Home About us Contact
|
Home About us Contact | ||
|
|
||
Water Balance Model (water + balance_model)
Selected AbstractsModelling variable source area dynamics in a CEAP watershedECOHYDROLOGY, Issue 3 2009Helen E. Dahlke Abstract In the Northeast US, saturation excess is the most dominant runoff process and locations of runoff source areas, typically called variable source areas (VSAs), are determined by the available soil water storage and the landscape topographic position. To predict runoff generated from VSAs some water quality models use the Soil Conservation Service Curve Number equation (SCS-CN), which assumes a constant initial abstraction of rainfall is retained by the watershed prior to the beginning of runoff. We apply a VSA interpretation of the SCS-CN runoff equation that allows the initial abstraction to vary with antecedent moisture conditions. We couple this modified SCS-CN approach with a semi-distributed water balance model to predict runoff, and distribute predictions using a soil topographic index for the Town Brook watershed in the Catskill Mountains of New York State. The accuracy of predicted VSA extents using both the original and the modified SCS-CN equation were evaluated for 14 rainfall-runoff events through a comparison with average water table depths measured at 33 locations in Town Brook from March,September 2004. The modified SCS-CN equation captured VSA dynamics more accurately than the original equation. However, during events with high antecedent rainfall VSA dynamics were still under-predicted suggesting that VSA runoff is not captured solely by knowledge of the soil water deficit. Considering the importance of correctly predicting runoff generation and pollutant source areas in the landscape, the results of this study demonstrate the feasibility of integrating VSA hydrology into water quality models to reduce non-point source pollution. Copyright © 2009 John Wiley & Sons, Ltd. [source] Amazon drought and its implications for forest flammability and tree growth: a basin-wide analysisGLOBAL CHANGE BIOLOGY, Issue 5 2004Daniel Nepstad Abstract Severe drought in moist tropical forests provokes large carbon emissions by increasing forest flammability and tree mortality, and by suppressing tree growth. The frequency and severity of drought in the tropics may increase through stronger El Niño Southern Oscillation (ENSO) episodes, global warming, and rainfall inhibition by land use change. However, little is known about the spatial and temporal patterns of drought in moist tropical forests, and the complex relationships between patterns of drought and forest fire regimes, tree mortality, and productivity. We present a simple geographic information system soil water balance model, called RisQue (Risco de Queimada , Fire Risk) for the Amazon basin that we use to conduct an analysis of these patterns for 1996,2001. RisQue features a map of maximum plant-available soil water (PAWmax) developed using 1565 soil texture profiles and empirical relationships between soil texture and critical soil water parameters. PAW is depleted by monthly evapotranspiration (ET) fields estimated using the Penman,Monteith equation and satellite-derived radiation inputs and recharged by monthly rain fields estimated from 266 meteorological stations. Modeled PAW to 10 m depth (PAW10 m) was similar to field measurements made in two Amazon forests. During the severe drought of 2001, PAW10 m fell to below 25% of PAWmax in 31% of the region's forests and fell below 50% PAWmax in half of the forests. Field measurements and experimental forest fires indicate that soil moisture depletion below 25% PAWmax corresponds to a reduction in leaf area index of approximately 25%, increasing forest flammability. Hence, approximately one-third of Amazon forests became susceptible to fire during the 2001 ENSO period. Field measurements also suggest that the ENSO drought of 2001 reduced carbon storage by approximately 0.2 Pg relative to years without severe soil moisture deficits. RisQue is sensitive to spin-up time, rooting depth, and errors in ET estimates. Improvements in our ability to accurately model soil moisture content of Amazon forests will depend upon better understanding of forest rooting depths, which can extend to beyond 15 m. RisQue provides a tool for early detection of forest fire risk. [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] Comparison of seven models for estimation of evapotranspiration and groundwater recharge using lysimeter measurement data in GermanyHYDROLOGICAL PROCESSES, Issue 18 2005C.-Y. Xu Abstract This study evaluates seven evapotranspiration models and their performance in water balance studies by using lysimeter measurement data at the Mönchengladbach hydrological and meteorological station in Germany. Of the seven evapotranspiration models evaluated, three models calculate actual evapotranspiration directly using the complementary relationship approach, i.e. the CRAE model of Morton, the advection,aridity (AA) model of Brutsaert and Stricker, and the GG model of Granger and Gray, and four models calculate first potential evapotranspiration and then actual evapotranspiration by considering the soil moisture condition. Two of the four potential evapotranspiration models belong to the temperature-based category, i.e. the Thornthwaite model and the Hargreaves model, and the other two