Average Annual Recharge Research Articles

Estimation of Spatially Distributed Groundwater Recharge in Data-scarce Regions

Study RegionUpper Beles Basin, Ethiopia FocusData limitations significantly challenge accurate groundwater recharge estimation, especially in regions with sparse gauging stations and highly variable hydro-meteorological conditions, such as the Upper Beles Basin, Ethiopia. Using interpolated data often yields unreliable results. This study evaluates the use of remote sensing-based hydro-meteorological data to estimate spatially distributed groundwater recharge in such data-scarce regions, comparing it with point estimates derived from primary field data, using a case study of Upper Beles Basin. New Hydrological Insights for the RegionThe study employed TerraClimate and CHIRPS datasets to estimate spatially distributed recharge using the WetSpass model. Groundwater recharge was also estimated using the Water Table Fluctuation (WTF) and Chloride Mass Balance (CMB) methods, with data from 21 monitoring wells and 45 water samples. The estimated average annual recharge was 420mm (WTF), 308mm (CMB), and 365mm (WetSpass). The substantial variability in point estimates reflects the basin's recharge heterogeneity, indicating the risks of relying solely on point data. A strong correlation (72%) was found between the WTF-derived point estimates and WetSpass-generated values. Recharge variability is influenced by land use in the lowlands and by slope, soil, and rainfall in the highlands. This research demonstrates that remote sensing-based data can yield more reliable recharge estimates in regions with sparse gauging stations and highly variable hydro-meteorological conditions.

Estimation of Groundwater Recharge in a Volcanic Aquifer System Using Soil Moisture Balance and Baseflow Separation Methods: The Case of Gilgel Gibe Catchment, Ethiopia

Understanding the recharge–discharge system of a catchment is key to the efficient use and effective management of groundwater resources. The present study focused on the estimation of groundwater recharge using Soil Moisture Balance (SMB) and Baseflow Separation (BFS) methods in the Gilgel Gibe catchment where water demand for irrigation, domestic, and industrial purposes is dramatically increasing. The demand for groundwater and the existing ambitious plans to respond to this demand will put a strain on the groundwater resource in the catchment unless prompt intervention is undertaken to ensure its sustainability. Ground-based hydrometeorological 36-years data (1985 to 2020) from 17 stations and satellite products from CHIRPS and NASA/POWER were used for the SMB method. Six BFS methods were applied through the Web-based Hydrograph Analysis Tool (WHAT), SepHydro, BFLOW, and Automated Computer Programming (PART) to sub-catchments and the main catchment to estimate the groundwater recharge. The streamflow data (discharge) obtained from the Ministry of Water and Energy were the main input data for the BFS methods. The average annual recharge of groundwater was estimated to be 313 mm using SMB for the years 1985 to 2020 and 314 mm using BFS for the years 1986 to 2003. The results from the SMB method revealed geographical heterogeneity in annual groundwater recharge, varying from 209 to 442 mm. Significant spatial variation is also observed in the estimated annual groundwater recharge using the BFS methods, which varies from 181 to 411 mm for sub-catchments. Hydrogeological conditions of the catchment were observed, and the yielding capacity of existing wells was assessed to evaluate the validity of the results. The recharge values estimated using SMB and BFS methods are comparable and hydrologically reasonable. The findings remarkably provide insightful information for decision-makers to develop effective groundwater management strategies and to prioritize the sub-catchments for immediate intervention to ensure the sustainability of groundwater.

Spatiotemporal recharge estimation in the upper Awash sub-basin, central Ethiopia

ABSTRACT Sustainable groundwater management decisions require an understanding of the spatial distribution and seasonal fluctuations of site-specific water budget computations. This study aims to estimate the spatiotemporal distribution of recharge in the upper Awash sub-basin where the groundwater is experiencing intensive abstraction for domestic, industrial, and irrigation water uses. We estimated the spatial and long-term average monthly, seasonal, and annual groundwater recharge using a GIS-based spatially distributed water balance WetSpass-M model. Distributed grid maps of physical parameters (land-use land cover, soil, and slope) and monthly climatological records (rainfall, maximum and minimum temperature, wind speed) were used as model inputs. The WetSpass-M model estimated recharge is validated with the independently computed recharge using the automated digital filtering baseflow separation method. Attributed mainly to variability in soil texture and land use, the annual precipitation (1,032 mm) is distributed as evapotranspiration (45%), surface runoff (42%), and groundwater recharge (11%). Forest and grass areas with loamy sand have high recharge, while built-up areas with clay soil have low recharge. August to September is estimated to have the largest recharge, while November to December has the lowest. Understanding the spatial and seasonal variability of groundwater recharge is important for sustainable utilization, proper management, and planning of groundwater resources.

