Water Budget Components Research Articles

Alterações nas trocas interaquíferas resultantes de bombeamento a longo prazo: implicações para a recarga de águas subterrâneas em leito de rocha

Extensive pumping of aquifer systems alters the water budget components for individual aquifer units. This study evaluated long-term changes in alluvial-bedrock groundwater exchange within a highly pumped region of the Denver Basin Aquifer System, Colorado (USA). For a data set spanning five decades, bedrock-aquifer water levels were compared to the elevation of mapped stream alluvium in three-dimensional space, providing a description of spatiotemporal changes in the relationship between the alluvial and bedrock aquifers. Results clearly show increased downward hydraulic gradients (from the alluvial aquifer to underlying sedimentary bedrock); thus, recharge to the bedrock aquifer has increased over time. Variably saturated flow modeling was performed to investigate the dependence of recharge on the bedrock aquifer’s water-table position. Model simulations with realistic geologic heterogeneity demonstrate the potential for unsaturated conditions within the bedrock aquifer, which may eventually produce a hydraulic disconnection between the alluvial and bedrock aquifers, limiting further pumping-induced changes in recharge. These results have important implications for understanding and forecasting long-term water-budget changes in aquifer systems subjected to high pumping stress, especially those in semi-arid regions.

Impact of Surface Albedo Assimilation on Snow Estimation

Surface albedo has a significant impact in determining the amount of available net radiation at the surface and the evolution of surface water and energy budget components. The snow accumulation and timing of melt, in particular, are directly impacted by the changes in land surface albedo. This study presents an evaluation of the impact of assimilating Moderate Resolution Imaging Spectroradiometer (MODIS)-based surface albedo estimates in the Noah multi-parameterization (Noah-MP) land surface model, over the continental US during the time period from 2000 to 2017. The evaluation of simulated snow depth and snow cover fields show that significant improvements from data assimilation (DA) are obtained over the High Plains and parts of the Rocky Mountains. Earlier snowmelt and reduced agreements with reference snow depth measurements, primarily over the Northeast US, are also observed due to albedo DA. Most improvements from assimilation are observed over locations with moderate vegetation and lower elevation. The aggregate impact on evapotranspiration and runoff from assimilation is found to be marginal. This study also evaluates the relative and joint utility of assimilating fractional snow cover and surface albedo measurements. Relative to surface albedo assimilation, fractional snow cover assimilation is found to provide smaller improvements in the simulated snow depth fields. The configuration that jointly assimilates surface albedo and fractional snow cover measurements is found to provide the most beneficial improvements compared to the univariate DA configurations for surface albedo or fractional snow cover. Overall, the study also points to the need for improving the albedo formulations in land surface models and the incorporation of observational uncertainties within albedo DA configurations.

Conserving Land–Atmosphere Synthesis Suite (CLASS)

AbstractAccurate estimates of terrestrial water and energy cycle components are needed to better understand climate processes and improve models’ ability to simulate future change. Various observational estimates are available for the individual budget terms; however, these typically show inconsistencies when combined in a budget. In this work, a Conserving Land–Atmosphere Synthesis Suite (CLASS) of estimates of simultaneously balanced surface water and energy budget components is developed. Individual CLASS variable datasets, where possible, 1) combine a range of existing variable product estimates, and hence overcome the limitations of estimates from a single source; 2) are observationally constrained with in situ measurements; 3) have uncertainty estimates that are consistent with their agreement with in situ observations; and 4) are consistent with each other by being able to solve the water and energy budgets simultaneously. First, available datasets of a budget variable are merged by implementing a weighting method that accounts both for the ability of datasets to match in situ measurements and the error covariance between datasets. Then, the budget terms are adjusted by applying an objective variational data assimilation technique (DAT) that enforces the simultaneous closure of the surface water and energy budgets linked through the equivalence of evapotranspiration and latent heat. Comparing component estimates before and after applying the DAT against in situ measurements of energy fluxes and streamflow showed that modified estimates agree better with in situ observations across various metrics, but also revealed some inconsistencies between water budget terms in June over the higher latitudes. CLASS variable estimates are freely available viahttps://doi.org/10.25914/5c872258dc183.

