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Water balance quantifies the inflows and outflows in a river basin, crucial for assessing the water resources of a given area. Quantified water balance should therefore be the key step in environmental quality assessment. However, due to the lack of data on reasonable spatiotemporal scales and quality, water balance studies are scarce. The aim of the paper was to provide a water balance analysis as a prerequisite for aquatic and wetland ecosystems management in the Biebrza Valley, Poland. A Penck-Oppokov method was used to assess the annual water balance, and runoff coefficient for 1951–2021. Data were extracted for the daily simulated dataset of Poland. The average annual water balance of the Biebrza basin encompassed of 561 mm of precipitation, 485 mm of evapotranspiration, 101 mm of runoff, and −25 mm of water retention. Analysis of 17 sub-basins indicated a declining tendency in water resources over the study period. The average runoff coefficient in the Biebrza basins is equal to 0.17. Findings presented here indicate that the significant deficit in the water balance in the region is highly unlikely to be compensated by the course of natural hydrological processes. This reveals the need for quick actions oriented at improvement of water balance by reducing the runoff and evapotranspiration. The study provides convincing evidence that if the observed tendencies of water balance elements are continued, the reinstallation of spatially distributed, abundant measures of increasing water retention may be the only way to assure the appropriate ecological status of aquatic and wetland ecosystems. [ABSTRACT FROM AUTHOR]

• GRACE observations and GLDAS data are used to obtain total water storage (TWS) components for an endorheic basin in central Turkey. • Contrary to expectation, the impact of soil moisture on TWS anomaly is found to be larger than that of groundwater. • TWS anomaly time series indicate a significant decline, implying that the basin is losing more water than it is gaining. • The groundwater storage system of the basin responds to precipitation in a relatively short time period (6 months). 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. [ABSTRACT FROM AUTHOR]

Egypt's water resources face challenges arising from escalating urban demand, changes in land use, environmental requirements, and the impacts of climate change. To address these challenges, the study develops a dynamic model using WEAP model as a decision support tool for water sector planning and management. By comparing different scenarios, the research examines the benefits of water conservation in terms of cost reduction in supply, wastewater generation, and treatment. Considering the projection period until 2037, it is imperative to carefully examine the research findings and explore opportunities for further optimizing water use efficiency. Based on the model simulation results, it is anticipated that the total water demands in Egypt will rise from 78.40 billion cubic meters (BCM) in 2023 (comprising 61.10 BCM for the agricultural sector, 12.58 BCM for the municipal sector, and 5.73 BCM for the industrial sector) to 81.02 BCM in 2037. The water demand for the agricultural sector is projected to decrease from 61.30 billion cubic meters (BCM) in 2023 to 60.14 BCM in 2037 as a result of the implementation of modern and smart irrigation systems. Conversely, the municipal sector is expected to experience an increase from 12.58 BCM in 2023 to 14.88 BCM in 2037. Furthermore, for the industrial sector, the water demand is anticipated to rise from 5.73 BCM in 2023 to 6.00 BCM in 2037. [ABSTRACT FROM AUTHOR]

Terracing engineering and vegetation plantation have been implemented in many water-limited areas, aiming to reduce the effect of drought, conserve water, and promote ecosystem restoration. However, due to the complexities of slope structure, the major hydrologic processes controlling the water balance of terraces are still unclear. To further quantify the role of terraces on water retention in the stand scale, in a normal year (2015) and a dry year (2016), we compared the water balance for the combination of Platycladus orientalis with zig terrace (PZ), fish scale pits (PF), and natural slope (PN) in a typical loess hilly area of China. Our results indicated that terracing was an effective way to increase water retention and reduce runoff. After the growing season, compared with PN, terraced fields enhanced the water budget with 13.6–21.3 mm for PZ and 2.4–11.7 mm for PF. In addition, terraced fields generated less runoff (a reduction of 45.3–60.8 % for PZ and 19.6–26.6 % for PF) and more soil water storage (an increase of 18.5–24.1 % for PZ and 13.6–14.7 % for PF) than the natural slope. Overall, the water budget of all plots was positive (29.6 mm for PZ > 20.0 mm for PF > 8.3 mm for PN) in the normal year (2015) and negative (−49.6 mm for PZ > −60.8 mm for PF > −63.2 mm for PN) in the dry year (2016). Our results suggest that precipitation is still the primary factor affecting the water budget in woodlands, and terracing measures can help to improve the utilization of precipitation and enhance soil water retention in the Loess Plateau. [ABSTRACT FROM AUTHOR]

• Water table fluctuation method analyzed through comparison to analytically based recharge. • The water table fluctuation method mostly under-estimates recharge. • Current approaches to the extrapolation of the antecedent recession curve need to be revised. Distributed recharge is commonly predicted from groundwater level data by adopting the water table fluctuation method (WTFM). The simplicity of the technique makes it attractive for groundwater management applications seeking sustainable levels of extraction. While there are variations to the WTFM, the classic approach extends the antecedent recession curve (prior to recharge events) to allow for the estimation of the gross recharge. This is achieved using either the previous (local) recession or a master recession curve obtained from multiple recession events. The most common function used for the recession extension is exponential. Despite the wide application of the WTFM, remarkably, a validation of this approach against known recharge values has not been previously attempted. This is the goal of the current study, which also compares local recession and master recession curve approaches adopting an exponential function for estimating recharge using the WTFM. Stochastic analysis applying an existing analytical solution to water table fluctuations from intermittent recharge was used to produce 1000 hypothetical hydrographs. From these, WTFM-based recharge was estimated for three recession periods of differing lengths, producing 6000 estimates of recharge (1000 simulations, two recession curve approaches, three recharge-recession events). The WTFM produced an average under-estimation error of 14%. The WTFM is more likely to obtain recharge errors within 5% of the true value using the master recession curve approach. This study demonstrates the need to revise the WTFM to eliminate bias, especially in the extrapolation of antecedent recession curves. [ABSTRACT FROM AUTHOR]

[Display omitted] • An exact and low-impact means for ecohydrological survey in wetlands is verified. • Onsite tests for water interaction and exchanges prove the process effectiveness. • Water balance model indicates the groundwater losses and management implications. • The powerful tools suggest to replace conventional methods in habitat ecohydrology. Comprehending the hydrological conditions in wetlands is a critical aspect of successfully enhancing wetland conservation. The interaction between wetland surface water and groundwater is a complex process, requiring detailed onsite hydrological and soil surveys, laboratory experiments, and modeling to clarify this relationship. However, conventional investigation methods often cause significant disruptions and thus may affect the natural environment and compromise data reliability. In this study, a high-accuracy and low-environmental-disturbance (LED) approach was proposed involving modified falling head permeability and modified seepage meter tests to elucidate the groundwater characteristics in an ecological reserve. A water balance (WB) calculation method was employed to examine the performance of the proposed LED approach. The results revealed that the LED performed better than conventional methods in hydraulic conductivity and seepage velocity exploration, thereby improving the accuracy of quantifying groundwater flow. Moreover, the experimental findings and ecohydrological observations were used to assess the groundwater flow regime, and the data were consistent with the field survey results. The contradiction between conducting research and protecting ecological reserves can pose difficulties in the sustainable and effective management of wetlands. The LED approach can be applied broadly, especially in areas where significant disturbance should be avoided. The water budget model can thus be developed to help deduce the interaction between groundwater and surface water. We suggest that these innovative methods are effective tools and can assist both scientists and authorities in formulating corresponding habitat management strategies. [ABSTRACT FROM AUTHOR]

Remote sensing-based surface energy balance algorithms have been used to estimate water use of various crops. However, citrus evapotranspiration (ET) estimation is challenging mainly due to evergreen leaves and a clumped canopy structure. In this study, we evaluated the performance of two methods for calculating ET: the ensemble of OpenET models, which are mostly satellite thermal-based models, and the BAITSSS water and energy balance model. Calculated ET was compared with (i.) eddy covariance (EC) ET measurements and (ii.) water received (irrigation plus precipitation) data for two citrus orchards in San Joaquin Valley, California. Polaris-based soil hydraulic properties and measured volumetric water content were used for BAITSSS parameterization and initialization, respectively. Sentinel-2 based NDVI was used for BAITSSS simulation. Results showed that annual ET based on the OpenET ensemble model (1169 mm) was on average 30 % larger (r2 ∼ 0.71, RMSE ∼ 1.16 mm) than both EC ET (908 mm) and water received (886 mm). The disparity mostly occurred in spring. BAITSSS, on the other hand, showed mixed results compared to observations (r2 ∼ 0.77, RMSE ∼ 0.94 mm). Both measured from EC and modeled ET from BAITSSS and ensemble OpenET values were below grass reference ET (ET o) for the majority of the simulation period. Soil moisture and water received data indicated the orchards may have been deficit irrigated. Overall, this study highlights the challenges of ET modeling in citrus orchards and the need for improved estimation of ET for this specialty crop. • Citrus evapotranspiration estimation is challenging mainly due to evergreen leaves and a clumped canopy structure. • OpenET ensemble model was on average 30 % larger than eddy covariance and water received. • Disparity was mostly due to disagreements during spring. [ABSTRACT FROM AUTHOR]