Estimating groundwater recharge rates in the Upper Awash Basin, Ethiopia under different combinations of model complexity and objective functions

Abstract This study addresses the critical need for reliable groundwater recharge quantification by investigating the uncertainty associated with recharge estimation based on various combinations of model complexity and objective functions. Focusing on the Hombele catchment in the upper Awash Basin, Ethiopia, the research aims to analyze parameter sensitivity under different model complexities and objectives while estimating groundwater recharge for the period 1986–2013. Employing a Monte-Carlo-based calibration scheme, the study fine-tunes model parameters using objective functions like KGE, NSE, LogNSE, R2, and VE across 10 combinations of model complexity and objective functions. Results identify FC, LP, and BETA as highly sensitive parameters, while UZL, K0, and MAXBAS show limited influence in all model complexity and objective function scenarios. The semi-distributed HBV-light model achieves calibration, validation, and overall period KGE (NSE) values of 0.89 (0.80), 0.80 (0.73), and 0.87 (0.77), respectively. Sensitivity analyses reveal significant impacts on model parameters and recharge estimation based on the chosen objective function and model complexity levels. Average annual recharge rates range from 185.9–280.5 mm when the HBV-light model is semi-distributed, contrasting with 185.3–321.7 mm under lumped model conditions, emphasizing the importance of considering these factors in groundwater resource assessments.

Assessing Groundwater Recharge in the Wabe River Catchment, Central Ethiopia, through a GIS-Based Distributed Water Balance Model

The utilization of groundwater has emerged as an indispensable asset in facilitating economic advancement, preserving ecological integrity, and responding to the challenges posed by climate change, especially in regions characterized by aridity and semi-aridity. The sustainable management of water resources requires an assessment of the geographical and temporal patterns of groundwater recharge. The present study employed the GIS-based WetSpass-M model to model the water balance components by utilizing hydro-meteorological and biophysical data from the Wabe catchment, which spans an area of 1840 km2 in central Ethiopia, for a long time. The objective of this study was to assess the long-term average annual and seasonal groundwater recharge for the catchment area utilizing the WetSpass-M model. The input data were collected through remote sensing data and surveys in the field. The model was employed to gain insights into the process of groundwater recharge in a particular region and to facilitate effective management, prudent utilization, and sustainable planning of water resources in the long run. Water balance components were estimated using seasonal fluctuations in evapotranspiration, surface runoff, and groundwater recharge. The Wabe catchment’s summer, winter, and mean long-term yearly groundwater recharge were determined to be 125.5 mm, 78.98 mm, and 204.51 mm, respectively. The model indicates that summer seasons account for 86.5% of the mean annual precipitation, while winter seasons account for 13.5%. On the other hand, the groundwater system percolates 14.8% of the total annual rainfall (1374.26 mm). While evapotranspiration accounts for 51% of total precipitation and surface runoff accounts for 34.1%, the Wabe catchment’s mean annual evapotranspiration and surface runoff values are simulated at 701.11 mm and 485.58 mm, respectively. The findings suggest the use of the WetSpass-M model to precisely calculate the water balance components within the Wabe catchment.