belong to the radiation-based category, i.e. the Makkink model and the Priestley,Taylor model. The evapotranspiration calculated by the above seven models, together with precipitation, is used in the water balance model to calculate other water balance components. The results show that, for the calculation of actual evapotranspiration, the GG model and the Makkink model performed better than the other models; for the calculation of groundwater recharge using the water balance approach, the GG model and the AA models performed better; for the simulation of soil moisture content using the water balance approach, four models (GG, Thornthwaite, Makkink and Priestley,Taylor) out of the seven give equally good results. It can be concluded that the lysimeter-measured water balance components, i.e. actual evapotranspiration, groundwater recharge, soil moisture, etc., can be predicted by the GG model and the Makkink model with good accuracy. Copyright © 2005 John Wiley & Sons, Ltd. [source] Validation of ERS scatterometer-derived soil moisture data in the central part of the Duero Basin, SpainHYDROLOGICAL PROCESSES, Issue 8 2005Antonio Ceballos Abstract The objective of this study was to validate the soil moisture data derived from coarse-resolution active microwave data (50 km) from the ERS scatterometer. The retrieval technique is based on a change detection method coupled with a data-based modelling approach to account for seasonal vegetation dynamics. The technique is able to derive information about the soil moisture content corresponding to the degree of saturation of the topmost soil layer (,5 cm). To estimate profile soil moisture contents down to 100 cm depth from the scatterometer data, a simple two-layer water balance model is used, which generates a red noise-like soil moisture spectrum. The retrieval technique had been successfully applied in the Ukraine in a previous study. In this paper, the performance of the model in a semi-arid Mediterranean environment characterized by low annual precipitation (400 mm), hot dry summers and sandy soils is investigated. To this end, field measurements from the REMEDHUS soil moisture station network in the semi-arid parts of the Duero Basin (Spain) were used. The results reveal a significant coefficient of determination (R2 = 0·75) for the averaged 0,100 cm soil moisture profile and a root mean square error (RMSE) of 2·2 vol%. The spatial arrangement of the REMEDHUS soil moisture stations also allowed us to study the influence of the small-scale variability of soil moisture within the ERS scatterometer footprint. The results show that the small-scale variability in the study area is modest and can be explained in terms of texture fraction distribution in the soil profiles. Copyright © 2004 John Wiley & Sons, Ltd. [source] Simulating pan-Arctic runoff with a macro-scale terrestrial water balance modelHYDROLOGICAL PROCESSES, Issue 13 2003Michael A. Rawlins Abstract A terrestrial hydrological model, developed to simulate the high-latitude water cycle, is described, along with comparisons with observed data across the pan-Arctic drainage basin. Gridded fields of plant rooting depth, soil characteristics (texture, organic content), vegetation, and daily time series of precipitation and air temperature provide the primary inputs used to derive simulated runoff at a grid resolution of 25 km across the pan-Arctic. The pan-Arctic water balance model (P/WBM) includes a simple scheme for simulating daily changes in soil frozen and liquid water amounts, with the thaw,freeze model (TFM) driven by air temperature, modelled soil moisture content, and physiographic data. Climate time series (precipitation and air temperature) are from the National Centers for Environmental Prediction (NCEP) reanalysis project for the period 1980,2001. P/WBM-generated maximum summer active-layer thickness estimates differ from a set of observed data by an average of 12 cm at 27 sites in Alaska, with many of the differences within the variability (1,) seen in field samples. Simulated long-term annual runoffs are in the range 100 to 400 mm year,1. The highest runoffs are found across northeastern Canada, southern Alaska, and Norway, and lower estimates are noted along the highest latitudes of the terrestrial Arctic in North America and Asia. Good agreement exists between simulated and observed long-term seasonal (winter, spring, summer,fall) runoff to the ten Arctic sea basins (r = 0·84). Model water budgets are most sensitive to changes in precipitation and air temperature, whereas less affect is noted when other model parameters are altered. Increasing daily precipitation by 25% amplifies annual runoff by 50 to 80% for the largest Arctic drainage basins. Ignoring soil ice by eliminating the TFM sub-model leads to runoffs that are 7 to 27% lower than the control run. The results of these model sensitivity experiments, along with other uncertainties in both observed validation data and model inputs, emphasize the need to develop improved spatial data sets of key geophysical quantities (particularly climate time series) to estimate terrestrial Arctic hydrological budgets better. Copyright © 2003 John Wiley & Sons, Ltd. [source] Reconstruction of a 1436-year soil moisture and vegetation water use history based on tree-ring widths from Qilian junipers in northeastern Qaidam Basin, northwestern ChinaINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 1 2008Zhi-Yong Yin Abstract Tree-ring widths have been used widely in studies of environmental changes and reconstructions of past climate. Eleven tree-ring chronologies of approximately 800,1500 years long were developed from Qilian junipers (Sabina przewalskii Kom.) for northeastern Qaidam Basin, along the margin of the Qinghai,Tibetan Plateau. Previous studies have revealed that water usage stress is the most limiting factor for tree growth in the study region. To evaluate the impact of the combined effects of temperature and precipitation changes over time, we performed water balance modelling using 1955,2002 meteorological data. We found that the tree-ring widths were strongly correlated with variables representing soil moisture conditions obtained from the water balance model. Specifically we considered actual evapotranspiration (AE) to represent the combined effect of water use demand and moisture availability, deficit as the difference between potential evapotranspiration (PE) and AE to represent the severity of water use stress, and relative soil moisture as the measure of moisture availability. For certain individual monthly and seasonal combinations, the tree-ring chronologies explained up to 80% of the variation in the soil moisture variables in regression analysis, indicating very good potential for reconstruction of regional soil moisture conditions in the past. These soil moisture variables outperformed precipitation and Palmer's drought severity index in most cases. We reconstructed the soil moisture conditions from 566 AD to 2001, which revealed major dry and wet periods and a general trend toward a wetter condition during the most recent 300 years. By comparing with other proxies in the region, we concluded that the moisture conditions reconstructed from tree-ring widths very well reflected the climate variability at the interannual and interdecadal scales. Copyright © 2007 Royal Meteorological Society [source] Modelling natural conditions and impacts of consumptive water use and sedimentation of Lake Abaya and Lake Chamo, EthiopiaLAKES & RESERVOIRS: RESEARCH AND MANAGEMENT, Issue 2 2006Seleshi Bekele Awulachew Abstract There is few available information regarding the water resource systems of Abaya Lake and Chamo Lake, which are found in the Southern Rift Valley Region of Ethiopia. This paper describes modelling of the water balance components of these lakes, as well as the impacts of water uses, and sediment transport and deposition in the lakes. The various parameters and data needed for the water balance model are derived on the basis of various surveys, analysis of data and modelling efforts. The watershed characteristics are derived using geographical information system, whereas the morphometry of the lakes is investigated by undertaking bathymetry surveys. The hydrometeorological components of this lake system also were investigated through the development of relevant database and information systems, by identifying regional relationships, and by a rainfall-run-off model. These information systems have subsequently been integrated to model the water balance of the two lakes, and simulating the in-lake water levels. Several scenarios reflecting the natural conditions, water consumptive development possibilities, and sedimentation impacts have been investigated in this study. Based on the model simulation results, and on the computation of the life expectancies of the two lakes, it was found that sediment inflow and deposition significantly threaten their existence. [source] Water balance modelling of (Sub-)Arctic rivers and freshwater supply to the Barents Sea BasinPERMAFROST AND PERIGLACIAL PROCESSES, Issue 3 2005Eduard Koster Abstract Recently, changes in the freshwater supply by rivers to the Arctic Ocean have attracted a great deal of attention. However, quantitative assessments of changes in the annual and seasonal discharge regime of (Sub-)Arctic rivers resulting from climate change are still far from accurate. The sensitivity of discharge to potential changes in climate in two river catchments of intermediate size (104,105,km2), the Tana River in northern Fennoscandia and the Usa River in northern Russia, both draining into the Barents Sea Basin, was evaluated using a spatially distributed water balance model. The tentative results show that discharge amounts during peak flow might remain more or less the same or show a slight increase. However, peakflow events are expected to occur about 20 days or more earlier in spring. Concerning annual discharge amounts a strong increase of 25% for the Usa River and even 39% for the Tana River is simulated in conformity with projected increases in precipitation. Obviously, the resulting increases of the annual freshwater influx from the Tana River (from 5.3 to 7.3,km3) and that of the Usa River (from 42 to 52,km3) into the Barents Sea are insignificant in absolute terms. But in relative terms they agree remarkably well with earlier estimates of changes in freshwater inflow by the very large (Sub-)Arctic rivers. Copyright © 2005 John Wiley & Sons, Ltd. [source] Surface water balance to evaluate the hydrological impacts of small instream diversions and application to the Russian River basin, California, USAAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 3 2009Matthew J. Deitch 1.Small streams are increasingly under pressure to meet water needs associated with expanding human development, but the hydrologic and ecological effects are not commonly described in scientific literature. 