Average Groundwater Recharge Research Articles

The implications of climate change on freshwater resources in the arid and semiarid Mediterranean environments using hydrological modeling, GIS tools, and remote sensing.

Precipitation partitioning in arid and semiarid environments is not well understood due to scanty precipitation, its temporal distribution, and the lack/absence of adequate measurements of the hydrometeorological components. Simulation methods have the potential to bridge the data gap, thereby providing a window to estimate the water balance components. The present investigation evaluates the water balance components of a typical watershed situated in the southeastern Mediterranean for the period 1979 through 2019 using daily meteorological data and a grid spacing of 250 m. Generated runoff results were commensurate with corresponding values obtained using the SWAT model. Computed groundwater recharge is also compatible with recharge values calculated using the chloride mass balance method. Results show that average runoff and groundwater recharge for the entire period was ⁓24 mm a-1 and 19 mm a-1, giving a precipitation ratio of 9.5% and 7.5%, respectively. Substantial interannual variability in the water balance components was observed during the study period which reflected the significant precipitation fluctuations typifying the Eastern Mediterranean. Results show that the period extending from 1998/1999 through 2018/2019 witnessed an 18% drop in annual precipitation, while surface runoff and groundwater recharge experienced a reduction of ⁓34% and ⁓67%, respectively. Although groundwater recharge is a complex function of numerous meteorological and geological factors, the NDVI can provide an excellent indicator of groundwater recharge in marginal Mediterranean environments. This is highly beneficial in areas where climate records are scanty or absent. The presented results emphasize the significant impacts of global warming and aridification on the future availability of water resources in the semiarid marginal climates in the Eastern Mediterranean and point out clearly that water resources in this area will become scarcer, leading to multiple security threats at national and regional levels.

Improving the water table fluctuation method to estimate groundwater recharge below thick vadose zones

ABSTRACT The water table fluctuation (WTF) method is popular for groundwater recharge (GR) estimation, but its accuracy is challenged when applied in areas with thick vadose zones because of the signal lag and attenuation with depth and uncertainties from barometric pressure effect and lateral flow. Improvement of the WTF method used the linear regression method and Darcy’s law, and has been assessed to give satisfactory results. In particular, the improved method presented lower GR (20–34%) relative to the conventional method. GR decreased from the centre to the edge of the tableland. The regional average GR was 63–81 mm year−1, equivalent to 11–14% of annual average rainfall. Lag times between recharge and rainfall ranged from 1 to 9 months. Rainfall and vegetation dominated the spatiotemporal variability of GR. Our study provides reference and technical support for GR estimation with the WTF method in regions with a thick vadose zone.

High-resolution long-term average groundwater recharge in Africa estimated using random forest regression and residual interpolation

High-resolution long-term average groundwater recharge in Africa estimated using random forest regression and residual interpolation

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.

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.

Assessment of Groundwater Recharge Using WetSpass-M and MODFLOW Coupling in Jedeb Watershed, Upper Blue Nile Basin, Ethiopia

Currently, the demand for water is rising, and as a result, the groundwater is declining. Water supplies are not sufficient for agricultural productivity, environmental preservation, or ecosystem services, resulting in an unbalanced water budget in the basin. The goal of this paper is to assess the groundwater recharge in the Jedeb sub-basin using WetSpass-MODFLOW coupling. A spatially distributed water balance model is developed to simulate long-term average recharge depending on land cover, soil texture, topography, and hydro meteorological parameters. The groundwater model is iteratively connected to the recharge model in order to simulate recharge. This means that the depth of the groundwater affects the recharge estimate and vice versa. The average yearly evapotranspiration, surface runoff, and groundwater recharge were determined using WetSpass-M to be 574, 898, and 99 mm, respectively. Groundwater recharge accounted for 6.3% of precipitation, while actual evapotranspiration and surface runoff accounted for 36.4% and 57% of precipitation, respectively. In such seasonal variations, the groundwater level in the Jedeb Sub-basin was studied under various stress conditions (dry season, wet season, and annually). The groundwater level distribution varied from 2,052.3 to 3,063.06 m in the summer stress period (recharge). While in the winter stress period (recharge), the groundwater level varied from 2,051.41 to 3,061.92 m, and the groundwater level due to the annual stress period (recharge) varied from 2,053.76 to 3,064.5 m. With a correlation coefficient of .89, which is an acceptable fit between the simulated and observed heads in steady state for all stress periods (summer, winter, and annual recharge). The contribution of this study could be used as baseline information for regional water resource experts, policymakers, and researchers for further investigation.