Evaluation of Aquifer Properties to Categorize Groundwater Potential in a Part of Southwest Bangladesh Using Catastrophe Theory

This paper evaluated aquifer properties in a part of Southwest Bangladesh to categorize groundwater potential using catastrophe theory (CT). Satellite image, lithologic, pumping test, rainfall and groundwater monitoring data were utilized for this purpose. Lithology-based stratigraphic cross- sections confirm six vertically distributed layers, classified into aquitard composed of surface clay with silt and very fine-grained sand with thickness varying from 1 to –24.4 m, whereas the aquifer comprising fine to coarse sand with 3–67 m thick. Pre- and post-monsoon average annual groundwater levels fluctuate from in 3.12 to 3.86 m and 6.97 to 8.36 m, respectively, while average annual recharge ranges from 0.4 to 0.59 m/yr. Groundwater potential index (GWPI) values, validated with specific capacity records, classified the study area into three zones with GWPI of 0.72–0.81 (moderately good), 0.81–0.87 (good), and 0.87–0.96 (very good), covering 25.44%, 47.60%, and 26.96% of the area, respectively. Sensitivity analysis identified rainfall as the most influential and land type as the least influential factor in defining groundwater potentiality. These results can serve as a foundation for the formulation of guidelines and recommendations for the governmental and affiliated agencies for future groundwater exploration, planning, and management.

Recharge Estimation Approach in a Data-Scarce Semi-Arid Region, Northern Ethiopian Rift Valley

Sustainable management of groundwater resources highly relies on the accurate estimation of recharge. However, accurate recharge estimation is a challenge, especially in data-scarce regions, as the existing models are data-intensive and require extensive parameterization. This study developed a process-based hydrologic model combining local and remotely sensed data for characterizing recharge in data-limited regions using a Basin Characterization Model (BCM). This study was conducted in Raya and Kobo Valleys, a semi-arid region in Northern Ethiopia, considering both the structural basin and the surrounding mountainous recharge areas. Climatic Research Unit monthly datasets for 1991 to 2020 and WaPOR actual evapotranspiration data were used. The model results show that the average annual recharge and surface runoff from 1991 to 2020 were 73 mm and 167 mm, respectively, with a substantial portion contributed along the front of the mountainous parts of the study area. The mountainous recharge occurred along and above the valleys as mountain-block and mountain-front recharge. The long-term estimates of the monthly recharge time series indicated that the water balance components follow the temporal pattern of rainfall amount. However, the relation of recharge to precipitation was nonlinearly related, showing the episodic nature of recharge in semi-arid regions. This study informed the spatial and temporal distribution of recharge and runoff hydrologic variables at fine spatial scales for each grid cell, allowing results to be summarized for various planning units, including farmlands. One third of the precipitation in the drainage basin becomes recharge and runoff, while the remaining is lost through evapotranspiration. The current study’s findings are vital for developing plans for sustainable management of water resources in semi-arid regions. Also, monthly groundwater withdrawals for agriculture should be regulated in relation to spatial and temporal recharge patterns. We conclude that combining scarce local data with global datasets and tools is a useful approach for estimating recharge to manage groundwater resources in data-scarce regions.

Interaction between Groundwater and Surface Water in the Qujiang River Basin in China: Evidence from Chemical Isotope Measurements

The Qujiang River Basin is a significant water system located in Zhejiang Province, China, that serves as a primary water source for Quzhou City. For this research, we collected and examined water samples from the Qujiang River Basin. In this study, we collected and analyzed water samples from the Qujiang River Basin and employed a combination of methods, including water balance analysis; Piper trilinear diagram; Gibbs diagram; and environmental tracer techniques, such as hydrochemical and isotopic analysis. These techniques helped us to analyze the spatial distribution patterns and evolutionary trends of surface water and groundwater hydrochemistry, along with the stable isotopes of hydrogen and oxygen, as well as to determine the sources of surface water and groundwater by calculating the conversion ratio between surface water and groundwater. (1) The findings of our study indicate that the primary hydrochemical types in the study area are Ca-HCO3 and Ca-HCO3·Cl, with the ion composition of water primarily influenced by rock weathering and precipitation. (2) Similar spatial variations in hydrochemical indicators were observed between surface water and groundwater in the study area, with frequent transitions between the two. (3) The hydrogen and oxygen isotope content increases downstream, signifying that both groundwater and surface water in the study area are replenished by atmospheric precipitation, as supported by the relationship between hydrogen and oxygen isotopes and the meteoric water line. (4) We determined that groundwater predominantly replenishes surface water in the upstream area. The average contribution rate of groundwater to surface water is 19.67%, with an annual average recharge volume of 1.23 × 106 m3. Midstream and downstream, surface water mainly recharges groundwater, with an average contribution rate of 22.77% and an annual average recharge volume of 1.59 × 106 m3.