Climate change or irrigated agriculture \u2013 what drives the water level decline of Lake Urmia

Lake Urmia is one of the largest hypersaline lakes on earth with a unique biodiversity. Over the past two decades the lake water level declined dramatically, threatening the functionality of the lake’s ecosystems. There is a controversial debate about the reasons for this decline, with either mismanagement of the water resources, or climatic changes assumed to be the main cause. In this study we quantified the water budget components of Lake Urmia and analyzed their temporal evolution and interplay over the last five decades. With this we can show that variations of Lake Urmia’s water level during the analyzed period were mainly triggered by climatic changes. However, under the current climatic conditions agricultural water extraction volumes are significant compared to the remaining surface water inflow volumes. Changes in agricultural water withdrawal would have a significant impact on the lake volume and could either stabilize the lake, or lead to its complete collapse.

Selective Cropping as a Soil Conservation Practice: A Benefits Evaluation

HighlightsReplacing either a winter wheat or corn system with a spring wheat system improved soil retention by more than 19%.When grown for bioenergy production instead of forage hay, switchgrass improved soil retention by 40%.Replacement of field cropping systems with grassland systems improved soil retention by over 70%.Incorporating the environmental merits and demerits of cropping systems during on-farm and policy decision-making may go a long way toward ensuring food, feed, and energy security and environmental sustainability.Abstract. While policies that take land out of production provide a quick fix to erosion, the sustainability of such approaches has been questioned, particularly with the increasing demand for arable land. Policies that reconcile the needs for food, feed, fuel, and healthy ecosystems provide a more sustainable alternative approach to soil erosion management in agricultural lands. This study evaluates the impacts of such a policy that prioritizes the implementation of cropping systems with relatively high environmental benefits. The effectiveness of three field cropping systems and three grassland systems in reducing soil erosion is examined on a 6.6 ha field plot in central Texas over a 20-year period. Soil loss rates under each system are estimated using the Agricultural Policy/Environmental eXtender (APEX) model. A relational comparison of the simulated soil losses and water budget components is undertaken to determine the impact of alternative cropping and grassland systems on the landscape’s hydrologic and erosion processes. The results revealed that replacing a winter wheat system and a corn cropping system with a spring wheat system improved soil retention by 19% and 25%, respectively. Growing switchgrass for bioenergy production instead of forage hay improved soil retention considerably (by 40%). Irrespective of the grassland system adopted (restoration to native prairie or growing switchgrass for hay or bioenergy), the replacement of corn or wheat cropping systems with grassland systems increased soil retention by over 70%. This study shows that there is an opportunity to alleviate concerns about conservation programs that take cropland out of production and those that use food crops as fuel and feedstocks, while considerably reducing soil loss from agricultural lands. Incorporating the merits and demerits of cropping systems and why one system should be preferred over another during on-farm and policy decision-making may go a long way toward ensuring food, feed, and energy security and environmental sustainability. Keywords: Cropping systems, Soil retention, Sustainability, Switchgrass.

Evapotranspiration Reconstruction Based on Land Surface Models and Observed Water Budget Components While Considering Irrigation

AbstractThe accurate estimation of evapotranspiration (ET) is essential for understanding the land surface–atmosphere interaction; however, current ET products have large uncertainties, and irrigation effects on ET are not well represented. In this study, the monthly ET was reconstructed (ETrecon) from GLDAS land surface models (LSMs) over the Yellow River basin of China, which was achieved by using observation-based precipitation, naturalized streamflow, and downscaled consumed irrigation water from the census annual data via an irrigation scheme. The results showed that the monthly ETrecon series were generally improved relative to the original LSM-based ET, with improvements in the correlation coefficient, Nash–Sutcliffe efficiency, mean absolute error, and root-mean-square error by 0.6%–1.8%, 1.2%–14.6%, 1.3%–21.0%, and 2.1%–20.4%, respectively. The ETrecon results were also superior to the collected ET synthesis products in terms of statistics, with generally higher peak values occurring in ETrecon. Regarding the annual time scale, the ETrecon values were close to the water balance ET values, which have been widely used as benchmark data. The interannual variability in ETrecon was good overall and was associated with the LSM precipitation variability and partitioning of precipitation into ET and runoff. The reconstruction method can provide an alternative ET estimate for other river basins. This study will also be valuable for studies and applications in climate change evaluation, drought assessment, and water resources management.

