Water Budget Components Research Articles

Horizontal well hydraulics in leaky confined aquifer near a stream: analytical solutions for induced drawdown and water budget components.

Horizontal wells have gained popularity as a technology for exploring water resources and remediating aquifers over the last decades, due to costs and numerous technical benefits compared to traditional vertical wells. This study presents a set of analytical solutions for drawdown distribution and various components of water budget contributing to flow toward a horizontal well in an aquifer-aquitard system interacting with a fully penetrating stream. It is assumed that the water level in the upper unconfined aquifer remains fixed at a specific elevation during the course of the pumping in the lower leaky aquifer. The water budget components account for inflows from aquifer storage, stream depletion, and leakage across the aquifer-aquitard interface. Analytical solutions to this three-dimensional, transient, non-axisymmetric Darcian flow model are given for both transient and steady-state flow conditions, relying on a four-fold integral transform technique that includes a Robin-type boundary condition at the aquifer-aquitard interface. It is shown how various components of water budget collectively counterbalance the effect of pumping discharge, confirming that the mass is conserved under both continuous and non-continuous pumping scenarios. Response maps are prepared to assess how different components of water budget react to changes in the well position. Furthermore, it is found that the components of water budget are most sensitive to the well-to-stream distance and anisotropy ratio of the leaky aquifer.

Fire exclusion alters forest evapotranspiration: A comprehensive water budget analysis in longleaf pine woodlands

AbstractForests are critical to water resources, but high evapotranspiration (ET) can reduce water yield. Thinning and prescribed fire reduce forest density and often reduce ET, promoting higher water yield. However, results from such treatments have been inconsistent, possibly because of unknown interactions among individual ET components. We compare water budget components of longleaf pine (Pinus palustris Mill.) woodlands with frequent prescribed fire to the water budget components of fire‐excluded stands. We hypothesized that fire exclusion would result in higher ET due to increased midstory transpiration (Et) and interception (Ei), and higher evaporation from litter (Ilitter). Reference plots were burned every two years while treatment plots had fire excluded for 15–20 years. Fire treatments were repeated in two sites representing a soil moisture gradient, noted as mesic and xeric. We measured woody Et using sap flux, and we modeled groundcover Et using physiological models. We measured Ei of canopy and groundcover layers, modeled Es litter biomass, and constructed a total component‐based water budget for each site and treatment. Compared with reference plots, midstory Et was 300%–800% higher in fire exclusion plots. Groundcover Et was ~80% less than reference treatments, countering the effects of midstory growth on total ET. Stand Ei followed similar trends, with groundcover Ei in reference plots countering the effects of midstory and litter Ei in fire exclusion plots. As expected, total ET in the xeric site was 18% higher in fire exclusion plots. However, ET in the mesic site was 16% lower in the fire exclusion plots due to high groundcover Et and Ei in reference plots. Thus, our results show that fire exclusion changes total forest ET, but the size and direction of the effect vary depending on the balance between midstory and groundcover transpiration and interception. These results highlight the importance of groundcover in ecosystem function in low‐density forests and may help explain inconsistent results from studies of water yields following thinning and fire. While prescribed fire is a valuable tool in forest management, we suggest that the effects of fire on ET are complex and require careful accounting of all water fluxes within a forest ecosystem.

Challenges in applying water budget framework for estimating groundwater storage changes from GRACE observations

The application of a water budget framework to isolate Gravity Recovery and Climate Experiment (GRACE) groundwater storage anomalies (GRACE-GWA) from GRACE terrestrial water storage anomalies (GRACE-TWSA) is hindered by the lack of direct observations of water budget components. In GRACE groundwater studies, water budget components are frequently applied to isolate changes in a storage component from various auxiliary methods (e.g., land surface or hydrology models, reanalysis, or remote sensing) and are used as a supplement to, or a substitute for, in-situ measurements when direct observations are sparse or unavailable. The contribution of select auxiliary datasets to isolate GRACE-GWA from GRACE-TWSA is an enduring quandary, attributed to the various assumptions applied to resemble hydrologic processes in model formulations. This study systematically allocates water budget components from assorted auxiliary sources to demonstrate bias and distortion of GRACE-GWA resulting simply from water storage component data selection. Whereas previous GRACE-GWA studies used combinations of water budget component datasets with uncertainty derived from the variance of the combined water budget components, this study applies single estimates for each component to measure bias and variability. An initial comparative analysis focused on three basins with suitable in-situ groundwater observations and complex hydrology stores (e.g., large lakes and seasonal snow cover), with correlation coefficients ranging from 0.32 to 0.89. Our systematic analysis was extended to 12 additional basins that capture a range of hydrologic characteristics to highlight the inconsistency in GRACE-GWA estimates. The variability evident in GRACE-GWA estimates highlights that the selection of water budget components carries the risk of misleading outcomes when disaggregating GRACE-TWSA into GRACE-GWA. Our water budget intercomparison provides an important assessment of the limitation in extraction of GRACE-GWA, highlighting the usefulness of comprehensive appraisal of water budget components for GRACE groundwater studies.