Hydrological Modeling and Evaluation of Water Balance Over the Complex Topography of Nile Basin Headwaters: The Case of Ghba River, Northern Ethiopia

Water resource evaluation, management, and conservation at the local, national, and international levels depend on an accurate understanding of the hydrological processes. In data-poor environments and topographically complicated areas like the Ghba subbasin in the headwaters of the Nile River, the function of hydrological models is crucial. The primary goal of this study is to use the WEAP model to simulate the hydrology of the Ghba basin. This is because recent hydrological behaviour has changed significantly and resulted in a serious water deficit. The minimal satisfactory performance limit for the monthly stream flow variable was strongly attained by the multi-variable calibration scenario (R2 = 0.82, NSE = 0.82, IA= 0.80 RSR = 0.87 and PBIAS = 9 % for calibration scenario; and R2 = 0.78, NSE = 0.81, IA= 0.70 RSR = 0.80 and PBIAS = 11.5 % for validation scenario). Evapotranspiration makes up 63.4% of the water balance, according to the model simulation, while surface runoff, interflow, baseflow and groundwater recharge accounting for 11.1 %, 11.8%, 5.4% and 8.3 %, respectively. The simulated average annual streamflow at the subbasin outlet is 16.33 m3/s. The simulated monthly minimum flow occurs in January with an average flow of 1.78 m3/s and a coefficient of dispersion of 0.45. Maximum flows occur in July and August, with an average flow of 53.57 m3/s and a coefficient of dispersion of 0.19. The main rainy season was shown to have a larger spatial distribution of simulated runoff, and the average annual recharge value is 53.5 mm. The study's conclusions indicated that both surface water harvesting and groundwater extraction might be used for reliable water distribution to the subbasin's continuously increasing sectoral water demand.

Energy consumption as a proxy to estimate groundwater abstraction in irrigation

Groundwater irrigated agriculture accounts for approximately 70% of global groundwater withdrawals and around 38% of the total irrigated area. The indiscriminate use of groundwater has resulted in the depletion of groundwater resources across many regions globally. To ensure sustainable use, it is imperative to limit abstraction to within the average annual recharge rate. However, in agricultural systems in many developing countries, including India, where millions of smallholder farmers use individual wells for pumping, monitoring, and reliable data are lacking. This study proposes an energy-based approach to estimate groundwater abstraction, providing a low-cost method for deriving estimates of moderate accuracy. The research focuses on two areas with contrasting aquifer conditions in Gujarat, India: one alluvial and one hard rock. Using pump and well data, a conversion factor (CF) relating to the volume of water abstracted per unit of energy consumed is determined. In hard rock aquifers, the conversion factor decreases from an average of 6.0 m³ kWh−1 for 3 HP pumps to 4.7 m³ kWh−1 for 7.5 HP pumps. In alluvial aquifers characterized by higher aquifer transmissivity and flow rates, the conversion factor decreases from an average of 9.4 m³ kWh−1 for 10 HP pumps to 4.7 m³ kWh− 1 for 20 HP pumps. The developed relationship shows that CF is related to factors such as pump horsepower, well characteristics, groundwater levels, and pump age. The CF relationship with pump and well characteristics is more robust (R2 ∼ 0.75) in alluvial aquifers compared to the hard rock aquifer (R2 ∼ 0.49). The developed models provide satisfactory estimates of groundwater abstraction, with R2 ∼ 0.92 for alluvial aquifers and ∼0.69 for hard rock aquifers, as compared to observed data on groundwater abstraction. This energy-based approach offers a cost-effective means of monitoring groundwater abstraction, particularly crucial in regions with heavily developed groundwater resources.

