the study data. Hedge transpiration capacity is a significant component of soil-water balance in the summer, when predicted transpiration reaches about 5·6 mm day,1. One of the most important findings is that hedge transpiration is nearly twice that of a forest canopy. In addition, soil-water content is significantly different whether downslope or upslope depending on the root-water uptake. The high transpiration rate was mainly due to the presence of a shallow water table below the hedgerow trees. Soil-water content was not a limiting factor for transpiration in this context, as it could be in one with a much deeper water table. Hedgerow tree transpiration exerts a strong impact not only on water content within the vadose zone but also on the water-table profile along the transect. Results obtained at the local scale reveal that the global impact of hedges at the catchment scale has been underestimated in the past. Transpiration rate exerts a major influence on water balance at both the seasonal and annual scales for watersheds with a dense network of hedgerows. Copyright © 2007 John Wiley & Sons, Ltd. [source] Improvement of the hydrological component of an urban soil,vegetation,atmosphere,transfer modelHYDROLOGICAL PROCESSES, Issue 16 2007A. Lemonsu Abstract A numerical study was conducted on the Rezé suburban catchment (Nantes, France) to evaluate the hydrological component of the town energy balance (TEB) scheme, which simulates in a coupled way the water and energy balances for the urban covers. The catchment is a residential area where hydrological data were continuously collected from 1993 to 1998 by the Laboratoire Central des Ponts et Chaussées (LCPC), notably the runoff in the stormwater drainage network. A 6-year simulation with the TEB and interaction soil,biosphere,atmosphere (ISBA) schemes in off-line mode enabled the comparison of modelled and observed runoff. Some weaknesses of the TEB were uncovered and led to improved parameterization of water exchanges: (1) calibration of the maximum capacity of the rainfall interception reservoir on roads and roofs and (2) inclusion of water infiltration through the roads, according to a simple formulation. The calibration of this water flux gives results that are consistent with direct measurements of water infiltration performed on the Rezé site and from the literature. The new parameterization produces better runoff in terms of timing and magnitude, which are comparable to those obtained by the LCPC with other hydrological models. It shows also the impact of the water infiltration through the roads, corresponding to a water transfer from the TEB to ISBA, on the water balance: the water contents of road, roof and soil reservoirs being modified, the evaporation from artificial surfaces decreases, while the evapotranspiration from natural covers increases. Through the evaporative flux, such a modification of the water balance induces large repercussions on the surface energy balance. Copyright © 2007 John Wiley & Sons, Ltd. [source] Wetlands with controlled drainage and sub-irrigation systems,modelling of the water balanceHYDROLOGICAL PROCESSES, Issue 14 2007Ottfried Dietrich Abstract Over the past centuries, the agricultural use of wetlands in Central Europe has required interference with the natural wetland water balance. Often this has consisted of drainage measures alone. In low-precipitation areas, it has also involved the operation of combined drainage and sub-irrigation systems. Model studies conducted as part of planning processes, or with a view to finding out the impact of changing climate conditions on the water balance of wetlands, must take these facts into account. For this reason, a water balance model has been devised for wetlands whose water balance is governed by water resources management systems. It is based on the WBalMo model system. Special modules were integrated into WBalMo to calculate the water balance of wetland areas (WABI module) and to regulate inflow partitioning within the wetland (REGINF module). When calculating the water balance, the WABI module takes into account precipitation and potential evapotranspiration, groundwater levels below surface, soil types, land-use classes, inflows via the running water system, and data for target water levels. It provides actual evapotranspiration, discharge into the running water system, and groundwater levels in the area. The example of the Spreewald, a major wetland area in north-eastern Germany, was used to design and test the WBalMo Spreewald model. The comparison of measured and calculated water balance parameters of the wetland area confirms the suitability of the model for water balance studies in wetlands with complex water resources management systems. The results reveal the strong influence of water management on the water balance of such areas. The model system has proved to be excellently suited for planning and carrying out water management measures aimed at the sustainable development of wetlands. Furthermore, scenario analyses can be used to assess the impact of global change on the water balance of wetlands. Copyright © 2006 John Wiley & Sons, Ltd. [source] Evaporation estimation on Lake Titicaca: a synthesis review and modellingHYDROLOGICAL PROCESSES, Issue 13 2007François Delclaux Abstract The aim of this study was to validate evaporation models that can be used for palaeo-reconstructions