Quantification of Nocturnal Water Use and Its Composition in a Eucalyptus urophylla × E. grandis Plantation on the Leizhou Peninsula, South China

AbstractNocturnal water use (Qnight) is an important component of the eucalyptus water budget, but it has always been under‐appreciated and poorly understood. To improve the accuracy of water balance estimates and the understanding of the nocturnal water use process in eucalypts plantations, we conducted a 3‐year study to investigate the characteristics of Qnight and its components in an E. urophylla × E. grandis plantation in southern China. The results showed that the Qnight of E. urophylla × E. grandis was substantial and the ratio of nocturnal to daily water use (Rnight) was on average 12.35%, with higher Rnight (14.97%) in the dry season than in the wet season (9.50%). The Qnight includes two components, nocturnal transpiration (Tn) and nocturnal refilling (Re), which are driven by different factors. Nocturnal Re‐Tn dynamics were controlled by a combination of nocturnal environmental factors that drive Tn and corresponding daytime environmental factors that drive daytime transpiration. Therefore, the compositional ratios of Tn and Re differed between weather conditions and months. We developed a novel method to distinguish between Re and Tn and quantified the dynamics of their ratios. We found that on a 3‐year average, the Qnight of E. urophylla × E. grandis was mainly used for Tn (58.63%). Our results highlight the non‐ignorability of Qnight and the high variability of the compositional ratios of Re and Tn, and suggest that Qnight and its components should be accurately quantified and considered when studying the water balance in eucalyptus stands.

Estimation of water budget and its components using Google Earth Engine approach

Accurate assessment of water budget components is crucial in many fields, such as agriculture, water resources management, hydrology, ecology, and climatology. In this study, a freely available web-based tool is developed using the Google Earth Engine (GEE) to evaluate the water budget components at various spatial and temporal scales.This study explores the effectiveness of the fifth generation of European ReAnalysis (ERA5) Land datasets processed bythe European Centre for Medium-Range Weather Forecasts (ECMWF). The water budget components such as precipitation, runoff, evapotranspiration, soil moisture, and storage change were analyzed monthly and annually at regional and river basin scales.The results showed that the water budget components were balanced at both spatial scales. Moreover, the result provided by this web-based tool was reasonable. Therefore, we are considering that this developed tool will help the farmers, watershed planners, and decision-makers to construct infrastructures and plan management activities at spatiotemporal scales.

Statistical downscaling of GRACE terrestrial water storage changes based on the Australian Water Outlook model

The coarse spatial resolution of the Gravity Recovery and Climate Experiment (GRACE) dataset has limited its application in local water resource management and accounting. Despite efforts to improve GRACE spatial resolution, achieving high resolution downscaled grids that correspond to local hydrological behaviour and patterns is still limited. To overcome this issue, we propose a novel statistical downscaling approach to improve the spatial resolution of GRACE-terrestrial water storage changes (ΔTWS) using precipitation, evapotranspiration (ET), and runoff data from the Australian Water Outlook. These water budget components drive changes in the GRACE water column in much of the global land area. Here, the GRACE dataset is downscaled from the original resolution of 1.0° × 1.0° to 0.05° × 0.05° over a large hydro-geologic basin in northern Australia (the Cambrian Limestone Aquifer—CLA), capturing sub- grid heterogeneity in ΔTWS of the region. The downscaled results are validated using data from 12 in-situ groundwater monitoring stations and water budget estimates of the CLA’s land water storage changes from April 2002 to June 2017. The change in water storage over time (ds/dt) estimated from the water budget model was weakly correlated (r = 0.34) with the downscaled GRACE ΔTWS. The weak relationship was attributed to the possible uncertainties inherent in the ET datasets used in the water budget, particularly during the summer months. Our proposed methodology provides an opportunity to improve freshwater reporting using GRACE and enhances the feasibility of downscaling efforts for other hydrological data to strengthen local-scale applications.