Analysis of groundwater recharge in Nadvirna district by the Korkmaz method

The identification of groundwater sources and the prediction of possible water level fluctuations are crucial, as the study of these indicators is important for understanding the renewal of water resources and their efficient use in specific territorial conditions. The purpose of this study was to identify groundwater sources in the area of Mykulychyn village and assess their changes during the period from 2016 to 2022. The study was based on the Korkmaz method and analysis of data on water level in the well and precipitation level in the study area. The structural analysis of groundwater recharge in the Mykulychyn village in Nadvirna district was carried out using the Korkmaz method. It is established that groundwater recharge in Mykulychyn village is due to precipitation. The correlation between the water flow rate from the source and the water level in the well is demonstrated, allowing for projection of the study results to both objects. The average annual rainfall on the territory was 1,055.7 mm. The results of the linear regression analysis showed a connection between the water level and the total precipitation. The analysis of water level fluctuations in the well revealed that the annual water level recharge varies from 782 mm in 2017 to -254 mm in 2022. This indicates that some smaller aquifers may have dried up in 2022. The average annual recharge for the period from 2017 to 2022 is 347 mm, which is about 32.88% of the average annual precipitation. The results of the study can be useful in practice for water management and planning in Mykulychyn village, as well as in similar geographical conditions

Implications for sustainable water consumption in Africa by simulating five decades (1965–2014) of groundwater recharge

Groundwater stands as a vital water resource for both present and future generations in Africa. This underscores the importance of examining the sustainability of current groundwater consumption across the continent, along with its capacity to fulfill the current human and essential environmental water needs. Groundwater sustainable yield is a suitable indicator for assessing groundwater sustainability but has not yet been quantified properly across Africa. A thorough quantification of groundwater sustainable yield necessitates a profound comprehension of the spatio-temporal fluctuations in surface hydrology, groundwater recharge, environmental flow, and sectoral water use. In this study, high spatial resolution (10 km) land surface hydrology was simulated for five decades (1965–2014) across Africa by the Community Land Model version 5 at half-hourly time step and aggregated to monthly and annual temporal resolutions. Then, groundwater recharge and environmental flow were quantified based on the water balance approach for the whole continent. Finally, by including African sectoral water use data available for four decades (1971–2010) we obtained the long-term average of groundwater sustainable yield. Based on extensive simulations of long-term land surface hydrology, we discovered that the groundwater system in Africa experienced an average annual recharge of 57.8 mm yr−1 (with a standard deviation of 110.8 mm yr−1 serving as an indicator of spatial variability), corresponding roughly to an annual recharge volume of 1793.6 km3 yr−1. Furthermore, our analysis revealed that the entire continent possesses an annual average potential sustainable yield (with standard deviations) of 4.5 mm yr−1 (10.2), 20.6 mm yr−1 (42.9), and 37.3 mm yr−1 (75.7) under conservative, optimum, and suitable water consumption scenarios, respectively. This calculated annual groundwater sustainable yield corresponds to 141.9 km3 yr−1, 643.1 km3 yr−1, and 1160.5 km3 yr−1 for the conservative, optimum, and suitable scenarios, respectively. Furthermore, the calculated sustainable yield volume is contrasted with the total water storage figures documented for 50 countries throughout Africa. The outcomes illustrate that our calculated annual sustainable yield equates to roughly 0.02%, 0.1%, and 0.17% of the reported groundwater storage across the entire continent. Based on the estimated long-term average sustainable yield and the reported total water storage at the national level, our conclusion is that the accessible groundwater resources could potentially satisfy the current water requirements of both humans and the environment in African countries. This study offers the first model-based estimation of groundwater availability across Africa, potentially serving as a catalyst to inspire further progress toward adopting more sustainable approaches to groundwater usage on the continent.