of large lake water levels. Lake Titicaca, located in a high-altitude semi-arid tropical area in the northern Andean Altiplano, was the object of this case study. As annual evaporation is about 90% of lake output, the lake water balance depends heavily on the yearly and monthly evaporation flux. At the interannual scale, evaporation estimation presents great variability, ranging from 1350 to 1900 mm year,1. It has been found that evaporation is closely related to lake rainfall by a decreasing relationship integrating the implicit effect of nebulosity and humidity. At the seasonal scale, two monthly evaporation data sets were used: pan observations and estimations derived from the lake energy budget. Comparison between these data sets shows that (i) there is one maximum per year for pan evaporation and two maxima per year for lake evaporation, and (ii) pan evaporation is greater than lake evaporation by about 100 mm year,1. These differences, mainly due to a water depth scale factor, have been simulated with a simple thermal model ,w(h, t) of a free-surface water column. This shows that pan evaporation (h = 0·20 m) is strongly correlated with direct solar radiation, whereas the additional maximum of lake evaporation (h = 40 m) is related to the heat restitution towards the atmosphere from the water body at the end of summer. Finally, five monthly evaporation models were tested in order to obtain the optimal efficiency/complexity ratio. When the forcing variables are limited to those that are most readily available in the past, i.e. air temperature and solar radiation, the best results are obtained with the radiative Abtew model (r = 0·70) and with the Makkink radiative/air temperature model (r = 0·67). Copyright © 2007 John Wiley & Sons, Ltd. [source] Simulating the response of a closed-basin lake to recent climate changes in tropical West Africa (Lake Bosumtwi, Ghana)HYDROLOGICAL PROCESSES, Issue 13 2007Timothy M. Shanahan Abstract Historical changes in the level of Lake Bosumtwi, Ghana, have been simulated using a catchment-scale hydrological model in order to assess the importance of changes in climate and land use on lake water balance on a monthly basis for the period 1939,2004. Several commonly used models for computing evaporation in data-sparse regions are compared, including the Penman, the energy budget, and the Priestley,Taylor methods. Based on a comparison with recorded lake level variations, the model with the energy-budget evaporation model subcomponent is most effective at reproducing observed lake level variations using regional climate records. A sensitivity analysis using this model indicates that Lake Bosumtwi is highly sensitive to changes in precipitation, cloudiness and temperature. However, the model is also sensitive to changes in runoff related to vegetation, and this factor needs to be considered in simulating lake level variations. Both interannual and longer-term changes in lake level over the last 65 years appear to have been caused primarily by changes in precipitation, though the model also suggests that the drop in lake level over the last few decades has been moderated by changes in cloudiness and temperature over that time. Based on its effectiveness at simulating the magnitude and rate of lake level response to changing climate over the historical record, this model offers a potential future opportunity to examine the palaeoclimatic factors causing past lake level fluctuations preserved in the geological record at Lake Bosumtwi. Copyright © 2006 John Wiley & Sons, Ltd. [source] Water fluxes at a fluctuating water table and groundwater contributions to wheat water use in the lower Yellow River flood plain, ChinaHYDROLOGICAL PROCESSES, Issue 6 2007Jianfeng Yang Abstract Capillary upflow from and deep percolation to a water table may be important in crop water supply in irrigated areas of the lower Yellow River flood plain, north China. These fluxes at the water table and the variations of the capillary upflow in relation to crop evapotranspiration need to be investigated to quantify the effect of a water table on soil water balance and to improve agricultural water management. A large weighing lysimeter was used to determine daily crop evapotranspiration, daily capillary upflow from and daily percolation to a fluctuating water table during a rotation period with wheat growing in a dry season and maize in a rainy season. The water table depth varied in the range 0·7,2·3 m during the maize growth period and 1·6,2·4 m during the wheat growth period. Experimental results showed that the capillary upflow and the percolation were significant components of the soil water balance. Three distinctly different phases for the water fluxes at the water table were observed through the rotation period: water downward period, the period of no or small water fluxes, and water upward period. It implied that the temporal pattern of these water fluxes at the water table was intimately associated with the temporal distribution of rainfall through the rotation period. An empirical equation was determined to estimate the capillary upflow in relation to wheat evapotranspiration and root zone soil water content for local irrigation scheduling. Coupled with the FAO-Penman,Monteith equation, the equation offers a fast and low cost solution to assess the effect of capillary upflow from a water table on