Giant reed (Arundo donax L.), a woody grass native to the Mediterranean, has become a cause of concern for national water security in its invaded range of the arid southwestern United States, Australia, New Zealand, and South Africa. The main objective of this study was to provide the first, landscape-level estimates of water use by giant reed. The study utilized the eddy covariance method to quantify evapotranspiration (ET) throughout the 2014 and 2015 growing seasons along the Rio Grande River in Eagle Pass, Texas. We monitored ET concurrently with the implementation of a biological control program targeting giant reed. Daily ET rates were strongly associated with the phenology of giant reed, as estimated by degree day accumulation. Monthly ET was higher in each month of the active growing season (May–October) of giant reed in 2014 than in 2015. Consequently, seasonal (DOY 121-304) ET was substantially higher in 2014 (842 mm) than in 2015 (625 mm) even though the 2015 growing season was wetter. Cumulative rainfall from May to October was 188 and 264 mm in 2014 and 2015, respectively. Our study indicated that the reduction in ET could be attributed to the presence of specialist insect biological control agent, the stem-galling arundo wasp (Tetramesa romana). In 2015, we observed a 28.6% (May), 53.5% (June), and 44% (July) increase in the number of arundo wasps captured in sticky traps from the previous year. Additional studies are needed to quantify conservation and economic benefits of the biological control program in the Rio Grande Basin. [ABSTRACT FROM AUTHOR]

Paleoclimate proxy studies of wetland sediment cores often document the direction if not the magnitude of climate change because transfer functions (pollen, diatoms, etc.) are unavailable or imprecise. A water-budget approach, presented here, circumvents the need for transfer functions in wetlands, using the Garden Basin cattail fen (GBC; Fish Lake Plateau, Utah, USA) as a model system. Prior studies of the GBC fen revealed both high and low-frequency oscillations between fen and pond states over the last 12.5 ka. Pollen indicated that pond-like conditions were accompanied by both greater monsoon and annual precipitation rates. However, the magnitude of these changes was not estimated. By synthesizing multiple approaches, including water-level monitoring, remote sensing (normalized difference vegetation index, NDVI), and terrain analysis, limits were placed on precipitation changes required for pond versus fen ecosystems in Garden Basin. NDVI data show that water levels may be controlled by evapotranspiration (ET) instead of spring snowmelt. Water levels increase in mid-winter in response to the decline of photosynthesis of surrounding piñon-juniper (PJ) forest. In late summer through fall, ET drives the fen system into a moisture deficit and water declines below the ground surface. Quantitative limits on both annual and seasonal precipitation changes can be obtained through water budgets. For the GBC model, mean annual precipitation (~350 mm/yr) must double (~700 mm/yr) to sustain perennial standing water for 95% of years. Increases in late summer (monsoon) through fall (cyclonic) precipitation requires lesser rates (100–200 mm/yr) to satisfy PJ ET demands to maintain standing water. Thus, the habitats of many wetlands globally may be particularly sensitive to late-season precipitation where ET is the primary control on water levels. In summary, the GBC fen and its water budget are a template for quantifying the magnitude, rather than just the direction, of precipitation change in wetland systems through time. [ABSTRACT FROM AUTHOR]

During groundwater pumping from unconfined aquifers, evapotranspiration can be reduced as the water table drops, a process known as salvage. This phenomenon must be included in water balance assessments for accurate predictions of groundwater withdrawals. Although the salvage phenomenon has been well understood for a long time, i.e., since Theis' pioneering studies, the models that were later developed by Bredehoeft always relied on numerical techniques to treat the inherent non-linearity, most commonly using MODFLOW. Analytical methods have been previously used with success for practical evaluation of water balance components such as stream depletion rates. This work presents a novel analytical solution of the Bredehoeft problem. It is a breakthrough in analytical evaluation of transient salvage losses induced by groundwater withdrawals due to declines of water table. We evaluate stream depletion and loss of storage in addition to salvage, using the new model. Detailed analysis of the solution using COMSOL software indicates that the linear approximation used in the analytical solution is accurate for most practical cases. Diagrams for drawdown, water balance and evaluation of solution accuracy are presented, considering a broad range of problem parameters. Results can be used for analyses of watershed-scale water balances. • A novel analytical solution of salvage rate for pumping near a stream is derived. • Solution implements an approximation of linearized evapotranspiration term. • Solution is compared to numerical results using COMSOL. • Solution is found to be accurate for a wide range of physical parameters. • Results can be used for analyses of watershed-scale water balances. [ABSTRACT FROM AUTHOR]

The formerly perennial Katuma River in western Tanzania starts in a protected forest, it then flows through irrigated rice farms before reaching Lake Katavi, a floodplain wetland whose outflow regulates the river flow through the Katavi National Park (KNP) down to its outlet at Lake Rukwa, which has no outlet. In recent years, due to overexploitation of water for irrigation, the Katuma River dried out for up to four months per year and this greatly degraded the KNP ecosystem, the siltation of river lead to flooding of the adjacent areas during heavy rains, and the water level of Lake Rukwa has decreased by 4 m since 1992 while its fishery yield and water quality also deteriorated. In 2016, a total of 46 illegal weirs were removed from the Katuma River upstream of KNP. Following that, the river zero-flow periods were reduced by two months and Lake Rukwa water level rose by 1 m. We suggest that the construction of a low V-notch weir at the outlet of the Lake Katavi wetlands would further reduce the Katuma River zero-flow periods by an additional month, thus returning the river nearly to its former perennial status. The enforcement of regulations governing the construction of irrigation weirs is essential. These ecohydrology solutions do not eliminate the threats, but they amplify the opportunities for sustainable development at the basin scale. This example of active governance of water resources at the basin scale can be applied throughout Tanzania and in semi-arid East Africa in general. [ABSTRACT FROM AUTHOR]

North Cyprus has been experiencing water scarcity since 1960 due to the limited freshwater resources, climate impact, and high rate of evaporation. As there are no perennial rivers, the island is largely dependent on groundwater as the main source of supply. The gradual increase in water demand led to the excessive extraction of freshwater from aquifers; this caused seawater intrusion, thus making the scarcity more alarming. Hence, this research was conducted to provide an update on the trend of the water budget of the country. Data were collected between 2000 to 2012 from the relevant authorities and used to achieve the study objective. Statistical relationships and the Blaney-Criddle method were applied to process the data. It was found that domestic water demands increased from 35.9 to 50.4 MCM while conveyance losses declined from 55.8 to 24.2 MCM. Moreover, an assessment conducted for the agricultural economy of 21 groups of crops showed that about 146.7 and 115.1 million USD were generated in 2011 and 2012, respectively. The overall results implied that the trend of water demand for agricultural production fluctuates with time and the general trend of water use is negative owing to the modernization of irrigation systems that minimizes the losses. [ABSTRACT FROM AUTHOR]

In New Zealand, dairy farming faces increasing scrutiny for its environmental impacts, including those on soil carbon (C) stocks; hence, alternative management practices are required. One such practice is usage of deep-rooting forage, such as lucerne (Medicago sativa L.). We measured the C and water exchange of two neighbouring lucerne fields on stony, well-drained soil for 3 years, following conversion from grassland. One field received irrigation and effluent; the other received neither. Net CO 2 exchange and evaporation were measured by eddy covariance, drainage and leaching with lysimeters, and water inputs with rain gauges. Biomass removal from harvesting and grazing was recorded by direct sampling. In the conversion year, irrigated lucerne was C-neutral despite two harvests and losses from the conversion process. In the 2nd and 3rd years combined, the biomass-C removal exceeded net CO 2 uptake, causing net losses of 450 g C m−2 and 210 g C m−2 for irrigated and non-irrigated lucerne, respectively. Leaching losses accounted for 1 to 9 % of annual net C uptake from the atmosphere. The ratio of ecosystem respiration to gross photosynthetic productivity (GPP) increased from <0.7 in spring to ≈ 1 in autumn. Consequently, the net C balance for both lucerne crops showed gains in the first two growth periods of each year and losses in the subsequent two to four growth periods. Irrigation made no difference to the photosynthetic water-use efficiency at field scale (GPP/evaporation), but enhanced production water-use efficiency (biomass/water input). Irrigation increased both the absolute amount of drainage and the fraction of water inputs lost by drainage. In one year, significant summer drainage occurred for the irrigated lucerne. To prevent that, soil-water content should be kept well below field capacity but above the crop's water-stress level. Such practice would likely also help retain soil carbon. Annual cumulative carbon budgets of lucerne on stony soil. Unlabelled Image • Net imports and exports of carbon and water for lucerne on stony soils were measured. • Irrigated lucerne had a near-neutral net ecosystem C budget in the conversion year. • In following 2 years, both irrigated and non-irrigated lucerne showed net C losses. • Irrigation increased production, biomass removal, net C loss and drainage. • Water-use efficiency was similar for irrigated and non-irrigated lucerne. [ABSTRACT FROM AUTHOR]