Coupling Simulation and Prediction of Sustainable Utilization of Water Resources in an Arid Inland River Basin under Climate Change

The arid endorheic basin of northwest China is characterized by rich land resources, water shortage, and a fragile ecological environment. The establishment of a credible coupling model of groundwater and surface water based on multi-source observation data is an effective means to study the change in basin water cycles and the sustainable utilization of water resources in the past and future. Based on the latest understanding of hydrogeological conditions, hydrology and water resource utilization data in the middle reaches of the Heihe River Basin (HRB), this paper constructs an up-to-date coupling model of surface water and groundwater to study the water balance change of the basin. The water resources data series under historical replay and CMIP5 climate model prediction are constructed to predict future changes in water resources. The study shows that, under the joint influence of natural conditions and human activities, the average annual recharge of groundwater in the study area from 1990 to 2020 is 17.98 × 108 m3/a, the average annual discharge is 18.62 × 108 m3/a, and the difference between recharge and discharge is −0.64 × 108 m3/a. The total groundwater storage is −19.99 × 108 m3, of which the groundwater storage from 1990 to 2001 was −17.52 × 108 m3 and from 2002 to 2020 was −2.47 × 108 m3. Abundant water from 2002 to 2020 in the basin significantly improved the loss of groundwater storage. Under the prediction of historical reappearance and the CMIP5 CNRM-CM5 model RCP4.5 and RCP8.5 pathways, the groundwater level of the Heihe River–Liyuanhe River inclined plain falls first because the HRB has just experienced a wet season and then rises according to future climate change. The groundwater level of the inclined plain east of the Heihe River and Yanchi basin decreases continuously because of the change in water cycle caused by human activities. The erosion accumulation plain is located in the groundwater discharge zone, and the water level is basically stable. Under the conditions of water resource development and utilization, the runoff of Zhengyixia hydrological station cannot meet the requirements of the “97 Water Dividing Plan” of the State Council in most years in the future, and the ecological and production water in the lower reaches of HRB cannot be effectively guaranteed. With the implementation of water-saving irrigation under the RCP4.5 and RCP8.5 scenarios, the runoff of Zhengyixia can meet the “97 Water Diversion Plan”. It is suggested to further improve the level of agricultural water savings in the middle reaches of the HRB and control the reasonable scale of cultivated land in order to reduce water consumption in the middle reaches of the HRB and implement sustainable utilization of water resources in the HRB.

Simulation of groundwater flow and seawater intrusion in response to climate change and human activities on the coastal aquifer of Gaza Strip, Palestine

This study has investigated the potential impact of human activities and climate change on the groundwater budget, water levels, and seawater intrusion in the coastal aquifer of the Gaza Strip (State of Palestine) over the next two decades. The impact of a proposed measure to use alternative freshwater provision from desalinated seawater on the future groundwater quantity and quality was also analyzed. Following extensive analysis of available observed data, a three-dimensional groundwater flow model, coupled with variable-density saltwater flow and transport components, was utilized for the investigations. Compared with the benchmark scenario (SC0), the climate change scenario (SC1) suggests that over the next two decades, an average annual aquifer recharge of 6.3 Mm3 can be expected, while the human activities scenario (SC2) indicates that the groundwater levels will decline at a rate of 0.09 m/year with expected urban area expansion. The combined human activities and climate change scenario (SC3) indicate severe groundwater storage depletion and seawater intrusion over the next two decades. The alternative freshwater provision scenario (SC4) indicates a strongly positive response in groundwater recovery (quantity and quality) over the next decades. The findings of this study emphasize strongly that the human activity impact, rather than climate change, is the driving force of groundwater depletion and that groundwater recovery interventions will be crucial in the future and should be implemented urgently.

Overexploitation assessment in an urban karst aquifer: The case of Sete Lagoas (MG), Brazil

Overexploitation of groundwater in urban karst aquifers can lead to negative consequences such as land subsidence, depletion of springs and lakes, and water pollution. It can also have indirect effects such as environmental, socio-economic, and political instability. In the municipality of Sete Lagoas, Brazil, the long-term effects of extensive groundwater extraction have been observed and studied over the years. This paper analyzes the response of the karst aquifer to urban, industrial, and climatological changes that may have contributed to changes in the aquifer over the last four decades. The results show that groundwater extraction has exceeded the average aquifer recharge since the year 2000. From the 1980s, the number of wells has steadily increased due to unplanned urban development, resulting in higher demand for groundwater. In the 2010s, pumping from tubular wells (7.39 × 107 m3/yr) exceeded the maximum recharge capacity of the aquifer (7.33 × 107 m3/yr). These wells are mainly concentrated in two areas: the central urban zone and the industrial sector. As a result, kilometer-long cones of depression have formed, changing the aquifer from confined to unconfined within these regions. According to the census data, about 67% of the wells remain unidentified. The average annual recharge to the aquifer is estimated to be 5.68 × 107 m3/yr, which accounts for 12% of the average annual rainfall in the region. Climatological trends indicate an incipient decrease in precipitation and an increase in temperature, suggesting a potential decrease in future aquifer recharge. In addition, only 17% of the area has high infiltration rates ranging from 35% to 75%. The current situation in Sete Lagoas is one of overexploitation of groundwater resources, which could be mitigated by localized reduction of groundwater consumption and implementation of effective management strategies to increase aquifer recharge.