Incorporating Spatio-Temporal Changes of Well Irrigation into a Distributed Hydrologic Model to Improve Groundwater Anomaly Estimations for Basins with Expanding Agricultural Lands

This paper seeks to address the deficiency of utilizing satellite-based GRACE observations and model-based GLDAS water budget components in estimating the changes in the groundwater storage in Konya Endorheic Basin (KEB), a basin experiencing considerable land use land cover (LULC) change, primarily agricultural expansion. Cereal cultivation in the basin has a slight decreasing trend, however, the cultivation of crops with high water consumption, such as maize and sunflower, is increasing substantially. And total agricultural areas are increasing. GRACE-GLDAS approach does not accurately give the long-term groundwater decline in the basin, mainly because the land surface models employed in GLDAS cannot realistically simulate variations in water budget components as they do not consider the changes in LULC and do not possess an elaborated irrigation scheme. Here, we used a fully-distributed mesoscale hydrologic model, mHM, that can handle multiple LULC maps from different years. The model was modified to incorporate the spatio-temporal changes of agricultural fields in KEB and an explicit irrigation scheme since we hypothesized that the groundwater depletion is mainly caused by well irrigation. mHM was calibrated against streamflow observations for the period 2004–2019. The simulations show that the use of mHM with the incorporated features gives groundwater storage changes that are more consistent with the well-based observations than those obtained from the GRACE-GLDAS approach. On the other hand, the mHM simulation with a static LULC map, as in GLDAS models but with a better representation of irrigated fields, provides groundwater anomaly changes that are more consistent with the GRACE-GLDAS results, a further justification of insufficiency of the GLDAS-based approach in estimating groundwater variations for basins with considerable landscape change.

Validation of key Arctic energy and water budget components in CMIP6

We investigate historical simulations of relevant components of the Arctic energy and water budgets for 39 Coupled Model Intercomparison Project Phase 6 (CMIP6) models and validate them against observation-based estimates. We look at simulated seasonal cycles, long-term averages and trends of lateral transports and storage rates in atmosphere and ocean as well as vertical fluxes at top-of-atmosphere and the surface. We find large inter-model spreads and systematic biases in the representation of annual cycles and long-term averages. Surface freshwater fluxes associated with precipitation and evaporation as well as runoff from Arctic lands tend to be overestimated by most CMIP6 models and about two thirds of the analysed models feature an early timing bias of one month in the runoff cycle phase, related to an early snow melt bias and the lack of realistic river routing schemes. Further, large biases are found for oceanic volume transports, partly because data required for accurate oceanic transport computations has not been archived. Biases are also present in the simulated energy budget components. The net vertical energy flux out of the ocean at the Arctic surface as well as poleward oceanic heat transports are systematically underestimated by all models. We find strong anti-correlation between average oceanic heat transports and mean sea ice cover, atmospheric heat transports, and also the long-term ocean warming rate. The latter strongly suggests that accurate depiction of the mean state is a prerequisite for realistic projections of future warming of the Arctic. Our diagnostics also provide useful process-based metrics for model selection to constrain projections.

On understanding mountainous carbonate basins of the Mediterranean using parsimonious modeling solutions

Abstract. The study aims to demonstrate that an effective solution can be implemented for modeling complex carbonate basins, in the situation of limited data availability. Considering the alternative modeling approaches under circumstances of data shortage is more significant knowing the vulnerability and effectiveness of these kinds of basins to drought and climate change conditions. In this regard, a hybrid approach that combines time series analysis and reservoir modeling is proposed to describe behavior in carbonate basins. Time series analysis estimates the contributing area and response time of the fractured carbonate system beyond the catchment's hydrographic boundaries. The results obtained align with previous literature-based field surveys. This information is then used to develop a conceptual reservoir system using the GEOframe modeling system. The model is validated using in situ discharge observations and Earth observations (EO) data on evapotranspiration and snow. Model reliability is assessed using traditional goodness of fit indicators, hydrological signatures, and a novel statistical method based on empirical conditional probability. This approach enables detailed analysis and investigation of water budget components in Mediterranean carbonate catchments, highlighting their response to significant precipitation deficits. Overall, our results demonstrate that flows from carbonate rock areas outside the hydrographic boundaries significantly impact the water budget of the upper Nera River. The storage capacity of the carbonate basin plays a crucial role in sustaining river discharge during drought years. In a single dry year, meteorological drought is considerably attenuated, while in subsequent dry years, it is slightly intensified. Multi-year droughts result in slower recovery due to the time required for precipitation to replenish the depleted storage that supported river discharge in previous dry years. This unique behavior makes these basins particularly vulnerable to the more severe and frequent drought episodes expected under future climate change.