2.To evaluate the potential effects that surface water abstraction can have on flow regime, scientists and resource managers require tools that compare abstraction to stream flow at ecologically relevant time scales. 3.The classic water balance model was adapted to evaluate how small instream diversions can affect catchment stream-flow; the adapted model maintains the basic mass balance concept, but limits the parameters and considers surface water data at an appropriate timescale. 4.This surface water balance was applied to 20 Russian River tributaries in north-central California to evaluate how recognized diversions can affect stream flow throughout the region. 5.The model indicates that existing diversions have little capacity to influence peak or base flows during the rainy winter season, but may reduce stream flow during spring by 20% in one-third of all the study streams; and have the potential to accelerate summer intermittence in 80% of the streams included in this study. 6.The surface water balance model may be especially useful for guiding river restoration from a hydrologic perspective: it can distinguish among streams with high diversion regimes that may require more than just physical channel restoration to provide ecological benefits, and can illustrate the extent to which changing the diversion parameters of particular water users can affect the persistence of a natural flow regime. 7.As applied to Russian River tributaries, the surface water balances suggest that reducing demand for stream flow in summer may be as important as physical channel restoration to restoring anadromous salmonids in this region. Copyright © 2009 John Wiley & Sons, Ltd. [source] Ecohydrological effects of grazing-induced degradation in the Patagonian Monte, ArgentinaAUSTRAL ECOLOGY, Issue 5 2009ALEJANDRO JORGE BISIGATO Abstract Water-limited ecosystems have undergone rapid change as a consequence of changing land use and climate. The consequences of these changes on soil quality and vegetation dynamics have been documented in different regions of the world. In contrast, their effects on soil water, the most limiting resource in these environments, have received less attention, although in recent years increasing efforts have been made to relate grazing, soil water and vegetation functioning. In this paper, we present the results of field observations of plant phenology and soil water content carried out during two successive years at four sites along a degradation gradient caused by grazing in the Patagonian Monte, Argentina. We also developed a simplified soil water balance model to evaluate how changes in plant cover could affect water balance. Our field observations showed that the soil water content in the soil layer where roots of grasses are abundant (0,25 cm) was higher and the growing cycles were longer in degraded than in preserved sites. Similarly, our modelling approach showed that the deep soil (depth > 10 cm) was wetter in the degraded than in the preserved situation. Simulation also suggested a switch from transpiration to a direct evaporation dominance of water losses with degradation. Although reductions in plant cover related to grazing degradation were associated with a decrease in annual transpiration, the simulated soil water loss by transpiration was higher during summer in the degraded than in the well preserved situation. Thus, our field observations seem to be a consequence of ecohydrological changes causing an accumulation of water in the soil profile during the cold season and its transpiration during summer. In conclusion, our results showed that changes in plant cover caused by grazing disturbance can alter the soil water balance, which in turn can affect vegetation function. [source] Impacts of climate change on lower Murray irrigation,AUSTRALIAN JOURNAL OF AGRICULTURAL & RESOURCE ECONOMICS, Issue 3 2009Jeff Connor This article evaluates irrigated agriculture sector response and resultant economic impacts of climate change for a part of the Murray Darling Basin in Australia. A water balance model is used to predict reduced basin inflows for mild, moderate and severe climate change scenarios involving 1, 2 and 4°C warming, and predict 13, 38 and 63% reduced inflows. Impact on irrigated agricultural production and profitability are estimated with a mathematical programming model using a two-stage approach that simultaneously estimates short and long-run adjustments. The model accounts for a range of adaptive responses including: deficit irrigation, temporarily following of some areas, permanently reducing the irrigated area and changing the mix of crops. The results suggest that relatively low cost adaptation strategies are available for a moderate reduction in water availability and thus costs of such a reduction are likely to be relatively small. In more severe climate change scenarios greater costs are estimated. Adaptations predicted include a reduction in total area irrigated and investments in efficient irrigation. A shift away from perennial to annual crops is also predicted as the latter can be managed more profitably when water allocations in some years are very low. [source] | |||||||||||||