Systematic Hydrological Evaluation of the Noah-MP Land Surface Model over China

We evaluate water budget components—namely, soil moisture, runoff, evapotranspiration, and terrestrial water storage (TWS)—simulated by the Noah land surface model with multi-parameterization options (Noah-MP) in China, a large geographic domain challenging for hydrological modeling due to poor observational data and a lack of one single parameterization that can fit for complex hydrological processes. By comparing the model simulations with multi-source reference data, we show that Noah-MP can generally reproduce the overall spatiotemporal patterns of runoff and evapotranspiration over six major river basins, with the annual correlation coefficients generally greater than 0.8 and the Nash-Sutcliffe model efficiency coefficient exceeding 0.5. Among the six basins evaluated, the best model performance is seen over the Huaihe River basin. The temporal trend of the modeled TWS anomalies agrees well with GRACE (Gravity Recovery and Climate Experiment) observations, capturing major flood and drought events in different basins. Experiments with 12 selected physical parameterization options show that the runoff parameterization has a stronger impact on the simulated soil moisture-runoff-evapotranspiration relationships than the soil moisture factor for stomatal resistance schemes, a result consistent with previous studies. Overall, Noah-MP driven by GLDAS forcing simulates the hydrological variables well, except for the Songliao basin in northeastern China, likely because this is a transitional region with extensive freeze-thaw activity, while representations of human activities may also help improve the model performance.

The Role of the Unsaturated Zone for Rainwater Retention and Runoff at a Drained Wetland Site

Drained wetland sites with shallow water tables cover large parts of Central and Western European lowlands. Their hydrological behaviour is complex and depends on their specific characteristics. In this paper, we analysed how the water budget components of such areas behaved when undergoing rainfall events with amounts greater than 10 mm. All the water budget components were determined using a weighable groundwater lysimeter that was installed in the Spreewald wetland, Germany. On average, 69% of the rainfall was stored in the wetland, while only 8% was discharged and 23% was dissipated by evapotranspiration during the time of the runoff process during and after the rainfall event. More than half of the water that was stored could be attributed to storage within the unsaturated zone, while only a minor part was due to the water storage change under quasi-equilibrium conditions. Hence, the soil moisture depletion in the unsaturated zone in the period before the rainfall had a big influence on the site’s available water storage capacity. The findings show that models and approaches assuming hydrostatic conditions might strongly underestimate the water storage capacity of shallow water table sites and, consequently, overestimate the runoff. Hence, the hydrostatic assumption does not describe the process dynamics of these sites in an appropriate manner.

Human-Induced Alterations to Land Use and Climate and Their Responses for Hydrology and Water Management in the Mekong River Basin

The Mekong River Basin (MRB) is one of the significant river basins in the world. For political and economic reasons, it has remained mostly in its natural condition. However, with population increases and rapid industrial growth in the Mekong region, the river has recently become a hotbed of hydropower development projects. This study evaluated these changing hydrological conditions, primarily driven by climate as well as land use and land cover change between 1992 and 2015 and into the future. A 3% increase in croplands and a 1–2% decrease in grasslands, shrublands, and forests was evident in the basin. Similarly, an increase in temperature of 1–6 °C and in precipitation of 15% was projected for 2015–2099. These natural and climate-induced changes were incorporated into two hydrological models to evaluate impacts on water budget components, particularly streamflow. Wet season flows increased by up to 10%; no significant change in dry season flows under natural conditions was evident. Anomaly in streamflows due to climate change was present in the Chiang Saen and Luang Prabang, and the remaining flow stations showed up to a 5% increase. A coefficient of variation <1 suggested no major difference in flows between the pre- and post-development of hydropower projects. The results suggested an increasing trend in streamflow without the effect of dams, while the inclusion of a few major dams resulted in decreased river streamflow of 6% to 15% possibly due to irrigation diversions and climate change. However, these estimates fall within the range of uncertainties in natural climate variability and hydrological parameter estimations. This study offers insights into the relationship between biophysical and anthropogenic factors and highlights that management of the Mekong River is critical to optimally manage increased wet season flows and decreased dry season flows and handle irrigation diversions to meet the demand for food and energy production.