Average monthly recharge, surface runoff, and actual evapotranspiration estimation using WetSpass-M model in Low Folded Zone, Iraq

Abstract The evaluation of the spatial and temporal distribution of groundwater recharge is required to develop the regional groundwater model for more precise simulations of various management scenarios. WetSpass-M (Water and Energy Transfer between Soil, Plants, and Atmosphere under Steady-State Conditions), which is a GIS-based spatially distributed water balance model, is deployed to evaluate monthly groundwater recharge, surface runoff, and actual evapotranspiration in the Low Folded Zone from 2000 to 2019. ArcGIS software prepares the essential relevant input data for the Wetspass-M model as grid maps. They include monthly climatological measurements (precipitation, temperature, and wind speed), land cover distribution, soil map, groundwater depth, topography, and slope. The mean annual groundwater recharge, evapotranspiration, and runoff were found to be 128, 131, and 72 mm, respectively. Accordingly, recharge accounts for 39% of the precipitation, while the rest, 40 and 21%, become evapotranspiration and surface runoff, respectively. WetSpass-M model results are meant to enable integrated groundwater modeling. The study of simulation data demonstrates that the WetSpass-M model accurately simulates the hydrological water budget components of the Low Folded Zone. In addition, a better understanding of the simulated spatial and temporal distribution of water balance components is beneficial for managing and planning the available water resources of the Low Folded Zone in Iraq, which faces water scarcity threats.

A Decade of Data‐Driven Water Budgets: Synthesis and Bibliometric Review

AbstractScarce water resources across the globe have prompted the development of data‐driven water budgets to account for and distribute limited water more effectively across various land uses and purposes. Data‐driven approaches for estimating individual water budget components have been extensively developed and subsequently reviewed (e.g., evapotranspiration, precipitation, groundwater, surface water, runoff), but the state of the art of data‐driven approaches for estimating and integrating complete water budgets has not been the subject of a review paper to our knowledge. In this review, we fill this void by reviewing 81 systematically identified publications from the last decade (2012–2022) on data‐driven water budget approaches. We describe the current state of measurements and data products for data‐driven water budgets for various spatiotemporal scales. Our analysis suggests that spatiotemporal parameters drive the approach for data‐driven water budgets, with larger spatiotemporal scales relying more on satellite remote sensing data products and smaller spatiotemporal scales relying more on ground‐based monitoring. The incorporation of satellite remote sensing data products and ground‐based monitoring was common across various spatiotemporal scales and enabled the estimation of complete water budgets in areas of limited data availability. We conclude that improved reporting of simplifying assumptions, uncertainty analysis methods, and data sources are required for the alignment of water budget estimations between resource managers at varied spatiotemporal scales. Our review calls for the standardization of data‐driven water budget reporting protocols to improve the interpretability of data‐driven water budgets across decision‐makers working at various spatiotemporal scales.

Estimation of water budget components and its driving factors analysis in arid grassland

Clarifying the dependence of the grassland water budget change and its components on environmental factors is significant for the sustainable development of dryland ecosystems. Here, the Hydrus-1D model was used to simulate the water budget of natural grassland for 42 years (1980–2021). The standardized precipitation evapotranspiration index (SPEI) and soil moisture deficit index (SMDI) were used to analyze the soil drought evolution characteristics and the water use dynamic of the grassland in dry and wet years. Here, the calibrated Hydrus-1D model accurately identified the dynamic of grassland soil moisture in 2020 and 2021. The simulated data showed that evaporation (E) and transpiration (Tc) were the main pathways of soil water consumption, accounting for 96.5 % and 86.1 % of rainfall in dry and wet years, respectively. The soil water storage did not present a difference in precipitation proportion in dry (2.4 %) and wet (1.2 %) years, and the deep percolation accounted for a maximum of 12.8 % in wet years. Rainfall from 380 to 400 mm was the threshold, as it not only corresponds to the maximum water use efficiency (Tc/ET = 0.52, ET = E + Tc) but also serves as an important turning point for drought and deep percolation (below 150 cm) within the soil. The structural equation model further indicated that the dependence of E and Tc on meteorological factors was the main reason for the change of their proportions in dry and wet years. Tc was more sensitive to meteorological factors (R2 = 0.63), while E was not (R2 = 0.27). The SMDI had a greater impact on determining the threshold for water budget components than the SPEI. These results deepen the understanding of the hydrological process of grasslands in sandy areas, including the interaction between water budget components and environmental factors in wet and dry scenarios.