Hydrological Analysis Before and After Embankment-Raising Project of Agricultural Reservoir Watershed: A Case Study of Suyang Reservoir

We selected the SWAT hydrological model to analyze the hydrological changes before and after an embankment-raising project in agricultural reservoirs. The model was calibrated and validated from 2015 to 2016 using discharge data from the Songsan gauge station, which serves as a watershed outlet that includes the Suyang Reservoir. The dam height of Suyang Reservoir was raised from 13.5 m to 15.1 m, which resulted in a total storage capacity increase from 7.472 million cubic meters to 11.926 million cubic meters. The calibrated model demonstrates an efficiency of 0.9. Scenarios for pre- (2001-2012) and post-embankment raising (2014-2016) were simulated, and the results for various hydrological components (precipitation, runoff, infiltration, evapotranspiration, percolation, soil moisture, groundwater evaporation, and groundwater recharge) were summarized. The model results revealed average precipitation, runoff, infiltration, evapotranspiration, and groundwater recharge for the pre-embankment raising period (2001-2012) as 1,479.3 mm, 864.1 mm, 550.8 mm, 584.2 mm, and 165.0 mm, respectively. For the post-embankment raising period (2014-2016), the simulated values were 1,290.4 mm, 678.0 mm, 494.0 mm, 587.9 mm, and 145.9 mm, respectively. Below-average precipitation during the post-embankment raising period did not have a significant impact on the operation of the agricultural reservoir. The increased reservoir capacity through the embankment-raising project suggests the potential for additional water supply in the face of future water shortages and abnormal drought conditions. Additional research, including the determination of an appropriate water storage rate, will be necessary through long-term investigations and analyses, and climate change scenarios should be incorporated.

Modelling groundwater recharge, actual evaporation, and transpiration in semi-arid sites of the Lake Chad basin: the role of soil and vegetation in groundwater recharge

Abstract. The Lake Chad basin, located in the centre of northern Africa, is characterized by strong climate seasonality with a pronounced short annual precipitation period and high potential evapotranspiration. Groundwater is an essential source for drinking-water supply, as well as for agriculture and groundwater-related ecosystems. Thus, assessment of groundwater recharge is very important although also difficult because of the strong effects of evaporation and transpiration, as well as the limited available data. A simple, generalized approach, which requires only limited field data, freely available remote sensing data, and well-established concepts and models, is tested for assessing groundwater recharge in the southern part of the basin. This work uses the FAO dual-Kc concept to estimate E and T coefficients at six locations that differ in soil texture, climate, and vegetation conditions. Measured values of soil water content and chloride concentrations along vertical soil profiles together with different scenarios for E and T partitioning and a Bayesian calibration approach are used to numerically simulate water flow and chloride transport using Hydrus-1D. Average groundwater recharge rates and the associated model uncertainty at the six locations are assessed for the 2003–2016 time period. Annual groundwater recharge varies between 6 and 93 mm and depends strongly on soil texture and related water retention and on vegetation. Interannual variability of groundwater recharge is generally greater than the uncertainty of the simulated groundwater recharge.

Groundwater Recharge Assessment for Small Karstic Catchment Basins with Different Extents of Anthropogenic Development