wheat water use. Copyright © 2007 John Wiley & Sons, Ltd. [source] Water resources in mountain regions: a methodological approach to assess the water balance in a highland-lowland-systemHYDROLOGICAL PROCESSES, Issue 5 2007Rolf Weingartner Abstract Mountains and highlands are typically areas that provide considerable quantities of water, the latter being an important resource for the lowlands. These run-off quantities remain discernible in the superior-scale river systems and significantly contribute to the global water resources. Therefore, mountain regions ought to be given specific consideration with regard to management endeavours. Although well known in principle, details of water resources originating from mountains remain under discussion. A new approach has been introduced, which depicts the water balance of Switzerland in a spatially distributed manner, based on catchments of about 150 km2. The main feature of this approach is the areal precipitation, which is calculated using run-off, evaporation and storage change of glaciers, instead of being derived from gauged precipitation values. This methodology was selected because measurement and regionalization of precipitation remain subject to large uncertainties in mountainous areas. Subsequently, the view is widened to the European Alps, which, as compared with the surrounding lowlands, contribute considerably higher annual discharge, especially in the summer months. Finally, the focus is put on the hydrological significance of mountains in general. In dry regions, mountains, in particular, are indispensable contributors to the water resources downstream. Copyright © 2006 John Wiley & Sons, Ltd. [source] Riparian influence on hyporheic-zone formation downstream of a small dam in the Blackland Prairie region of TexasHYDROLOGICAL PROCESSES, Issue 2 2007Jacquelyn R. Duke Abstract Small-order streams have highly variable flows that can result in large temporal and spatial variation of the hyporheic zone. Dam construction along these intermittent headwater streams alters downstream flow and influences the hydrologic balance between stream water and the adjacent riparian zone. A 3-year site study was conducted along an impounded second-order stream to determine the water balance between stream, unsaturated zone, groundwater and riparian vegetation. The presence of the upstream impoundment provided near-perennial water flow in the stream channel. The observed woody plant transpiration accounted for 71% of average annual water loss in the site. The overall contribution of stream water via the hyporheic zone to site water balance was 73 cm, or 44% of total inputs. This exceeded both rainfall and upland subsurface contribution to the site. A highly dynamic hyporheic zone was indicated by high water use from woody plants that fluctuated seasonally with stream water levels. We found leaf area development in the canopy layer to be closely coupled with stream and groundwater fluctuations, indicating its usefulness as a potential indicator of site water balance for small dam systems. The net result of upstream impoundment increased riparian vegetation productivity by influencing movement of stream water to storage in the groundwater system. Copyright © 2006 John Wiley & Sons, Ltd. [source] Classification of hydrological regimes of northern floodplain basins (Peace,Athabasca Delta, Canada) from analysis of stable isotopes (,18O, ,2H) and water chemistryHYDROLOGICAL PROCESSES, Issue 2 2007Brent B. Wolfe Abstract We used stable isotopes (,18O and ,2H) and water chemistry to characterize the water balance and hydrolimnological relationships of 57 shallow aquatic basins in the Peace-Athabasca Delta (PAD), northern Alberta, Canada, based on sampling at the end of the 2000 thaw season. Evaporation-to-inflow ratios (E/I) were estimated using an isotope mass-balance model tailored to accommodate basin-specific input water compositions, which provided an effective, first-order, quantitative framework for identifying water balances and associated limnological characteristics spanning three main, previously identified drainage types. Open-drainage basins (E/I < 0·4; n = 5), characterized by low alkalinity, low concentrations of nitrogen, dissolved organic carbon (DOC) and ions, and high minerogenic turbidity, include large, shallow basins that dominate the interior of the PAD and experience frequent or continuous river channel connection. Closed-drainage basins (E/I , 1·0; n = 16), in contrast, possess high alkalinity and high concentrations of nitrogen, DOC, and ions, and low minerogenic turbidity, and are located primarily in the relict and infrequently flooded landscape of the northern Peace sector of the delta. Several basins fall into the restricted-drainage category (0·4 # E/I < 1·0; n = 26) with intermediate water chemistries and are predominant in the southern Athabasca sector, which is subject to active fluviodeltaic processes, including intermittent flooding from riverbank overflow. Integration of isotopic and limnological data also revealed evidence for a new fourth drainage type, mainly located near the large open-drainage lakes that occupy the central portion of the delta but within the Athabasca sector (n = 10). These basins were very shallow (<50 cm deep) at the time of sampling and isotopically depleted, corresponding to E/I characteristic of restricted- and open-drainage