Numerical analysis of surface hydrogeological water budget to estimate unconfined aquifers recharge

Under changing climate, groundwater resources are the main drivers of socioeconomic development and ecosystem sustainability. This study assessed the contribution of two adjacent watersheds, Muse Street (MS) and West Wood (WW), with low and high urban development, to the Memphis aquifer recharge process in central Jackson, Tennessee, USA. The numerical MODFLOW model was created using data from 2017 to 2019 and calibrated using reported water budget components derived from in-situ data. The calibrated MODFLOW model was then used to investigate the impact of high and low urban developments on the recharge rate. The hydraulic parameters and recharge rates were optimized by adjusting the groundwater level based on the observed water level using PEST. The stochastic modeling was also carried out using the Latin Hypercube approach to reduce the uncertainty. The calibration results were satisfactory, with RMSE of 0.124 and 0.63 obtained in the WW and MS watersheds, respectively, indicating accurate estimation of the input parameters, precisely the hydrodynamic coefficients. The study results indicate that, per unit area, the MS watershed contributes 119% more to recharge and 186% more to riverbed leakage compared to the WW watershed. However, regarding total recharge and riverbed leakage, the WW watershed contributed more than the MS watershed. The results of this study have enhanced the knowledge of the impact of urbanization on hydrology and the recharge process in watersheds with diverse land uses.

Changes in the surface and atmospheric water budget due to projected Amazon deforestation: Lessons from a fully coupled model simulation

The Amazon forest has a complex interaction with climate at different spatial and temporal scales. This means that alterations in land use could modify the regional water cycle, including the surface and atmospheric water budget. However, little is known about how these changes occur seasonally and in a spatially distributed manner in the most vulnerable regions, such as the southern Amazon. In this study, the local to regional effects of future Amazon deforestation on the surface and atmospheric water budget components are investigated by twin numerical experiments using the Regional Earth System Model of the ‘Institute Pierre Simone Laplace’ (RegIPSL) for 19 yr (2001–2019). The results show that significant changes in precipitation and actual evapotranspiration in the southern Amazon (south of 5°S) are associated with surrounding areas with a deforested ratio higher than 40%. During the onset of the wet season (September-November) the largest changes in convective processes are manifested by opposite atmospheric dynamic in adjacent regions (dipole), associated with. This dynamic is associated with wind orientation and the different sizes of the straight corridors of continuous deforestation (pathways). The dipole manifests itself as a suppression of convection in the upwind sector, while convection increases in the downwind sector of the deforestation pathway. For medium-sized deforestation pathways (∼350 km) convection changes are related to dynamic processes (decrease in surface roughness). In large-sized pathways (∼500 km) the mechanisms causing convective changes are combined, dynamic and thermal (increase in surface temperature). In deforested regions there is an average increase of terrestrial water storage dynamics and runoff ∼10 times higher than in non-deforested regions. Furthermore, the atmosphere becomes ∼8 times drier in deforested regions than in non-deforested regions. Our findings indicate a new perspective regarding a comprehensive modeling approach to understand potential changes in the surface and atmospheric water cycle in different regions of Amazonia and in different seasons due to future deforestation and thus provide new insights into their spatial and temporal variability at sub-regional scales.