• Regional climate of upper Mesopotamia was simulated with different land use maps. • Land use maps were produced to include the agricultural expansion in the region. • Enlargement of irrigated crop areas is changing the water budget of the region. • Water loss through evapotranspiration increases significantly, amplifying water deficit. • Water surplus of headwaters won't likely meet downstream water deficit in the future. The waters of the Euphrates and Tigris rivers have always been a vital resource in the water-food-energy nexus of the Middle East region. The currently ongoing Southeastern Anatolia Project (GAP) in Turkey aims to increase regional prosperity by optimizing the use of these waters for irrigation and hydropower. Since the beginning of the 1990s, the irrigation schemes and water management infrastructures within the scope of the GAP have caused significant land use and land cover (LULC) change in this semi-arid region. We employed a high resolution regional climate model to simulate the effects of irrigation induced LULC changes on the regional water and energy balances. For this purpose, historical simulations were conducted by using three land cover distributions which reflect the increase in irrigation and water surfaces. Our experiment reveals that water loss through evapotranspiration increases significantly with the areal expansion of irrigation. This increase is driven by the change in partitioning of the available energy at the surface between turbulent heat fluxes. On the one hand, a significant reduction in sensible heat flux causes local cooling by around 0.4 °C and 0.8 °C for the current and future irrigation conditions, respectively. On the other hand, the increase in latent heat flux enhances evapotranspiration and consequently atmospheric water vapor concentration. The moistening of a shallower boundary layer triggers the formation of convective clouds, which increases convective precipitation, most notably during the irrigation months. The enhanced water loss through evapotranspiration has potential to significantly alter the water budget of the GAP region. It seems that the water surplus of the headwaters region may not be enough to meet the water deficit of the GAP region in the future if the planned irrigation schemes are carried out to completion. [ABSTRACT FROM AUTHOR]

• Multi-method approach for attributing hydrological changes in the Alpine region. • Shifts in precipitation patterns cause streamflow alterations in the Adige River Basin. • Climate change manifests itself in many facets depending on catchment spatial scale. The Alpine region is a particularly sensitive environment rich in water resources nurturing delicate freshwater ecosystems, which are however threatened by intensive exploitation for hydropower production and irrigated agriculture. The impact of water uses on the hydrological cycle is intimately intertwined with changes of the climatic forcing, which operate over a wide range of temporal and spatial scales. In the present study historical time series of streamflow, precipitation and temperature, recorded in the Adige River Basin, a large Alpine watershed in northeastern Italy, are analyzed in order to quantify alterations of the main hydrological fluxes due to changes in climate and water uses. Spatial and temporal patterns of change are detected by comparing annual and seasonal components of the water budget performed in four representative sub-catchments (with size ranging from 207 to 9,852 km2) characterized by different climatic and water use conditions. Afterwards, a multi-method approach is applied for attributing the observed changes to their main drivers. Summer streamflow depletion affects the Adige lowlands since the '70s, which is attributed to both the reduction of winter precipitation and the development of irrigated agriculture. Conversely, winter streamflow increased in headwater catchments due to the increase of aquifers recharge in autumn, which is consistent with the increase of precipitation in the same period. These results reveal that the impact of climate change on the Adige Basin is multifaceted, scale-dependent and intertwined with the effects of changes in water resources exploitation. [ABSTRACT FROM AUTHOR]

• Groundwater storage oscillated with precipitation-evapotranspiration difference. • Climate change and gullies had a hysteresis effect on groundwater storage change. • Horizontal movement dominated groundwater exchanges. • Deep gullies enhanced horizontal groundwater seepage. • Greater groundwater volume losses via deep gullies over long-term climate change. Climate change and gullies (and ditches) on peatlands are well known factors altering peat hydrology. Yet, exactly how this alteration emerges from interaction of these factors with groundwater dynamics is still not fully understood. In this study, we tackled this issue by coupling field measurement with model simulation using Visual MODFLOW. Groundwater processes and the associated water budget during five months of the wet season, 2017 were examined in the Zoige peatland, located on the northeastern side of Qinghai-Tibet Plateau, China with elevations of 3400–3900 m. Simulations were performed for a peatland area of 3.89 × 104 m2 and three sub-zones within it representing peatland with no gullies (NG), a deep gully cutting through the peat layer (CT), and a shallow gully whose bed is within the peat layer (NCT). Model input parameters were calibrated and validated using the field-measured data. Modeling outcomes led to water budget showing relative contributions of main hydrological pathways (MHPs) (i.e., precipitation (P), evapotranspiration (ET), gully, groundwater flow, and boundary) to changes of water storage in peats (Δ S). Although these MHPs varied differently during rain and inter-rain periods, Δ S values were mainly controlled by the oscillated trend of the difference between P and ET. Variations of MHPs caused by NCT and CT were secondary to those due to those of P and ET during the wet season referred to as the short-term climate change. Vertical groundwater (VGW) flows were strongly correlated with water table (WT) levels in both rain and inter-rain periods, but their directions had different patterns in the two periods. Horizontal groundwater (HGW) flows tended to move into the deep (CT) gully, while move from the shallow (NCT) gully to the neighbor peats during both periods. Since HGW flows were about ten times greater than VGW ones, their effect on Δ S was significant during the long dry season. This would lead to continuous loss of groundwater stored in peats, demonstrating the coupled effect of long-term climate change and gullies on Δ S. These findings underline the necessity of controlling gully development and avoiding ditch excavation in future Zoige peatland management practices. [ABSTRACT FROM AUTHOR]

• Literature-based and alternative equations for quick-flow runoff are tested. • A new empirical equation was found to outperform previously used equations. • Monthly maps of quick-flow runoff are produced and evaluated for the CONUS. • Patterns of increased quick-flow runoff in winter-spring months are observed. The quantitative estimation of the quick-flow runoff component of streamflow is required for many hydrologic applications. Estimation at the monthly timescale and national spatial scale would be particularly useful for national water availability modeling. This paper reviews a sample of commonly used equations for quick-flow runoff, including several currently in use in continental-scale models. The review shows the wide range of equation forms or heuristics currently in use to predict quick-flow runoff, the limited spatial scale over which these equations are often developed or calibrated, and the scarcity of well-tested equations available for quick-flow runoff at the monthly timescale. Data were gathered from a set of 1301 gaged watersheds across the United States to test a range of equations from the literature, along with several alternative equations, to assess and compare their performance in predicting quick-flow runoff at the monthly timescale. The highest-performing equation was selected for application to monthly maps of explanatory variables to produce monthly quick-flow runoff water budget contribution maps. This equation is a regression against precipitation, soil saturated hydraulic conductivity, surficial geology type, and slope data. Its application indicates that average quick-flow runoff across the conterminous United States in the winter exceeds that in the summer by up to a factor of three. The monthly maps were explored and evaluated for the timespan of 2000–2015. The comparison of equation forms and produced monthly maps will be useful for a variety of hydrologic modeling and monitoring applications. [ABSTRACT FROM AUTHOR]

Highlights • We outline a water-energy balance approach for multi-scalar and multi-category drought analysis. • The proposed approach is able to capture meteorological, hydrological, and agricultural droughts. • The new drought index outperforms previous drought indices (SPEI and scPDSI), especially in non-humid regions. Abstract Different categories of droughts (e.g., meteorological, agricultural, hydrological), and their multi-scalar features often make description of drought onset, persistence, and termination challenging and often subjective. Here we show that a water-energy balance based indicator, named Standardized Moisture Anomaly Index (SZI), better captures multiple categories of droughts and their multi-scalar features. We globally evaluate and compare the performance of SZI with existing drought indicators that use potential evapotranspiration (PET) as a measure of atmospheric water demand including the Standardized Precipitation Evapotranspiration Index (SPEI) and self-calibrated Palmer Drought Severity Index (scPDSI). We show that while PET is a good indicator for characterizing the climate aridity, using it as a measure of atmospheric water demand for drought analysis leads to misrepresentation of droughts, especially over water-limited (non-humid) regions where the actual evapotranspiration is primarily dominated by water availability rather than energy (or PET). The main advantage of SZI is that, instead of PET, it uses a variable termed climatically appropriate precipitation for existing conditions (P ˆ) as the atmospheric water demand metric. Investigating droughts over 32 large basins across the globe, we show that the SZI can better represent meteorological, hydrological, and agricultural droughts compared to SPEI (especially in non-humid basins; 18 out of 32 basins) and scPDSI at multiple time scales. Given that SZI is physically more reasonable in reflecting surface water-energy balance over both humid and non-humid regions, it enables better characterization of different types of droughts in different climatic regions. [ABSTRACT FROM AUTHOR]