Impact of land-use dynamics and climate change scenarios on Groundwater recharge in the case of Anger watershed, Ethiopia

An assessment of land use dynamics and climate variability impacts on hydrological processes is vital and a prerequisite for effective water resources management. This study aimed to quantify the effect of land-use changes and long-term climate variability on the Anger watershed's annual groundwater recharge, which covers a total drainage area of 7717 km2. The WetSpass (Water and Energy Transfer between Soil, Plants, and Atmosphere under quasi-Steady State) model was used to investigate the impact of land cover and climate variability on groundwater. The Mann–Kendall (MK) test was used to analyze the spatial variations and temporal trends of the climate variables in the watershed. Input data for the model, such as land use, hydro-meteorological data, soil texture, topography, and groundwater elevation parameters, were prepared in the form of gridded maps with a 30 m resolution. The model results indicate that land-use change and climate variability considerably impact distributed groundwater recharges. Groundwater recharge decreased with land use in 2000 and 2019, respectively, as compared to baseline land usage (1985). The study also demonstrates how the anticipated future combination of less precipitation and higher temperatures has a detrimental effect on the watershed's annual average groundwater recharge. Future rising temperatures and reduced precipitation are projected to result in an average annual groundwater recharge showing significant decreases in 2050, 2080, and 2110, respectively, according to scenario-based models. The result has provided valuable information on the management and response of groundwater recharge to climate and land-use changes, particularly for the Anger watershed and for the total country as well.

Climate Change Implication on Palestine: A Case Study Jenin Governorate

Climate change negatively affects sustainable development in Palestine, especially Jenin Gover-norate, which is the food basket for Palestine. This study identified climate change variables in Jenin Governorate for more than 100 years, especially temperatures and precipitation, derived from historical data to study the manifestations of climate change and its impact on water re-sources and the agricultural sector. The impact of climate change on groundwater wells is an un-derstatement. The majority of Jenin’s water wells, which number about 66 (including 22 agricul-tural wells), are located in the northeastern basin. By analyzing the data for the average annual total recharge of this basin, it was evident that the recharge had decreased from about 151 million cubic meters/year from 1976-1992 to about 134 million cubic meters/year during 1993-2009. (about 11.3%). This is because of the general solid decrease in rainfall in the Jenin area due to the effects of climate change. The decrease in recharge, coupled with increased groundwater pump-ing, has drained the reservoir stock and deteriorated the groundwater quality. The other source of water in Jenin Governorate is springs. Jenin Governorate has 42 streams largely used for small-scale agricultural and household needs. The research showed that the discharge of the springs increases from 2014 to 2020 (average discharge 0.48 MCM/yr.) compared to the period 2001 to 2011 (average discharge 0.48 MCM/yr.). years) due to the increase in the amounts of discharge from the springs and the start of relying on them more, as Jenin governorate is facing water scarcity recently. In the future, climate change will considerably impact water resources, altering surface and underground water supplies for residential and commercial purposes, irriga-tion, in-stream ecosystems, and aquatic leisure.