Evaluation of the storage and evapotranspiration terms of the water budget for an agricultural watershed using local and remote-sensing measurements

The understanding of the water budget components, especially evapotranspiration and the amount of water stored in the watershed, is key to water resources management and hydrological modeling in general. In this work, we present the analysis of 13 hydrological years’ measurements of discharge, precipitation, evapotranspiration, and soil moisture over two agricultural watersheds in Eastern Nebraska, United States. These data were used to investigate several facets of the hydrological water budget: water- and energy-balance closures, water budget residues (here, the water budget residue is the remaining imbalance after all water budget terms have been considered; see Eq. (13)), storage in the unsaturated and saturated soil layers, and the evapotranspiration derived from the water budget. Remote-sensing data were also used to assess the spatial variability of net radiation and soil moisture over the basins. Adjusting the eddy-covariance measured evapotranspiration to close the energy budget agreed, in the long term, with the water budget evapotranspiration estimates. The evapotranspiration estimated with storage calculated with soil moisture measurements and recession analysis presented the best agreement with the (adjusted) measured evapotranspiration, but considering only either the vadose zone or the saturated zone for storage estimates still produced reasonable results. We found considerable variability in soil moisture over the basins in the final period of the growing season, coinciding with the time of the year when water budget residues were largest.

Evaluation of BOLAM Fine Grid Weather Forecasts with Emphasis on Hydrological Applications

The evaluation of weather forecast accuracy is of major interest in decision making in almost every sector of the economy and in civil protection. To this, a detailed assessment of Bologna Limited-Area Model (BOLAM) seven days fine grid 3 h predictions is made for precipitation, air temperature, relative humidity, and wind speed over a large lowland agricultural area of a Mediterranean-type climate, characterized by hot summers and rainy moderate winters (plain of Arta, NW Greece). Timeseries that cover a four-year period (2016–2019) from seven agro-meteorological stations located at the study area are used to run a range of contingency and accuracy measures as well as Taylor diagrams, and the results are thoroughly discussed. The overall results showed that the model failed to comply with the precipitation regime throughout the study area, while the results were mediocre for wind speed. Considering relative humidity, the results revealed acceptable performance and good correlation between the model output and the observed values, for the early days of forecast. Only in air temperature, the forecasts exhibited very good performance. Discussion is made on the ability of the model to predict major rainfall events and to estimate water budget components as rainfall and reference evapotranspiration. The need for skilled weather forecasts from improved versions of the examined model that may incorporate post-processing techniques to improve predictions or from other forecasting services is underlined.

An analysis of terrestrial water storage changes of a karstic, endorheic basin in central Anatolia, Turkey

Water budget components of endorheic basins of semi-arid and karstic characters are difficult to assess. In this study, we attempt to estimate the water budget components of the Konya Endorheic Basin (KEB), which is a semi-arid, karstic basin in central Anatolia, using The Gravity Recovery and Climate Experiment mission (GRACE) observations and Global Land Data Assimilation System (GLDAS) data over the period 2002-2019. We also investigate the trends and sub-trends in the time series of the hydrometeorological parameters. The results indicate that the available water potential in the basin has a decreasing trend over the study period. Precipitation and evapotranspiration show increasing trends in the basin, however, the other hydrometeorological parameters demonstrate decreasing trends. Both Terrestrial Water Storage Anomaly (TWSA) and groundwater level decrease significantly (20.21 mm/yr and 122.34 mm/yr, respectively). The dry 2008 and subsequent wet year created a hydrological breaking point in the time series. The weights of soil moisture and groundwater storages are relatively large amongst the TWSA components (49.61% and 33.12%, respectively). The surface water storage anomaly comes at the third place with a 14% weight. It is assessed that the groundwater storage system responds to precipitation with a delay of 6 months. Limestone zones respond more sharply to groundwater depletion than alluvial zones. It should be noted that the GRACE and GLDAS data could be used together to successfully estimate the water budget components for sustainable management of the limited water resources of the basin.

Comparative Analysis of Global Terrestrial Water Storage Simulations: Assessing CABLE, Noah-MP, PCR-GLOBWB, and GLDAS Performances during the GRACE and GRACE-FO Era