Urban evapotranspiration (ET) is one of the most important components of water and energy balance, and carbon cycle in urbans. It is also a natural process that is powerful enough to possibly mitigate the negative effects caused by urbanization and global warming. Increasing or regulating urban ET could possibly be a solution to overcome the negative impacts caused by urbanization and global warming. Since 2000, researches on urban ET have been increasing and significant progresses have been achieved. A review of these progresses will certainly further promote the related researches and social practices, however, there is yet no such a review article available. Therefore, this article reviewed almost all the published papers on urban ET over the world, summarized its current progresses, scientific understandings, and forecasted the possible challenges in the future. Results achieved from this review would be helpful to use the power of ET to improve the livability of cities, guide the practices of sponge city construction and low impact development, mitigate the negative effect of urban heat island, and reduce urban carbon emission. [ABSTRACT FROM AUTHOR]

[Display omitted] • Impacts of extreme drought event were modelled in large lake-floodplain wetland. • Extreme drought accelerates floodplain groundwater discharge and losing condition. • Groundwater discharge volume in 2022 is about 14.5 times than a normal year. • Reduction in rainfall and lake level exerts substantial impacts on groundwater. The 2022 extreme drought in Poyang Lake (China) caused severe damage to a wide range of sectors. It also emphasized the fact that, even in regions with abundant surface water resources, groundwater resource is still a crucial component of drought management strategies. However, providing up-to-date assessments of groundwater response remains challenging due to the limited data in complex floodplain settings. This study uses a groundwater flow modeling FEFLOW to investigate the influences of the most extreme drought in 2022 on groundwater hydrology in the floodplain wetland of Poyang Lake. Model simulation indicates that the extreme drought led to a significant decrease in floodplain groundwater levels, with a maximum drop of about 5 m. In addition, the extent of the groundwater level drop varies significantly across the floodplain wetland, particularly for the strongest impact (drop > 4 m) occurring in the eastern area of the floodplain. It is expected that the extreme drought accelerates the groundwater discharge rate that is about 3 times than that of the normal year, and thus resulting in a losing condition of the floodplain wetland. On an annual scale, the groundwater discharge of the floodplain wetland in 2022 is estimated to be about 14.5 times than that of a normal year, demonstrating a significant attenuation of groundwater storage under drought environments. The reduction in rainfall combined with the associated low lake level is most likely to exert substantial influences on reduced floodplain groundwater storage. This study is the first attempt to interrogate the response of wetland groundwater to the unpredictable drought event in Poyang Lake, contributing to improved understanding of future water resources allocation and drought resistance strategy. [ABSTRACT FROM AUTHOR]

While early efforts to reduce external phosphorus (P) loads to Lake Erie eliminated the worst eutrophication symptoms in the 1970s and 1980s, the observed intensification of these symptoms in recent decades is difficult to explain by changes in the external P loading alone. We hypothesized that, in addition to external inputs, in-lake processes that release P to the water column may be contributing to the re-eutrophication of Lake Erie. Directly measuring these internal inputs is challenging and their scaling up to the entire lake system remains fraught with uncertainty. To constrain the magnitude of the net P input associated with in-lake processes, we generated a long-term annual total P (TP) budget for the Lake St. Clair–Lake Erie system, averaged over a 14-year period, from 2003 to 2016. The budget shows that the TP output from the system substantially exceeds the sum of the external TP inputs. To balance the budget, we estimate that in-lake processes add a net internal TP load of 3783 metric tons per year (MTA) to the water column. In comparison, the mean yearly external TP load to the Lake St. Clair–Lake Erie system is 11,703 MTA. Thus, overall, in-lake processes account for about a quarter of the total (external plus internal) TP input. The internal input is not evenly distributed among the system's basins, however, with Lake St. Clair and Lake Erie's western, central, and eastern basins receiving 6, 13, 21 and 60% of the total internal P input, respectively. Our results highlight the importance of accounting for the internal P loading in nutrient cycling modeling and load reduction strategies for large lake systems. [Display omitted] • Net phosphorus (P) output from Lake Erie substantially exceeds external inputs. • Internal P inputs represent about a quarter of Lake Erie's total P input. • Internal inputs include sediment efflux, shoreline erosion and sediment resuspension. • Internal P loading may contribute to the re-eutrophication of Lake Erie. [ABSTRACT FROM AUTHOR]

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. • Water and energy budgets were performed for two watersheds. • Measurements included eddy-covariance evapotranspiration, precipitation and discharge. • Local and remote-sensing soil moisture data was used to improve storage estimates. • Water budget closure was worst when soil moisture was most variable. • Good evapotranspiration estimates were obtained from various storage measurements. [ABSTRACT FROM AUTHOR]

This paper examines the coupled effects of weather condition, crop coverage change, and regional water management (i.e., releases from Caballo Reservoir) on hydrologic characteristics of Rincon Valley (2466 km 2 ), a semi-arid agricultural area in New Mexico, U.S.A., using Soil and Water Assessment Tool (SWAT). The model simulates the vertical water budget and horizontal water transfers during the period 1994–2013, incorporating irrigation of fourteen crops in normal (2008) and dry (2011) years to evaluate the hydrologic impacts of cropping change as a drought-adaptive water management strategy. It was calibrated (2000–2002) and validated (2003–2005) using daily-observed streamflow data. Furthermore, evapotranspiration, diversion and irrigation water volume were verified for the period of 2000–2005 using monthly crop irrigation requirement data and canal discharge data. Results demonstrate the significant role of surface water infiltration, providing approximately 18% of the average annual groundwater recharge during the irrigation season. Watershed scale evapotranspiration (ET) and return flows for the irrigation season were estimated to be 23% and 1% higher than those for the non-irrigation season, respectively. For irrigation units, the ratio of ET to combined precipitation and irrigation water for the dry year was 5% higher than the normal year whereas surface runoff, soil water storage, and groundwater recharge were 7%, 17%, and 39% lower than the normal year, respectively. High groundwater recharge occurs in the hydrologic response units (HRU) where corn and cotton are planted on silty clay loam soil. The Alfalfa acreage (i.e., the largest water user) was reduced by 15% while the cotton acreage was increased by 13% in order to adapt to lower water availability during the dry year. Quantitative understanding of the hydrologic fluxes in the Rincon Valley’s irrigated agricultural area illuminates adaptive land and water management to buffer the adverse impacts of prolonged droughts. [ABSTRACT FROM AUTHOR]

The Three-River Source Region (TRSR) of the Tibetan Plateau (TP) is regarded as the “Chinese water tower”. Climate warming and the associated degradation of permafrost might change the water cycle and affect the alpine vegetation growth in the TRSR. However, the quantitative changes in the water budget and their impacts on the vegetation in the TRSR are poorly understood. In this study, the spatial-temporal changes in the hydrological variables and the normalized difference vegetation index (NDVI) during 2003–2014 were investigated using multiple satellite data and a remote sensing energy balance model. The results indicated that precipitation showed an increasing trend at a rate of 14.0 mm 10 a −1 , and evapotranspiration (ET) showed a slight decreasing trend. The GRACE-derived total water storage (TWS) change presented a significant increasing trend at a rate of 35.1 mm a −1 . The change in groundwater (GW) which showed an increasing trend at a rate of 18.5 mm a −1 , was estimated by water budget. The time lag of the GRACE-TWS that was influenced by precipitation was more obviously than was the GLDAS-SM (Soil Moisture) change. The vegetation in the TRSR was greening during the study period, and the accumulation of the NDVI increased rapidly after 2008. The effect of total TWS and GLDAS-SM on vegetation was considerably more than that the effects of other factors in this region. It was concluded that the hydrological cycle had obviously changed and that more soil water was transferred into the GW since the aquiclude changed due to climate warming. The increasing area and number of lakes and the thickening of the active layer in the permafrost area led to the greater infiltration of surface water into the groundwater, which resulted in increased water storage. [ABSTRACT FROM AUTHOR]