Water Balance Analysis of Hulun Lake, a Semi-Arid UNESCO Wetland, Using Multi-Source Data

Hulun Lake is the largest lake in northeastern China, and its basin is located in China and Mongolia. This research aims to analyze the dynamic changes in the water volume of Hulun Lake and to estimate the groundwater recharge of the lake during the past 60 years. Multi-source data were used, and water-level-data-interpolation extrapolation, water-balance equations, and other methods were applied. The proportion of the contribution of each component to the quantity of water in Hulun Lake during the last 60 years was accurately calculated. Evaporation loss was the main component in the water loss in Hulun Lake. In the last 60 years, the average annual runoff into the lake was about 1.202 billion m3, and it was the factor with the largest variation range and the leading factor affecting the changes in the quantity of water in Hulun Lake. There was groundwater recharge in Hulun Lake for a long period, and the average annual groundwater recharge was about 776 million m3 (excluding leakage). The contribution ratio of the river water, groundwater, and precipitation to the recharging of Hulun Lake was about 5:3:2. The changes in the quantity of water in Hulun Lake are affected by climate change and human activities in China and Mongolia, especially those in Mongolia.

Estimation of groundwater recharge variability using a GIS-based distributed water balance model in Makutupora basin, Tanzania

Groundwater recharge estimation in the Makutupora basin (1500 km2) is vital considering the potentiality of the basin to Dodoma city. This study aims to apply the WetSpass model to estimate the long-term average seasonal (dry and wet) and annual groundwater recharge for the Makutupora basin. Data required for this study were biophysical data (topography, land use, soil, slope, and depth to the groundwater) and long-term hydro-meteorological data (2000–2020). Data were collected by using both field visits and disk transfer from respective institutions and websites. Hydro-meteorological data were prepared for dry and wet seasons. Raster maps were prepared in ArcMap 10.4 using the Inverse Distance Weighting (IDW) interpolation technique followed by resampling into a 200 × 200 m grid size. Resampled raster maps were converted from raster to ASCII format suitable to input in the WetSpass model. The findings indicated that more recharge was dominating in the wet season ranging between 0 and 120 mm/year with a mean value of 24.65 mm (99%) while less recharge occurs in the dry season ranging between 0 and 4.35 mm/year with a mean value of 0.24 mm/year (1%) and annually recharge ranges between 0 and 120.88 mm/year with a mean value of 24.88 mm. Mean annual precipitation computed from data for twenty (20) years was 694 mm/year out of which recharge accounted for 3.6%, surface runoff 33.9% and evapotranspiration 62.5%. The groundwater table receives total average volumetric recharge of 37.3 million m3 annually from precipitation for the entire basin area. The model was employed to realize the area’s capacity for groundwater recharge to manage the water supply effectively, use it wisely, and plan for the future. Sustainable groundwater exploitation can be feasible only when there is knowledge of the rate at which groundwater is replenished annually. Therefore, the results of this study are useful in sustainable management plans, it may also be used as a benchmark for water supply authorities, policymakers and researchers to set proper protection measures and pumping policies.

Modifying the water table fluctuation method for calculating recharge in sloping aquifers

Study regionRobit Bata and Dengeshita watersheds, Upper Blue Nile basin, Ethiopia Study focusSustainable development of groundwater in the Ethiopian Highlands requires recharge measurements. The Water Table Fluctuation (WTF) method has been used to measure recharge. Lateral flow in sloping hillside aquifers violates the assumptions on which the original WTF method is based. We modified the original WTF method to include lateral flow controlled by gravity. New hydrological insightsPreviously it was shown that the sum of recharge over the travel time in a sloping aquifer is equal to the base flow. Since recharge cannot be measured directly, the recharge calculated with the modified WTF method was tested using baseflow measurement in two contrasting highland watersheds, Robit Bata and Dengeshita, where groundwater depth and streamflow data were monitored from 2015 to 2018. Baseflow was determined with the one-parameter digital filter technique. Predicted and observed monthly baseflow agreed well with R2 > 0.9 and RMSE < 20 mm during calibration and validation. Recharge in Robit Bata, in which the aquifer underlays 55% of the watershed, was 293 mm a−1 of 1378 mm a−1 precipitation. In Dengeshita, where the entire watershed has an aquifer, the average annual recharge was 525 mm a−1 of 1550 mm a−1. Our findings indicate that the modified WTF method is simple and practical for determining aquifer recharge for highlands and other sloping aquifers.