Hydrology and land surface and models (HM and LSM) are essential tools for estimating global terrestrial water storage (TWS), an important component of the global water budget for assessing the accessibility and long-term variability of water supplies. With the expansion of open-source and open-data policies, the community can now perform model TWS simulation from source codes as well as directly exploit end-user hydrologic products for water resource applications. Regardless of the model effectiveness and usability, an accuracy assessment is necessary to quantify the model’s global and regional strengths, weaknesses, and reliability. This paper compares the most recent global TWS estimates from six models, namely the PCRaster Global Water Balance (PCR-GLOBWB), Noah, Noah-Multiparameterization (Noah-MP), Catchment LSM, and Variable Infiltration Capacity (VIC), and Community Atmosphere Biosphere Land Exchange (CABLE)—the latter of which is cross validated for the first time. TWS observations from the Gravity Recovery And Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) satellite missions between 2002 and 2021 are used to validate the model. The analyses show that Noah-MP outperforms other models in terms of global average correlations and root mean square errors. PCR-GLOBWB performance is superior in irrigated regions because of the inclusion of human intervention components in the model. CABLE, a core LSM of the Australian climate model, significantly outperforms all others in Australia. CLSM performs reasonably well, but the TWS long-term trend appears to be incorrect due to an overestimated groundwater component. Noah performs similarly (but inferiorly) to Noah-MP, most likely due to model physics sharing. VIC has the least agreement with GRACE and GRACE-FO. The evaluation also sheds some light on the role of forcing data in model performance, particularly for ready-to-use products such as GLDAS, where incorporating MERRA-2 or ERA5 data into GLDAS Noah simulations may potentially improve its TWS accuracy, which has previously been overlooked due to limited modeling capacity. Despite each model’s unique strength, the ensemble mean TWS, particularly when Noah-MP and PCR-GLOBWB are included, yields better TWS estimates than an individual model result. The findings of this study could serve as a benchmark for future model development and the data published in this paper could aid in the scientific advancement and discoveries of the hydrology community.

Understanding the dynamics of evaporation from stony soils via laboratory experiments and numerical modeling

Stones and rock fragments are typically found within soil profiles across various landscapes. However, knowledge on, and understanding of, their impact on hydraulic functions and processes are still lacking. Specifically, the presence of stones within the soil profile may increase water storage and availability to vegetation and reduce plant mortality in drylands. However, physically-based testing of stones effect on soil water budget components is overlooked. Experiments under laboratory conditions from soil columns, with two volume content t levels and two sizes of stones, were carried out in this research. Our results reveal that stoniness reduces the duration of stage-1 evaporation (S1) and consequently the overall cumulative evaporation, proportionally to their volumetric content and to the initial soil water content. The effect of stone size on evaporation was minor during S1 but was more pronounced during stage-2 (S2) — when the evaporation front migrates downward — with smaller stones reducing evaporation more than the larger ones. A recent evaporation model, assuming that transient evaporation is a succession of steady state solutions, was applied to explain the 2-phases evaporation process in a stony profile. The model results indicate that apart from changing the effective porosity of the soil profile by replacing a soil volume by stones, stoniness affects mainly the hydraulic conductivity function but practically not the water retention curve. Stoniness induced an increase in the tortuosity-related parameters compared with those of the stone-free soil. This observation was strengthened by the fact that both measured and modelled data reveal that stoniness has not affected the downward movement of the water table level during drying. Although we tested two stone sizes only and further experiments are required for a broader understanding, we suggest that the outcoming insights may improve estimates of water budget components in stony soil profiles and their response to global climatic changes.

Water and energy budgets over hydrological basins on short and long timescales

Abstract. Quantifying regional water and energy fluxes much more accurately from observations is essential for assessing the capability of climate and Earth system models and their ability to simulate future change. This study uses satellite observations to produce monthly flux estimates for each component of the terrestrial water and energy budget over selected large river basins from 2002 to 2013. Prior to optimisation, the water budget residuals vary between 1.5 % and 35 % precipitation by basin, and the magnitude of the imbalance between the net radiation and the corresponding turbulent heat fluxes ranges between 1 and 12 W m−2 in the long-term average. In order to further assess these imbalances, a flux-inferred surface storage (Sfi) is used for both water and energy, based on integrating the flux observations. This exposes mismatches in seasonal water storage in addition to important inter-annual variability between GRACE (Gravity Recovery and Climate Experiment) and the storage suggested by the other flux observations. Our optimisation ensures that the flux estimates are consistent with the total water storage changes from GRACE on short (monthly) and longer timescales, while also balancing a coupled long-term energy budget by using a sequential approach. All the flux adjustments made during the optimisation are small and within uncertainty estimates, using a χ2 test, and inter-annual variability from observations is retained. The optimisation also reduces formal uncertainties for individual flux components. When compared with results from the previous literature in basins such as the Mississippi, Congo, and Huang He rivers, our results show better agreement with GRACE variability and trends in each case.