Climate change and anthropogenic development considerably influence groundwater resource distribution and conditions. Catchment basin groundwater recharge—discharge computation reliability is needed for effective groundwater management policy formulation and implementation and also for resolving environmental challenges in such a watershed. This paper compares groundwater recharge patterns between urbanized and nearly natural small catchment basins of Israel’s Western Mountain Aquifer (WMA). The correlation between precipitation volumes and surface runoff shows that surface runoff volume constitutes 3–4% of the precipitation volume in the Natuf catchment and 1–2% in the Te’enim catchment. These assessments reflect the differences in the land use, outcrop lithology, topography and hydrodynamic properties of the WMA within the model basins. A groundwater recharge assessment based on water balance and water table fluctuation methods was performed for the mountainous karstic Te’enim and Natuf catchment basins for all the available data from 2000 to 2020. The water balance method provided reliable estimates. The groundwater recharge assessment considered land use classification and climate changes during this period. The average multiannual groundwater recharge values for the 2000–2021 period varied from 17.6 × 106–24.8 × 106 m3 to 24.5–29.2 × 106 m3 for the Te’enim and Natuf catchment basins, respectively. For the relatively dry period of the 2013/2014–2017/2018 hydrological years when detailed measurements of the surface runoff were available, the corresponding groundwater recharge volumes were 17.6 × 106 m3 and 24.5 × 106 m3. The corresponding local groundwater recharge coefficients constitute 0.46–0.57 for the mostly agricultural Te’enim basin and 0.29–0.32 for the urbanized Natuf basin. A significant difference in the groundwater recharge coefficients between the studied catchments is caused mostly by the differences in land use. It is suggested that applying such a groundwater recharge estimation for small hydrological sub-basins can improve one’s understanding of the groundwater recharge distribution within a major basin, enabling the application of an accurate regional hydrogeological model that may be extrapolated to other similar regions.

Estimating Land Use Change Effects on Groundwater Recharge in Nadi and Kabinburi, Thailand

The effect of land use change on groundwater recharge in Nadi and Kabinburi Districts, Prachinburi Province, Thailand was studied by forecasting land use change using the CLUE model and estimating groundwater recharge using the H08 model. The results suggested that compared to the current average groundwater recharge, the groundwater recharge estimates from scenario 1 (changing the miscellaneous areas of mostly wasteland to mixed perennial areas) and scenario 2 (predicting the land use scenario for the next 10 years based on trends of land use change from the past to the present) were greater by 1.46 and 2.25%, respectively. In scenario 1, the increase in forest and mixed perennial areas increased the groundwater recharge by helping to slow down the surface runoff and, thus, increased the chances of water seepage into the soil. However, increasing the perennial area or turning wasteland into mixed perennial area (scenario 1), resulted in an increase in the groundwater recharge that was similar to the results from simulating future land use scenarios in the next 10 years (scenario 2). Therefore, to increase the efficiency of groundwater management and drought relief, the relevant agencies should adopt appropriate land use planning, be encouraged to plant perennials or support mixed farming on wasteland, restore degraded forest areas, and improve the management of water use concurrently.

Bridging the data gap: using remote sensing and open-access data for assessing sustainable groundwater use in Kumasi, Ghana

Abstract Groundwater use has significantly increased in the rapidly urbanising city of Kumasi, Ghana. But there is a lack of understanding of whether the groundwater system can sustain the growing demand in the future amidst climate change and rapid urbanisation. Using remote sensing datasets and a water balance approach, this study estimated the groundwater recharge and assessed how urbanisation has affected its groundwater sustainability. Sustainability is investigated by comparing multi-annual groundwater withdrawals to long-term average annual replenishment. Results show that while groundwater recharge has decreased by 80% from 1986 to 2020, mainly due to substantial (63%) loss of permeable land, groundwater consumption has seen a six-fold increase. Groundwater consumption in 2020 exceeded the long-term average groundwater recharge by 2.2Mm3, suggesting that the current groundwater use trends are unsustainable for future groundwater availability. Under a ‘business-as-usual’ scenario, a four-fold increase in groundwater consumption is predicted by 2050 while climate change and land-cover changes may reduce groundwater recharge by 10% and 55% respectively. Practical measures such as promoting artificial groundwater replenishment approaches, adopting low-impact development and instituting demand management measures must be implemented in the Metropolis. This should be informed by further studies to ascertain the exact condition of the groundwater.