conditions. However, they are limnologically similar to closed-drainage basins except for higher conductivity and higher concentrations of Ca2+ and Na+, and lower concentrations of SiO2 and chlorophyll c. These distinct features are due to the overriding influence of recent summer rainfall on the basin water balance and chemistry. The close relationships evident between water balances and limnological conditions suggest that past and future changes in hydrology are likely to be coupled with marked alterations in water chemistry and, hence, the ecology of aquatic environments in the PAD. Copyright © 2006 John Wiley & Sons, Ltd. [source] The impact of groundwater,surface water interactions on the water balance of a mesoscale lowland river catchment in northeastern GermanyHYDROLOGICAL PROCESSES, Issue 2 2007Stefan Krause Abstract The glacially formed northeastern German lowlands are characterized by extensive floodplains, often interrupted by relatively steep moraine hills. The hydrological cycle of this area is governed by the tight interaction of surface water dynamics and the corresponding directly connected shallow groundwater aquifer. Runoff generation processes, as well as the extent and spatial distribution of the interaction between surface water and groundwater, are controlled by floodplain topography and by surface water dynamics. A modelling approach based on extensive experimental analyses is presented that describes the specific water balance of lowland areas, including the interactions of groundwater and surface water, as well as reflecting the important role of time-variable shallow groundwater stages for runoff generation in floodplains. In the first part, experimental investigations of floodplain hydrological characteristics lead to a qualitative understanding of the water balance processes and to the development of a conceptual model of the water balance and groundwater dynamics of the study area. Thereby model requirements which allow for an adequate simulation of the floodplain hydrology, considering also interactions between groundwater and surface water have been characterized. Based on these analyses, the Integrated Modelling of Water Balance and Nutrient Dynamics (IWAN) approach has been developed. This consists of coupling the surface runoff generation and soil water routines of the deterministic, spatially distributed hydrological model WASIM-ETH-I with the three-dimensional finite-difference-based numerical groundwater model MODFLOW and Processing MODFLOW. The model was applied successfully to a mesoscale subcatchment of the Havel River in northeast Germany. It was calibrated for two small catchments (1·4 and 25 km2), where the importance of the interaction processes between groundwater and surface waters and the sensitivity of several controlling parameters could be quantified. Validation results are satisfying for different years for the entire 198 km2 catchment. The model approach was further successfully tested for specific events. The experimental area is a typical example of a floodplain-dominated landscape. It was demonstrated that the lateral flow processes and the interactions between groundwater and surface water have a major importance for the water balance and periodically superimposed on the vertical runoff generation. Copyright © 2006 John Wiley & Sons, Ltd. [source] Use of multi-platform, multi-temporal remote-sensing data for calibration of a distributed hydrological model: an application in the Arno basin, ItalyHYDROLOGICAL PROCESSES, Issue 13 2006Lorenzo Campo Abstract Images from satellite platforms are a valid aid in order to obtain distributed information about hydrological surface states and parameters needed in calibration and validation of the water balance and flood forecasting. Remotely sensed data are easily available on large areas and with a frequency compatible with land cover changes. In this paper, remotely sensed images from different types of sensor have been utilized as a support to the calibration of the distributed hydrological model MOBIDIC, currently used in the experimental system of flood forecasting of the Arno River Basin Authority. Six radar images from ERS-2 synthetic aperture radar (SAR) sensors (three for summer 2002 and three for spring,summer 2003) have been utilized and a relationship between soil saturation indexes and backscatter coefficient from SAR images has been investigated. Analysis has been performed only on pixels with meagre or no vegetation cover, in order to legitimize the assumption that water content of the soil is the main variable that influences the backscatter coefficient. Such pixels have been obtained by considering vegetation indexes (NDVI) and land cover maps produced by optical sensors (Landsat-ETM). In order to calibrate the soil moisture model based on information provided by SAR images, an optimization algorithm has been utilized to minimize the regression error between saturation indexes from model and SAR data and error between measured and modelled discharge flows. Utilizing this procedure, model parameters that rule soil moisture fluxes have been calibrated, obtaining not only a good match with remotely sensed data, but also an enhancement of model performance in flow prediction with respect to a previous calibration with river discharge data only. Copyright © 2006 John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||