The installation of tilting-angle solar panels above agricultural plots provides renewable energy and means of action to dampen some of the effects and hazards of climate change. When the panels are properly operated, their drop shadow reduces water consumption by the plants, as a consequence of alternating shade and sun bands with a short-term impact on the stomatal conductance and a global decrease of gas exchanges. This urged the development of a new model for crop growth and water budget, adapted here from existing literature to handle such transient conditions, characterized by short-term (infra-day) fluctuations. The main difficulty was to combine short-term fluctuations in the climatic forcings (radiation interception and rain redistribution by the panels) and long-term agronomic evaluation, hence the coexistence of several calculation time steps in model structure. All field experiments were conducted on purpose in the agrivoltaic plot of Lavalette (Montpellier, France). Specific adaptations consisted in describing the stomatal behavior of the plants for fluctuating solar radiations and varied water status, aiming at improving both the piloting of the solar panels and water management, i.e. the choice of irrigation amounts. Model simulations have been able to reproduce the expected benefits from agrivoltaic installations, for example showing that it is possible to improve land use efficiency and water productivity at once, by reducing irrigation amounts by 20%, when tolerating a decrease of 10% in yield or, alternatively, a slight extension of the cropping cycle. Agrivoltaism appears a solution for the future when facing climate change and the food and energy challenges, typically in the rural areas and the developing countries and especially if the procedure presented here proves relevant for other crops and contexts. [ABSTRACT FROM AUTHOR]

Information-based policy instruments are some of the most commonly used tools for influencing consumers' water use in the residential sector. However, their ability to change behavior remains an area in need of further research. This study describes the evaluation of an information-based demand management program, rooted in normative comparison, designed to increase the efficiency of households' residential outdoor water use. Results indicate that the program had an impact on water use among households that received persuasive messages regarding their past consumption, compared to estimates of lawn water requirements and the water use of neighbors. Additionally, the results demonstrate that the treatment effect gets stronger over time and varies among message recipients as a function of baseline water use. Unanticipated effects of the administration of the messages show an increase in water use among the lowest consuming households. Top users reduced their water use significantly as a function of the persuasive message. The findings suggest that utilities seeking to augment users' water consumption through persuasion must be cognizant of the way that messages are framed, and who receives them, or potentially face unanticipated side effects, and that message repetition may have some additionality. [ABSTRACT FROM AUTHOR]

Due to progressive erosion of the new Urucurituba Channel, the Amazon River has recently captured almost all discharge from the lower Araguari River (Amapá-AP, Brazil), which previously flowed directly to the Atlantic Ocean. These recent geomorphological changes have caused strong impacts on the landscape and hydrodynamic patterns near the Araguari River mouth, especially the alteration of the riverine drainage system and its water quality. Landsat images were used to assess the estuarine landscape morphodynamic, particularly the expansion of the Urucurituba Channel, 80 km from the Araguari River mouth, chronicling its connection to the Amazon River. The results suggest that the Urucurituba developed by headward migration across the Amazon delta; this is perhaps the first observation of estuarine distributary network development by headward channel erosion. The rate of Urucurituba Channel width increase has been ≈ 5 m/month since 2011, increasing drainage capacity of the channel. We also collected in situ hydrodynamic measurements and analyzed 17 water quality parameters. Having 2011 as baseline, the flowrate of Araguari River has been diverted by up to 98% through Urucurituba Channel, with substantial changes in net discharge recorded at 3 monitoring stations. Statistically significant differences in water quality ( p < 0.05) were observed between 2011 and 2015, associated with the change in the flow pattern. Estuarine salinity and solids concentrations have increased. Overall, we demonstrate changes in landscape, hydrodynamics and water quality of the lower Araguari River. [ABSTRACT FROM AUTHOR]

Oasis areas of arid inland river basins in northwest China have been facing intensified water use conflicts between agricultural sector and eco-environmental systems since 1990s. The reduction of river water allocation to oasis has resulted in the undesirable declines of groundwater levels (GWLs) with the increase in irrigated area and groundwater pumping. Improving water management and restoring GWLs become a great concern for those areas. In this study, the middle oasis of Heihe River basin (HRB) was selected as the representative case for such an endeavor. A three-dimensional groundwater flow model was established for the Zhangye basin, a sub-basin of HRB to obtain a better understanding of groundwater dynamics in middle oasis, particularly for investigating the effects of agricultural water use. A major advantage of this model is that the spatial and temporal recharge from irrigation has been described in details with considering the result obtained by an ago-hydrological model (SWAP-EPIC) simulation. The model was well calibrated and validated over the period of 1991–2010. Simulation of GWLs matched well with the observed 20-year GWLs in the 50 wells. Then, spatiotemporal groundwater dynamics and groundwater budget were quantitatively analyzed for the Zhangye basin during 1991–2010. In particular, the modeling results revealed three different changing trends of GWLs based on the analysis of groundwater dynamics and budget for four representative zones. Results indicated that negative balance of groundwater was mainly caused by over exploitation of groundwater for irrigation, resulting in a GWL decline of 9 cm a −1 in average and even 2 m decline in some years at local areas. The area with critical groundwater depth (e.g. <5 m) has reduced about 30% in 2010 as compared to that in 1991. Finally, recommendations on how to restore GWLs were proposed with emphasis on irrigation water and land use adjustment and groundwater pumping control. Our results are expected to provide implications for recovering the groundwater status in oasis areas of inland river basins in arid northwest China. [ABSTRACT FROM AUTHOR]

Excess nitrogen (N) export from lowland artificial watersheds (polders) is often assumed to be a major contributor to the cultural eutrophication of downstream aquatic ecosystems. However, the complex transport processes characterizing lowland areas pose significant challenges in accurately quantifying their actual role. In this study, we developed a dynamic model to track N sources and transport pathways in lowland polders. The model is able to accommodate all the unique characteristics of polder dynamics, including artificial drainage, and interactions among surface water, groundwater and soil water. Our model was calibrated and validated against water level data and nitrogen concentrations measured in a lowland polder (Polder Jian) in China during the 2014–2016 period. Model performance was satisfactory with an R 2 value of 0.55 and an NS value of 0.53 for total N concentrations. The characterization of the various components of water budget and N cycle derived by the model was on par with local empirical estimates. N export from Polder Jian was approximately 57 kg ha −1 yr −1 and was distinctly higher than values reported from nearby non-polder areas. The largest fraction of N export stemmed from seepage. To our knowledge, this is the first dynamic model to quantify N export from a watershed with artificial drainage network and can be used to design remedial measures of ecosystem degradation. [ABSTRACT FROM AUTHOR]

Fire is a fundamental Earth system process and the primary ecosystem disturbance on the global scale. It affects carbon and water cycles through changing terrestrial ecosystems, and at the same time, is regulated by weather and climate, vegetation characteristics, and, importantly, human ignitions and suppression (i.e., the direct human effect on fire). Here, we utilize the Community Land Model version 4.5 (CLM4.5) to quantify the impacts of changes in human ignition and suppression on fire dynamics and associated carbon and water cycles. We find that the impact is to significantly reduce the 20th century global burned area by a century average of 38 Mha/yr and by 103 Mha/yr at the end of the century. Land carbon gain is weakened by 17% over the 20th century, mainly due to increased human deforestation fires and associated escape fires (i.e., degradation fires) in the tropical humid forests, even though the decrease in burned area in many other regions due to human fire suppression acts to increase land carbon gain. The direct human effect on fire weakens the upward trend in global runoff throughout the century by 6% and enhances the upward trend in global evapotranspiration since ~ 1945 by 7%. In addition, the above impacts in densely populated, highly developed (if population density > 0.1 person/km 2 ), or moderately populated and developed regions are of opposite sign to those in other regions. Our study suggests that particular attention should be paid to human deforestation and degradation fires in the tropical humid forests when reconstructing and projecting fire carbon emissions and net atmosphere-land carbon exchange and estimating resultant impacts of direct human effect on fire. [ABSTRACT FROM AUTHOR]

During the last decades, satellite observations have increasingly been used to study the global water cycle over land. Although their value is now appreciated by the hydrological community, they are still limited by their uncertainties and their inability to close the water budget. In a previous study, we optimally integrated several datasets for each component (precipitation, evapotranspiration, storage change and discharge) to close this budget at a basin scale. Furthermore, an independent and simple calibration of each satellite dataset was designed to reduce the budget residual. In this paper, we extend the calibration procedure to the global scale. Pixels are first classified into surface types characterized by their NDVI and net precipitation values. We show that the global calibration transforms the original datasets towards a consensus that is hydrologically more coherent, with a budget residual reduced by 26%. The calibrated datasets are compared to ground-based observations, showing an improvement for more than 65% of the sites tested. This opens new perspectives to generate long-term datasets at global scale based purely on all available satellites observations, which describe all the terrestrial water components useful for climate purposes. Beyond the simple calibration presented here, inconsistencies among the various satellite datasets can be used as a proxy for satellite observation uncertainties. The quality of our calibration procedure is constrained by the availability of discharge measurements, and could therefore be improved in the future, as discharge measurement networks become more extensive. [ABSTRACT FROM AUTHOR]