Assessment and validation of total water storage in the Chesapeake Bay watershed using GRACE

The Chesapeake Bay is the largest estuary in the United States, and its catchment has heterogeneous hydrological and geomorphologic characteristics. It includes seven major river basins: James, Patuxent, Potomac, Rappahannock, Susquehanna, Western Shore, Eastern Shore, and York. Remote sensing data, along with in-situ observations of streamflow and simulated water budget components, can provide significant understanding of variability in water resources availability in this diverse watershed. In this study, we quantify the terrestrial water storage using both remote sensing and in-situ data and hydrologic model outputs in the Chesapeake Bay watershed. Total water storage change (TWSC) was calculated based on the combination of three methods to identify the best approach in estimating TWSC. These methods evaluated different sources of data, including Parameter elevation Regression on Independent Slopes Model (PRISM) precipitation, MODIS ET, U.S. Geological Survey observed streamflow, and the Variable Infiltration Capacity (VIC) model. Estimated TWSC were in close agreement with GRACE-derived TWSC when we employed VIC-simulated streamflow after calibration with observed streamflow. However, the use of VIC-simulated ET or MODIS-derived ET yielded similar results for TWSC. Assessment of TWSC during extreme events (drought) during the summer months revealed that predicting ET is critical for TWSC in June–August and that VIC-simulated TWSC could be a reliable proxy for GRACE data to assess the water availability in the watershed.

Evaluating the uncertainty of terrestrial water budget components over High Mountain Asia.

This study explores the uncertainties in terrestrial water budget estimation over High Mountain Asia (HMA) using a suite of uncoupled land surface model (LSM) simulations. The uncertainty in the water balance components of precipitation (P), evapotranspiration (ET), runoff(R), and terrestrial water storage (TWS) is significantly impacted by the uncertainty in the driving meteorology, with precipitation being the most important boundary condition. Ten gridded precipitation datasets along with a mix of model-, satellite-, and gauge-based products, are evaluated first to assess their suitability for LSM simulations over HMA. The datasets are evaluated by quantifying the systematic and random errors of these products as well as the temporal consistency of their trends. Though the broader spatial patterns of precipitation are generally well captured by the datasets, they differ significantly in their means and trends. In general, precipitation datasets that incorporate information from gauges are found to have higher accuracy with low Root Mean Square Errors and high correlation coefficient values. An ensemble of LSM simulations with selected subset of precipitation products is then used to produce the mean annual fluxes and their uncertainty over HMA in P, ET, and R to be 2.11±0.45, 1.26±0.11, and 0.85±0.36 mm per day, respectively. The mean annual estimates of the surface mass (water) balance components from this model ensemble are comparable to global estimates from prior studies. However, the uncertainty/spread of P, ET, and R is significantly larger than the corresponding estimates from global studies. A comparison of ET, snow cover fraction, and changes in TWS estimates against remote sensing-based references confirms the significant role of the input meteorology in influencing the water budget characterization over HMA and points to the need for improving meteorological inputs.

Impacts of Hydrological Changes on Annual Runoff Distribution in Seasonally Dry Basins

Runoff is expected to change due to climate and land use change. Because it constitutes a large component of the terrestrial water budget, we need to develop new policies for managing regional water resources. To do so, we must first attribute changes in the natural flow regime to either climate or land use change. In this context, the Budyko’s curve has previously been adopted to separate the impacts of climate and land use change on runoff by using long term hydrological variables. In this study, a framework based on Fu’s equation (which describes Budyko’s curve) is used to separate the impacts of climate and land use change on annual runoff distributions. Specifically, this framework is based on a recently developed method to obtain annual runoff probability density function (pdf) in seasonally dry basins—such as those in Mediterranean regions—from climate statistics and Fu’s equation parameter ω. The effect of climate change is captured through variations in the first order statistics of annual rainfall and potential evapotranspiration, while land use change is represented by changes in Fu’s equation parameter ω. The effects of these two drivers (i.e., climate and land use change) are analyzed by reconstructing the annual runoff pdfs for the current period and for likely future scenarios, based on predictions from global circulation models and urbanization trajectories. The results show that climate change can lead to a strong reduction in mean annual runoff, a shift of the runoff pdf toward lower values, and a decrease in its variance. Concurrent changes in climate and land use almost always result in a reduction in the mean annual runoff, due to the greater impact of climate change on the runoff pdf.

Dominant Influencing Factors of Groundwater Recharge Spatial Patterns in Ergene River Catchment, Turkey

Groundwater is of great significance in sustaining life on planet earth. The reliable estimation of groundwater recharge is the key understanding the groundwater reservoir and forecasting its potential accessibility. The main objective of this study was to assess the groundwater recharge and its controlling factors at the Ergene river catchment. A grid-based water balance model was adopted to determine the spatially distributed long-term groundwater recharge and other water budget components, relying upon the hydro-climatic variables, land-use, soil, geology, and relief of the investigated area. The model calculations were performed for the hydrological reference horizon of 20 years at a spatial resolution of 100 × 100 m. The base flow index (BFI) separation concept was applied to split up the simulated total runoff into groundwater recharge and direct runoff. Subsequently, the statistical methods of Pearson product–moment correlation and principal component analysis (PCA) were combined for identifying the dominant catchment and meteorological factors influencing the recharge. The average groundwater recharge over the investigated area amounts to 95 mm/year. The model validation and statistical analysis indicate that the difference between simulated and observed total runoff and recharge values is generally under 20% and no significant inconsistency was observed. PCA indicated that recharge is controlled, in order of significance, by land-use, soil, and climate variables. The findings of this research highlight the key role of spatial variables in recharge determination. In addition, the generated outputs may contribute to groundwater resource management in the Ergene river catchment.

Implications of Improved Representation of Convection for the East Africa Water Budget Using a Convection-Permitting Model

Abstract The precipitation and diabatic heating resulting from moist convection make it a key component of the atmospheric water budget in the tropics. With convective parameterization being a known source of uncertainty in global models, convection-permitting (CP) models are increasingly being used to improve understanding of regional climate. Here, a new 10-yr CP simulation is used to study the characteristics of rainfall and atmospheric water budget for East Africa and the Lake Victoria basin. The explicit representation of convection leads to a widespread improvement in the intensities and diurnal cycle of rainfall when compared with a parameterized simulation. Differences in large-scale moisture fluxes lead to a shift in the mean rainfall pattern from the Congo to Lake Victoria basin in the CP simulation—highlighting the important connection between local changes in the representation of convection and larger-scale dynamics and rainfall. Stronger lake–land contrasts in buoyancy in the CP model lead to a stronger nocturnal land breeze over Lake Victoria, increasing evaporation and moisture flux convergence (MFC), and likely unrealistically high rainfall. However, for the mountains east of the lake, the CP model produces a diurnal rainfall cycle much more similar to satellite estimates, which is related to differences in the timing of MFC. Results here demonstrate that, while care is needed regarding lake forcings, a CP approach offers a more realistic representation of several rainfall characteristics through a more physically based realization of the atmospheric dynamics around the complex topography of East Africa.