Quantification of Mountainous Hydrological Processes in the Aktash River Watershed of Uzbekistan, Central Asia, over the Past Two Decades

Estimation of hydrological processes is critical to water resource management, water supply planning, ecological protection, and climate change impact assessment. Mountains in Central Asia are the major source of water for rivers and agricultural practices. The disturbance of mountain forests in the region has altered the hydrological processes and accelerated soil erosion, mudflow, landslides, and flooding. We used the SWAT (Soil and Water Assessment Tool) model calibrated and validated with remote sensing data to quantify the mountainous hydrological processes in the Aktash River watershed (ARW) of Uzbekistan, Central Asia. Simulations showed that the daily surface runoff and streamflow closely responded to daily precipitation. Groundwater discharge reached its maximum in winter because of snowmelt. The wet months were from July to December, and the dry months were from January to June. The magnitudes of the seasonal hydrological processes were in the following order: fall > summer > winter > spring for precipitation and surface runoff; summer > spring > fall > winter for evapotranspiration (ET); winter > spring > fall > summer for snowmelt; fall > winter > summer > spring for water yield and streamflow; and winter > fall > spring > summer for groundwater discharge. The Mann–Kendall statistical test revealed a significant increasing trend for the annual precipitation (τ = 0.45, p < 0.01) and surface runoff (τ = 0.41, p < 0.02) over the past 17 years from 2003 to 2019. Compared to rangeland, forested land decreased monthly and annual average surface runoff by 20%, and increased monthly and annual average groundwater recharge by about 5%. Agricultural land had much higher unit-area values (mm/km2/y) of ET, groundwater recharge, and water yield than those of urban, forest, and range lands. Our research findings provide useful information to farmers, foresters, and decision makers for better water resource management in the ARW, Central Asia, and other mountain watersheds with similar conditions.

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.

Managing climate change impacts on the Western Mountain Aquifer: Implications for Mediterranean karst groundwater resources

Many studies highlight the decrease in precipitation due to climate change in the Mediterranean region, making it a prominent hotspot. This study examines the combined impacts of climate change and three groundwater demand scenarios on the water resources of the Western Mountain Aquifer (WMA) in Israel and the West Bank. While commonly used methods for quantifying groundwater recharge and water resources rely on regression models, it is important to acknowledge their limitations when assessing climate change impacts. Regression models and other data-driven approaches are effective within observed variability but may lack predictive power when extrapolated to conditions beyond historical fluctuations. A comprehensive assessment requires distributed process-based numerical models incorporating a broader range of relevant physical flow processes and, ideally, ensemble model projections. In this study, we simulate the dynamics of dual-domain infiltration and precipitation partitioning using a HydroGeoSphere (HGS) model for variably saturated water flow coupled to a soil-epikarst water balance model in the WMA. The model input includes downscaled high-resolution climate projections until 2070 based on the IPCC RCP4.5 scenario. The results reveal a 5% to 10% decrease in long-term average groundwater recharge compared to a 30% reduction in average precipitation. The heterogeneity of karstic flow and increased intensity of individual rainfall events contribute to this mitigated impact on groundwater recharge, underscoring the importance of spatiotemporally resolved climate models with daily precipitation data. However, despite the moderate decrease in recharge, the study highlights the increasing length and severity of consecutive drought years with low recharge values. It emphasizes the need to adjust current management practices to climate change, as freshwater demand is expected to rise during these periods. Additionally, the study examines the emergence of hydrogeological droughts and their propagation from the surface to the groundwater. The results suggest that the 48-month standardized precipitation index (SPI-48) is a suitable indicator for hydrogeological drought emergence due to reduced groundwater recharge.

Climate elasticity assessment on groundwater recharge to the Edwards Balcones Fault Zone Aquifer, United States

AbstractThis study presents a comprehensive analysis of the characteristics of precipitation, temperature, and groundwater recharge in the recharge zone of the nine basins of the San Antonio segment of the Edwards Balcones Fault Zone Aquifer, which is one of the major groundwater systems in the United States and serves as primary water sources for approximately 1.7 million people in south‐central Texas. Datasets of monthly precipitation and average temperature (1895–2019) and groundwater recharge (1934–2019) are used to examine the decadal variability in precipitation, temperature, and groundwater recharge on the annual scale with a normalized 20‐year moving average of variance. Climate elasticity (precipitation and potential evapotranspiration) of groundwater recharge is estimated to evaluate impacts of climate change on groundwater recharge. The results of this study show that precipitation and temperature variability exhibit decadal cyclic patterns. Elasticity analysis of groundwater recharge indicates that a 1% change in annual precipitation may result in 2%, with a likely range of 0.15%–2.8%, change in groundwater recharge, and a 1% change in annual potential evapotranspiration may lead to −3.3% change in groundwater recharge with a likely range of −8.9% to 4% in the study area. This study suggests that climate elasticity of groundwater recharge may provide an alternative means for evaluating climate impacts on groundwater recharge to an aquifer.