• There was significant spatial consistency between the water budget imbalance index and soil aridification. • The more dramatic increase in the actual evapotranspiration (ET) compared to precipitation has kept the trend of soil aridification persisting. • The weaker water storage capacities of croplands than of grasslands resulted in a higher incidence and intensity of soil aridification in croplands than in grasslands. • Cropland-to-grassland conversions enhanced the water storage capacity and mitigated the threat of soil aridification compared to grassland-to-cropland conversions. • Irrigation had a negative impact on the surrounding soil water ecosystems at least 2,000 m away. Understanding the impact of human activities on changes in surface dryness/wetness is crucial for the sustainable development of terrestrial ecosystems. The farming-pastoral ecotone of northern China (FPENC) is experiencing obvious soil aridification under ongoing climate change. The impacts of human activities on cropland and grassland vary. However, how human activities affect soil aridification in terms of cropland and grassland remains unclear. To fill this knowledge gap, this impact mechanism based on the remote sensing retrieval of aridification index and the construction of water budget mismatch index(WMI) is quantified in this study. The results demonstrate a strong spatial consistency between the WMI and the trend of soil aridification. In particular, the trend of soil aridification in the west-central and northeastern areas remained unmitigated where the WMI was less than one. This was due to a more dramatic increase in evapotranspiration (ET) (+64.7 mm) compared to precipitation after subtracting runoff (P i) (+53.9 mm) in the decade between 2001 and 2019. Under the same climatic conditions, croplands had higher crop evapotranspiration and lower soil water storage capacities (WSC) than grasslands, resulting in the aridification intensity of croplands being 1.3 times greater than that of grasslands. Moreover, irrigation exacerbated the depletion of regional groundwater and intensified soil aridification in adjacent drylands and grasslands within a radius of at least 2000 m. These findings provide a scientific foundation for comprehending the mechanism of aridification, developing ecological restoration strategies, and promoting regional sustainable development in the FPENC. [ABSTRACT FROM AUTHOR]

The Everglades Stormwater Treatment Areas (STAs) retain phosphorus (P) from stormwater runoff before it enters the Everglades Protection Area. These large treatment wetlands are extremely efficient in reducing total P (TP) concentrations. However, in some cases, the STAs may require additional measures to reach and/or maintain mandated discharge TP concentrations. One such option, a Periphyton-based Stormwater Treatment Area (PSTA) Cell, was constructed in 2005 on 40 ha at the outflow region of one flow-way in STA-3/4. This PSTA Cell was built to determine operational and engineering requirements associated with the implementation of this technology on a large scale. The PSTA Cell has supported an oligotrophic, periphyton-rich treatment wetland over its operational period of record. This system has consistently produced annual flow-weighted mean (FWM) outflow TP concentrations at or near the mandated outflow TP levels. The PSTA Cell maintained optimal treatment performance when subjected to hydraulic conditions observed in other full-scale STA cells (i.e., deeper water depths, pulsed flows, and major storm events). The PSTA Cell's treatment performance appeared to be better (FWM outflow concentrations ∼9 μg L−1) during continuous flows for 21 days compared to intermittent flow periods. Daily PSTA Cell outflows often were ≤ 13 μg L−1 when inflow TP concentrations were ≤ 22 μg L−1. The PSTA Cell also removed additional P from very low inflow concentrations (< 15 μg L−1). Seepage into the PSTA Cell occurred when its stage was lower than stages in adjacent water bodies, but seepage was greatly reduced when stages in the PSTA Cell were increased and the difference in stage between the PSTA Cell and adjacent bodies was reduced. TP concentrations in seepage water were usually higher than the PSTA Cell's inflow or surface water TP concentrations, therefore, the PSTA Cell performance did not benefit from seepage inflows. Over the 13 water years of operation, accretion of new soil (TP < 300 mg kg−1) did not result in nutrient gradients within the PSTA Cell that might affect P performance. Overall, the PSTA Cell study achieved its goal of providing operational and engineering insights for the implementation of this technology on a larger scale, and the PSTA Cell consistently attained ultra-low-P concentrations (mean ± standard deviation) of 10 ± 3 μg L−1 over its operational period of record. [Display omitted] • PSTA Cell produced daily outflows TP concentrations often ≤13 μg L−1. • Optimal treatment performance was maintained when subjected to hydraulic conditions observed in other full-scale STA cells. • Changes in water depth did not compromise the treatment performance of the PSTA Cell • Long-term sediment accretion did not become a source of P to the water column. • PSTA Cell is an effective and sustainable biological treatment technology able to achieve ultra-low TP concentrations over a long-term period of operation. [ABSTRACT FROM AUTHOR]

River headwaters, in spite of their importance for habitats and water supply, are often inadequately studied and managed. This study discusses the effects of the hydrogeological system and climatic variations on the environment of Monte Fumaiolo (Central Italy), which corresponds to the headwaters of the rivers Tiber, Savio and Marecchia. The area is a key system for supplying drinking-water and is also the habitat of amphibians such as the endemic and endangered Bombina pachypus and other amphibian species. Ongoing climate change is affecting the area: during the last 30 years, five prolonged droughts have occurred, against only one in the preceding 40 years. On all time-scales, there is a decrease in rainfall during the recharge period and an increase of temperature: these trends correspond to a decrease in water yield of about 12% over the last 30 years. The hydrologic system of the study area is composed of one basic aquifer and a few perched aquifers feeding springs. Their resilience to drought depends on their geological setting: study of some depletion curves helped us to understand the geological setting of the various types, and two promising sites for the habitat preservation of amphibians were identified. Study results indicate new approaches to the study and management of the environment and its water supply, which could be useful in similar areas. [ABSTRACT FROM AUTHOR]

Direct groundwater discharge delivers nutrients from land and lakebed sediments to the Great Lakes, which impacts lake water quality. Broad spatial distributions of discharging groundwater are often difficult to measure directly. We present high resolution estimates of direct groundwater discharge across 43% of the Great Lakes coastline based on a water budget approach that uses hydroclimatic models and high-resolution hydrographic data available within the United States. We also integrate land use data to identify coastal areas vulnerable to high groundwater-borne nutrient loads. Estimated rates of direct groundwater discharge along the Great Lakes coast are highly variable, but generally are greatest for Lake Erie and Lake Michigan. Almost one-third of Lake Erie’s United States coastline is vulnerable to groundwater sources of nutrients. To assess uncertainties and limitations in our vulnerability analysis, a vulnerable site along Lake Erie was selected for detailed field measurements of direct groundwater discharge rates and nutrient fluxes. Measured discharge rates were significantly lower than water budget-based estimates (354 ± 25 m 3 y −1 m −1 compared to 588 ± 181 m 3 y −1 m −1 ). Dissolved phosphorous concentrations in the lakebed were elevated compared to onshore groundwater, while nitrate concentrations were lower, indicative of a highly reactive sediment-water interface. Some of the measured phosphorus may be locally sourced from desorption of legacy P or mineralization of organic matter in the lakebed, which our vulnerability framework does not include. Much of the land-derived nitrogen may be transformed along groundwater flow paths prior to discharge. While model-based estimates of direct groundwater discharge and vulnerability to nutrient loading are important for managing Great Lakes water quality, direct field observations remain essential for quantifying fluxes. [ABSTRACT FROM AUTHOR]

Strong and persistent low-level winds blowing over the Adriatic basin are often associated with intense precipitation events over Italy. Typically, in case of moist southeasterly wind (Sirocco), rainfall affects northeastern Italy and the Alpine chain, while with cold northeasterly currents (Bora) precipitations are localized along the eastern slopes of the Apennines and central Italy coastal areas. These events are favoured by intense air-sea interactions and it is reasonable to hypothesize that the Adriatic sea surface temperature (SST) can affect the amount and location of precipitation. High-resolution simulations of different Bora and Sirocco events leading to severe precipitation are performed using a convection-permitting model (MOLOCH). Sensitivity experiments varying the SST initialization field are performed with the aim of evaluating the impact of SST uncertainty on precipitation forecasts, which is a relevant topic for operational weather predictions, especially at local scales. Moreover, diagnostic tools to compute water vapour fluxes across the Italian coast and atmospheric water budget over the Adriatic Sea have been developed and applied in order to characterize the air mass that feeds the precipitating systems. Finally, the investigation of the processes through which the SST influences location and intensity of heavy precipitation allows to gain a better understanding on mechanisms conducive to severe weather in the Mediterranean area and in the Adriatic basin in particular. Results show that the effect of the Adriatic SST (uncertainty) on precipitation is complex and can vary considerably among different events. For both Bora and Sirocco events, SST does not influence markedly the atmospheric water budget or the degree of moistening of air that flows over the Adriatic Sea. SST mainly affects the stability of the atmospheric boundary layer, thus influencing the flow dynamics and the orographic flow regime, and in turn, the precipitation pattern. [ABSTRACT FROM AUTHOR]