Response of the daily transpiration of a larch plantation to variation in potential evaporation, leaf area index and soil moisture

Tree transpiration (T) is a major water budget component and varies widely due to the integrated effects of many environmental and vegetation factors. This study aimed to separate, quantify, and then integrate the effects of the main individual factors, to improve water use estimation and manage the hydrological impacts of forests. A field study was conducted at 3 plots of larch (Larix principis-rupprechtii) plantation in the semi-humid area of the Liupan Mountains, northwest China. The main influencing factors were the atmospheric evaporative demand expressed by potential evapotranspiration (PET), the soil water availability expressed by volumetric soil moisture (VSM) within the 0–100 cm layer, and the canopy transpiration capacity expressed by forest canopy leaf area index (LAI). The daily stand T was estimated through the up-scaling of sap-flow data from sampled trees. It displayed a high degree of scattering in response to PET, VSM and LAI, with an average of 0.76 mm·day−1 and range of 0.01–1.71 mm·day−1 in the growing season of 2014. Using upper boundary lines of measured data, the response tendency of T to each factor and corresponding function type were determined. The T increases firstly rapidly with rising PET, VSM and LAI, then gradually and tends to be stable when the threshold of PET (3.80 mm·day−1), VSM (0.28 m3·m−3) and LAI (3.7) is reached. The T response follows a quadratic equation for PET and saturated exponential function for VSM and LAI. These individual factor functions were coupled to form a general daily T model which was then fitted using measured data as: T = (0.793PET − 0.078PET2)·(1 − exp(−0.272LAI))·(1 − exp(−9.965VSM)). It can well explain the daily T variation of all 3 plots (R2 = 0.86–0.91), and thus can be used to predict the response of daily T of larch stands to changes in both environmental and canopy conditions.

Assessment of Groundwater Recharge, Evaporation, and Runoff in the Drava Basin in Hungary with the WetSpass Model

The assessment of spatial and temporal distribution of groundwater recharge is required as an input to develop the regional groundwater model in the Drava flood plain for more accurate simulations of different management scenarios. WetSpass-M, a GIS-based spatially-distributed water balance model, was implemented to assess monthly, seasonal, and the annual averages of groundwater recharge, surface runoff and actual evapotranspiration in the Drava basin, Hungary for the period between 2000–2018. The basic relevant input-data for the Wetspass-M model is prepared in grid-maps using the tool ARCGIS tool. It comprises monthly climatological recordings (e.g., rainfall, temperature, wind speed), distributed land cover, soil map, groundwater depth, topography, and slope. The long-term temporal and spatial average monthly precipitation (58 mm) is distributed as 29% (17 mm) surface runoff, 27% (16 mm) actual evapotranspiration, and 44% (25 mm) groundwater recharge. The mean annual groundwater recharge, actual evapotranspiration, and surface runoff were 307, 190, and 199 mm, respectively. The findings of the WetSpass-M model are intended to support integrated groundwater modeling. The analysis of simulation results shows that WetSpass-M model works properly to simulate hydrological water budget components in the Drava basin. Moreover, a better understanding of the simulated long-term average spatial distribution about water balance components is useful for managing and planning the available water resources in the Drava basin.

Rainfall partitioning varies across a forest age chronosequence in the southernAppalachianMountains

AbstractEvaporation of precipitation from plant surfaces, or interception, is a major component of the global water budget. Interception has been measured and/or modelled across a wide variety of forest types; however, most studies have focused on mature, second‐growth forests, and few studies have examined interception processes across forest age classes. We present data on two components of interception, total canopy interception (Ei) and litter interception—that is, Oi + Oehorizon layers—(Eff), across a forest age chronosequence, from 2 years since harvest to old growth. We used precipitation, throughfall, and stemflow collectors to measure total rainfall (P) and estimateEi; and collected litter biomass and modelled litter wetting and drying to estimate evaporative loss from litter. CanopyEi,Pminus throughfall, increased rapidly with forest age and then levelled off to a maximum of 21% ofPin an old‐growth site. Stemflow also varied across stands, with the highest stemflow (~8% ofP) observed in a 12‐year‐old stand with high stem density. ModelledEffwas 4–6% ofPand did not vary across sites. Total stand‐level interception losses (Ei + Eff) were best predicted by stand age (R2 = 0.77) rather than structural parameters such as basal area (R2 = 0.49) or leaf area (R2 < 0.01). Forest age appears to be an important driver of interception losses from forested mountain watersheds even when stand‐level structural variables are similar. These results will contribute to our understanding of water budgets across the broader matrix of forest ages that characterize the modern forest landscape.