Инфилтрационно подхранване и ресурси на подземните води в басейна на р. Тунджа, ЮИ България

This article presents the assessment results of the long-term annual average groundwater recharge for the territory of the Tundzha River catchment area. In order to assess those results, a GIS-method has been applied based on spatial analysis of the slope of the relief, soil cover and aquifer properties. A series of maps is presented and a quantitative analysis of the results obtained is carried out. The mean annual groundwater recharge ranges from 4 to 483 mm, or about 55 mm on average for the catchment area. Additional calculations have been made for water management purposes. For individual groundwater bodies that fall into the catchment area of the Tundzha River (managed primarily by the East Aegean River Basin Directorate) both groundwater recharge and their natural groundwater resources were assessed (based on the outcrop areas of the respective bodies).

Groundwater recharge estimation under changing climate and land use scenarios in a data-scarce Bahi (Manyoni) catchment in Internal Drainage Basin (IDB), Tanzania using Soil and Water Assessment Tool (SWAT)

Spatio-temporal studies of groundwater recharge establish a groundwork for comprehending the effects of climate and land use change on groundwater resources, particularly in areas where groundwater is a primary source of water such as the Internal Drainage Basin (IDB), Tanzania. Therefore, quantification of groundwater recharge for years the 2050s and 2080s was executed using the SWAT in Bahi (Manyoni) Catchment (BMC) in IDB. Shared Socioeconomic Pathways (SSPs) climate scenarios particularly SSP245 as medium emission and SSP585 as high emission scenario were used. Monthly calibration and validation of the SWAT model were performed by using streamflow data from a gauged sub-catchment within BMC. Obtained Nash-Sutcliffe Efficiency (NSE) for the calibration period from 1971 to 1982 was 0.79 and for the validation period from 1983 to 1990 was 0.69. Later, performed another validation using actual evapotranspiration in an ungauged BMC achieved NSE of 0.59. The findings from calibrated model depicted, under the impact of climate change alone, it was estimated that there will be a slight increase in overall annual average groundwater recharge of 3.05 mm/y under SSP245 and to 5.12 mm/y under SSP585 in year 2050s whereas under collective impact of climate and LULC change an increase of 2.31 mm/y under SSP245 and of 3.98 mm/y under SSP585 in year 2080s from a baseline of 4.5 mm/y in 1980s. This indicates the impact of LULC alone to be trivial. In the steep slope areas, the catchment with 15% reduced rainfall will experience lower recharge of up to 24% whereas gentle slope areas with a 25% increase in rainfall will experience a recharge of up to 123% compared to the baseline period. Established groundwater recharge zones give imperative information to IDB managers in relation to water management plans to optimize future groundwater recharge.

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.

Study on groundwater recharge based on chloride mass balance and hydrochemistry in the irrigated agricultural area, North China Plain

In the North China Plain, water shortage seriously restricts economic development, and agricultural irrigation depends heavily on groundwater extraction. Irrigation water and precipitation may directly recharge groundwater in the irrigated agricultural region. Therefore, calculating the recharge of precipitation and irrigation to groundwater is essential for the sustainable utilization of water resources. Furthermore, determining the transformation relationship of precipitation-soil water-groundwater is helpful to understand the hydrological cycle process better. The average groundwater recharge calculated by the chloride mass balance method is between 66 and 144 mm/year, accounting for only 7–17% of the total precipitation and irrigation water. The hydrogen (2H) and oxygen (18O) isotopes reveal that precipitation only affects soil water in topsoil, and soil water in deep soil is recharged upward by groundwater. The hydrochemical composition of soil water shows high concentrations of salt in unsaturated zones. Infiltration water dissolves salt through the unsaturated zone and carries them into the shallow groundwater, causing the deterioration of shallow groundwater quality. These results contribute to the effective management of groundwater resources and the control of agricultural pollution in groundwater.