Two- and three-dimensional Delft3D Flow and Morphology models were constructed for the lower Song Hau distributary channel of the Mekong River in Vietnam to provide insights into the hydrodynamics and sand transport of the channel system. The models were calibrated and validated with data for observed water level, water discharge, velocity, and suspended-sand concentration during the high- and low-flow seasons of 2014 and 2015. The water and sand budgets of the Dinh An and Tran De channels, the two sub-distributaries of the lower Song Hau channel, were calculated, showing that ~73% of the fluvial water discharge and ~90% of suspended sand were transported through the Dinh An channel, while the rest was transported through the Tran De channel in the high-flow season. In the low-flow season, the total fluvial water discharge was < 20% of that in the high-flow season; and ~96% of it was transported through the Dinh An channel and the rest was transported through the Tran De channel. Sand was transported from channels into the ocean in both the Dinh An and Tran De channels during the high-flow season, but from the ocean into the two channels during the low-flow season. The reversed sand flux from ocean into river channels during low-flow season was not observed in field studies. The different behaviors between models and field observations might be caused by the absence of baroclinic effects in the model set up. The Dinh An channel was found to be dominated by ebb tide, in favor of transporting water and sediment to the ocean, and the Tran De channel was dominated by flood tide. In the high-flow season, the residual currents were directed toward the ocean for both the Dinh An and Tran De channels. In the low-flow season, the magnitude of the residual currents decreased in the river channels. Under these conditions, the residual-current direction changed to be ambiguous in the Tran De channel, but remained seaward in the Dinh An channel. The low fluvial discharge combined with strong tides under very low-flow conditions can probably generate a net clockwise water circulation between the Dinh An and Tran De channels, which transports water from the ocean to the river through the Tran De channel, then back into the ocean through the Dinh An channel. The clockwise circulation pattern is likely to influence the channel evolution and impact saltwater intrusion issue in the lower Song Hau channel. [ABSTRACT FROM AUTHOR]

Groundwater potential mapping and its sustainable development are an important aspect in Leh valley due to an increase of tourists and the local population. In the present study, the groundwater potential zones were delineated by adopting a frequency ratio (FR) model. Land use and land cover, hydro geomorphology, slope, geology, lineament density, drainage density, spring well locations and ground water level were the thematic factors considered for groundwater potential zone mapping. There are 86 spring wells located in the study area, of which 60 wells were considered for success rate and remaining 26 wells considered for prediction rate in the FR model. The final groundwater potential map was classified into five zones as very high, high, moderate, low, and very low. The success and prediction rates of FR model were measured as 81.25% and 77.23% respectively. Water budget of the valley was also calculated on the basis of consumption, demand and supply of water by taking account of the floating population. There is a huge demand of water supply requirement during the tourist season from May to September months and deficiency of water in the area was calculated as 4,224,557 (in l). Finally, suitable sites for artificial recharge for sustainable groundwater management were identified. The sites were selected on the basis of depth of groundwater level, source of spring well locations and gradient from natural spring to selected recharge wells. [ABSTRACT FROM AUTHOR]

The estimation of water resources at basin scale requires modelling of all components of the hydrological system. Because of the great uncertainties associated with the estimation of each water cycle component and the large error in budget closure that results, water budget is rarely carried out explicitly. This paper fills the gap in providing a methodology for obtaining it routinely at daily and subdaily time scales. In this study, we use various strategies to improve water budget closure in a small basin of Italian Prealps. The specific objectives are: assessing the predictive performances of different Kriging methods to determine the most accurate precipitation estimates; using MODIS imagery data to assist in the separation of snowfall and rainfall; combining the Priestley-Taylor evapotranspiration model with the Budyko hypothesis to estimate at high resolution (in time and space) actual evapotranspiration (ET); using an appropriate calibration-validation strategy to forecast discharge spatially. For this, 18 years of spatial time series of precipitation, snow water equivalent, rainfall-runoff and ET at hourly time steps are simulated for the Posina River basin (Northeast Italy) using the JGrass-NewAGE system. Among the interpolation methods considered, local detrended kriging is seen to give the best performances in forecasting precipitation distribution. However, detrended Kriging gives better results in simulating discharges. The parameters optimized at the basin outlet over a five-year period show acceptable performances during the validation period at the outlet and at interior points of the basin. The use of the Budyko hypothesis to guide the ET estimation shows encouraging results, with less uncertainty than the values reported in literature. Aggregating at a long temporal scale, the mean annual water budget for the Posina River basin is about 1269 ± 372 mm (76.4%) runoff, 503.5 ± 35.5 mm (30%) evapotranspiration, and − 50 ± 129 mm ( − 4.2%) basin storage from basin precipitation of 1730 ± 344 mm. The highest interannual variability is shown for precipitation, followed by discharge. Evapotranspiration shows less interannual variability and is less dependent on precipitation. [ABSTRACT FROM AUTHOR]

Mediterranean ecosystems are particularly vulnerable to the environmental changes which have occurred in the last decades. Evaluating the ecosystem response to these changes is therefore a top priority, particularly concerning water and carbon dynamics. The Pianosa Island is a well known test site where numerous environmental surveys have been performed to fully characterize the most typical vegetation type, Mediterranean macchia. A first measurement campaign concerning both vegetation and soil properties was performed in 2001, and was repeated in 2010 only for soil properties. Vegetation cover was characterized again by means of an aircraft high resolution LiDAR dataset taken in 2009. Additional medium and low spatial resolution satellite images (Landsat OLI and MODIS) and aircraft photos were recovered from various sources. The availability of these datasets offers a unique opportunity to develop and test a methodology capable of modelling and analyzing the water and carbon dynamics of Mediterranean macchia during the 2001–2010 decade. To this aim, simulation procedures integrating remotely sensed and ancillary data were first tuned towards the available observations of vegetation biomass and soil carbon content. These procedures were then applied to produce daily estimates of macchia actual evapotranspiration (AET), gross primary production (GPP) and net ecosystem exchange (NEE), whose accuracy was assessed against corresponding eddy covariance flux tower observations taken in two years (2007–2008). The results obtained are satisfactory and support the capability of the modelling approach to reproduce both the water and carbon dynamics of macchia during the study decade. From an ecological viewpoint, both fluxes are increasing in this time period, mainly depending on similarly increasing spring rainfall. The macchia ecosystem behaves as a net sink of carbon, which is stored primarily in soil (≅90%) and secondarily in vegetation. [ABSTRACT FROM AUTHOR]

This study evaluates the alternative conceptual models for groundwater modelling. A true model was created with a synthetic alluvial fan-plain hydrogeological framework. Various alternative conceptual models were evaluated for groundwater flow simulations. The first alternative model is a single aquifer layer model; the second alternative model is a 3-layer aquifer model; and the third model is a 5-layer model consisting of 3 aquifers separated by 2 aquitards. All models could fit very well to the observations with optimized values of hydraulic conductivities. However, the single aquifer layer model can only compute water balance components with good accuracy. The 3-layer aquifer model can be used for water balance computation and groundwater head simulation with small errors. The 5-layer model is capable of simulating water budget, groundwater head distribution and travel times with high accuracy. Multi-model analysis found only the 3rd alternative model superior. [ABSTRACT FROM AUTHOR]

The traditional soil management practice used in rainfed orchards in the Chinese Loess Plateau is clear cultivation (bare soil). This system leads to severe water erosion and considerable loss of water as runoff during heavy rainfall, especially on steep slopes. Plant cover systems represent a controversial alternative to the clear cultivation system. Although cover plants strongly promote water infiltration during rainfall, they may also compete with the trees for limited soil water. In this study, water regimes and inhibition of jujube ( Ziziphus jujube Mill. ) tree photosynthesis by water stress were compared across two types of soil management strategy: 1) a traditional clear cultivation system (CC); and 2) three plant cover systems (PCS) using different species, namely birdsfoot trefoil ( Lotus corniculatus L.), cocksfoot ( Dactylis glomerata L.) and white clover ( Trifolium repens L.), in constructed soil macrocosms (0.8 × 0.8 × 2.0 m) under simulated rainfall regimes. The PCS resulted in the infiltration of significantly more water during a rainfall event of about 60 mm (infiltration coefficients 86%–91% for PCS and 68% for CC). The superior infiltration achieved in the PCS treatments was then gradually offset by their extra water consumption compared with that of CC. During a light rainfall event (rainfall amount: 30 mm), runoff became negligible (less than 1.5% of the total rainfall amount) and the plant cover systems had mainly negative effects, including faster development of drought and water-mediated photosynthesis inhibition in jujube leaves. The white clover cover treatment showed the lowest runoff (runoff coefficient: 15% for the heavy rainfall and 3% for the light rainfall), the most conservative water consumption and the weakest inhibitory effects on jujube photosynthesis (net assimilation rate: >8 μmol CO 2 m −2 s −1 ) among the three plant cover treatments. The white clover cover treatment is thus recommended as the most suitable choice for jujube orchards in the Loess Plateau area. [ABSTRACT FROM AUTHOR]