Modeling Riparian Restoration Impacts on the Hydrologic Cycle at the Babacomari Ranch, SE Arizona, USA

This paper describes coupling field experiments with surface and groundwater modeling to investigate rangelands of SE Arizona, USA using erosion-control structures to augment shallow and deep aquifer recharge. We collected field data to describe the physical and hydrological properties before and after gabions (caged riprap) were installed in an ephemeral channel. The modular finite-difference flow model is applied to simulate the amount of increase needed to raise groundwater levels. We used the average increase in infiltration measured in the field and projected on site, assuming all infiltration becomes recharge, to estimate how many gabions would be needed to increase recharge in the larger watershed. A watershed model was then applied and calibrated with discharge and 3D terrain measurements, to simulate flow volumes. Findings were coupled to extrapolate simulations and quantify long-term impacts of riparian restoration. Projected scenarios demonstrate how erosion-control structures could impact all components of the annual water budget. Results support the potential of watershed-wide gabion installation to increase total aquifer recharge, with models portraying increased subsurface connectivity and accentuated lateral flow contributions.

Assessment of Field Water Budget Components for Increasing Water Productivity Under Drip Irrigation in Arid and Semi‐Arid Areas, Syria

AbstractWater shortage and global water demand in arid and semi‐arid countries are continuously increasing, and therefore the agricultural sector is under critical pressure. Sustainable water management is a crucial issue and needs detailed investigation. Lysimeter measurement and nuclear techniques have been used to improve water management, saving water by reducing loss components which are not used by the plants and thus enhance water productivity (WP). Two experimental sites were selected at Nashabieh and Serghaya in the Damascus Basin (Syria). Monitoring of soil water content, evaporation and deep percolation measurements were carried out. The results showed that the measured deep percolation in a maize field (Nashabieh) formed 20% of the applied drip irrigation. On average, volumetric water content increased with depth from 30 to 37% in the apple orchard field under drip irrigation (Serghaya). Water component distribution reveals that 10–20% of water can be saved and used to enhance WP. The computed WP of maize crop was 1.4 kg m−3. Thus the surface drip irrigation method increases WP significantly. Consequently, the application of this irrigation method at the farm scale is highly recommended. Finally, these results may help to develop better agricultural water management strategies, increase agriculture productivity, and consequently improve WP. © 2019 John Wiley & Sons, Ltd.

Estimation of Water Budget Components of the Sakarya River Basin by Using the WEAP-PGM Model

The use of water resources has increased with rapid population growth, industrial development, and agricultural activities. Besides, the problem might increase with the potential climate change impacts on water quantity. Thus, sustainable use of water resources becomes crucial. Modeling studies provide scientific support to the analysis of water resource problems and develop strategies for current and potential problems for the sustainable management of water resources. In this study, WEAP-PGM (Water Evaluation and Planning System—Plant Growth Model) was applied to the Sakarya River Basin in Turkey, where almost 50% of the area is agricultural land. The main goals in the study are compiling/integrating available data from different sources in a data-scarce region for hydrological models, and estimating the water budget components of Sakarya River Basin on an annual basis as well as investigating the applicability of WEAP-PGM. General model performance ratings indicated that model simulations represent streamflow variations at acceptable levels. Model results revealed that, runoff is 4747 million m3, flow to groundwater is 3065 million m3 and evapotranspiration is 23,011 million m3. This model setup can be used as a baseline for calculating the crop yields under climate change in the context of water-food-energy nexus in the further studies.