Understanding the hydrologic processes of inland lake basins in the Tibetan Plateau (TP) could provide insights into the responses of Tibetan lake dynamics to climate change. An efficient approach for this purpose is to represent complex hydrologic behaviors of such Tibetan lake watersheds with plausible hydrologic models. In this study, water level fluctuations of Lake Nam Co, an inland lake in the central TP, were investigated using a lumped lake-watershed model. The degree-day factor method was introduced to improve the model applicability in glacier-covered basins. The model simulated the hydrologic processes as well as the lake water budget. Remote sensing images (Landsat MSS, TM, ETM + and OLI) from 1972 to 2015 were used to identify the glacier and lake boundaries. Multisource climate data (e.g., ground point observation, 0.25 o gridded APHRODITE and TRMM 3B42 v7 precipitation products) were used to drive the hydrologic model at a monthly time step. Results of trend analysis showed that basin-wide annual air temperature increased by the rate 0.04 °C/yr from 1961 to 2015. Mean annual precipitation slowly increased from 1961 to the mid-1990s, and then rapidly increased from the late-1990s to the mid-2000s, and finally obviously decreased after the mid-2000s. As a response to climate change, glaciers decreased by 62.69 km 2 (29%) and lake area increased by 91.83 km 2 (4.7%) from 1972 to 2015. The analysis of lake water budget suggested that, the total basin runoff and on-lake precipitation contributed 1.36 km 3 /yr (66%) and 0.7 km 3 /yr (34%), respectively, to mean annual water gain of the lake. Glacier runoff was 14% of the basin runoff and 10% of the total water gain of the lake. The percentages of lake evaporation, water seepage and water surplus were 65%, 20% and 15%, respectively. Lake level increased with the rate of 0.14 m/yr for the study period 1961–2015. It could be concluded that precipitation was the dominant controlling factor for the different magnitudes of lake level rising rates of 0.10, 0.41 and 0.06 m/yr for the periods of 1961–1998, 1999–2008 and 2009–2015, respectively. [ABSTRACT FROM AUTHOR]

Effective Monthly Recharge (W em ) calculations use historical weather data to estimate monthly-scale water level changes in precipitation-and-groundwater-driven wetlands. This time-weighted water-budget procedure relates first-of-the-month hydraulic heads measured in a monitoring well or small pond with precipitation and evapotranspiration data for preceding months and generates a regression equation used to estimate historic water levels. This study developed an enhanced procedure more robust than used with previous W em studies. Two data sets of water-table fluctuations in humid-temperate southeastern Virginia (U.S.A.) allowed verification of the model procedure—a 30-year record from a shallow well maintained by the U.S.G.S., and a 6.5-year record from a mitigation wetland measured before and after construction. Analyses of Predicted Heads and Observed Heads at both sites indicate that the W em model can replicate reasonably the seasonal patterns of water-table fluctuations and the range of values of hydraulic heads at a monthly scale. Within the limitations set by the assumptions of the procedure and the range of water fluctuations during the calibration period, W em calculations may be used to generate synthetic hydrographs for periods with appropriate weather data. Analyses of two sites in Missouri and Nebraska (U.S.A.) suggest that the W em procedure may prove useful also in climatic regions with relatively strong seasonal forcing, but additional testing is needed to verify the range of model applicability. These reconstructions could support long-term decisions in the management of wildlife habitats or design of mitigation wetlands. [ABSTRACT FROM AUTHOR]

A 3D coupled physical-biogeochemical model is developed and applied to Bizerte Lagoon (Tunisia), in order to understand and quantitatively assess its hydrobiological functioning and nutrients budget. The biogeochemical module accounts for nitrogen and phosphorus and includes the water column and upper sediment layer. The simulations showed that water circulation and the seasonal patterns of nutrients, phytoplankton and dissolved oxygen were satisfactorily reproduced. Model results indicate that water circulation in the lagoon is driven mainly by tide and wind. Plankton primary production is co-limited by phosphorus and nitrogen, and is highest in the inner part of the lagoon, due to the combined effects of high water residence time and high nutrient inputs from the boundary. However, a sensitivity analysis highlights the importance of exchanges with the Mediterranean Sea in maintaining a high level of productivity. Intensive use of fertilizers in the catchment area has a significant effect on phytoplankton biomass increase. [ABSTRACT FROM AUTHOR]

• We analyzed future climate impacts on hydrological extremes in Upper Blue Nile Basin. • We used the wettest and driest CMIP5 projections as inputs to the CREST-SVAS model. • We studied the effectiveness of the dam operation to moderate extreme event severity. • GERD can reduce flood and drought intensity by adjusting seasonal water release. • Expected hydropower generation (15,000 GWh/year) can be met in a wet climate scenario. Climate change poses a great threat to society through its effects on extreme hydrological events (floods and droughts) and the sustainable development. Coping with climate change requires a better awareness of the possible impacts to inform climate adaptation strategies. In this study, we investigated the climate projections from two contrasting GCMs (wet scenario from MIROC5 and dry scenario from CSIRO) and quantified the possible outcomes in terms of hydrological components of the Upper Blue Nile Basin (UBNB). These two climate projection scenarios show that the overall precipitation change in the early (2011–2040), mid (2041–2070), and late century (2071–2100) over the UBNB may vary from –18.3 % to + 13.6 % of the baseline annual precipitation of 1350 mm. The hydrological simulations over the basin from our study showed that evapotranspiration may vary between –13.7 % and + 12.1 % of the average annual total actual ET of 710 mm, and the flow at the basin outlet may range between –40.7 % and + 30.8 % of the mean annual total flow volume of 45 billion cubic meters. As a result, the wet projection exhibited more frequent floods while the dry projection showed severe droughts, specifically in the late century. We also examined the role of the Grand Ethiopian Renaissance Dam (GERD), designed for hydropower generation, in moderating these potential future climate hydrological extremes. Our findings indicate that GERD operations can help reduce downstream flood and drought severity by managing flow releases. Thus, this study illustrates the most possible extreme hydrological events in the UBNB due to climate change and demonstrates the degree to which GERD operations can help reduce the impact of these extremes downstream. The findings and data generated in this study will aid understanding the importance of sustainable water management and reservoir operation that caters to both hydropower generation, and recurring floods and droughts. [ABSTRACT FROM AUTHOR]

This paper presents a study of the potential for green infrastructure (GI) to restore the predevelopment hydrologic cycle in a semi-arid urban catchment. Simulations of stormwater runoff from a 0.11-km 2 urban catchment in Salt Lake City, Utah, USA for predeveloped (Natural Hydrology, NH), developed (Baseline, BL), and developed with GI (Green Infrastructure, GI) conditions were executed for a one-year period. The study was repeated for a relatively dry year, wet year, and an average year based on precipitation amounts in the year. Bioretention and green roofs were chosen for the GI plan. Results showed that the water budget of the catchment with the GI plan implemented more closely matches the NH water budget compared to the BL scenario, for all three years (dry, wet, average). The BL and GI scenarios showed more significant modifications to the water budget than what has been found by studies in humid climates. Compared to the BL condition, GI annually reduces surface runoff by 35%, 45%, and 43% and restores evapotranspiration by 18%, 19%, and 25% for the dry, average, wet years, respectively. Based on the introduced water budget restoration coefficient (WBRC), the water budget of the study catchment was restored by the GI plan to 90%, 90%, and 82% of the predevelopment state in the dry, average, and wet years, respectively. By comparing the WBRC estimated for other studies, it is further inferred that the water budget is more significantly affected by development and GI restoration in semi-arid than humid climates, but the differences lessen as the precipitation amount increases. [ABSTRACT FROM AUTHOR]

The sustainability of urban water systems is often compared in small numbers of cases selected as much for their familiarity as for their similarities and differences. Few studies examine large urban datasets to conduct comparisons that identify unexpected similarities and differences among urban water systems and problems. This research analyzed a dataset of 142 cities that includes annual per capita water use (m 3 /yr/cap) and population. It added a 0.5 ° grid annual water budget value (P-PET/yr) as an index of hydroclimatic water supply. With these indices of urban water supply and demand, we conducted a hierarchical cluster analysis to identify relative similarities among, and distances between, the 142 cases. While some expected groupings of climatically similar cities were identified, unexpected clusters were also identified, e.g., cities that use water at greater rates than local climatic water budgets provide. Those cities must seek water from greater distances and greater depths. They face greater water and wastewater treatment costs. To become more sustainable they must increase water use efficiency, demand management, reuse, and recycling. The significance of the population variable suggests that adding other explanatory socio-economic variables, as well as more precise water system indices, are logical next steps for comparative analysis of urban water sustainability. [ABSTRACT FROM AUTHOR]