Estimating Groundwater Recharge Research Articles

A comparison of methods to estimate groundwater recharge from bare soil based on data observed by a large‐scale lysimeter

AbstractEffectively estimating groundwater recharge is critical to manage water resources, especially in arid and semi‐arid regions as impacted by intensive human activities and climate changes. Rare insights have been gained into groundwater recharge since direct observation is hard to carry out. Although several methods are currently available to estimate groundwater recharge, the estimated results may cover noticeable bias. The behaviours of different methods based on different conceptual frameworks and exhibiting different levels of complexity should be examined to estimate actual groundwater recharge. This study aims to assess the performance of four common methods to estimate groundwater recharge. For this end, large‐scale lysimeters equipped with soil water content sensors and water table sensors were set up at a research site established in Guanzhong Basin of China. The data achieved by 1‐year observation were employed to compare four estimation methods. As revealed from the results, the following findings are drawn. (a) Groundwater level fluctuation (GLF) method is simple, whereas its accuracy is determined by specific yield, and adopting a water balance method to estimate specific yield can considerably enhance the accuracy of GLF. (b) The calibrated numerical model can obtain the optimal result compared with the other methods, whereas long‐term observation data are required for parameter calibration. (c) In the water balance method, the maximum entropy production (MEP) model and a practical method (estimating evaporation between two rainfall events) were used to calculate evaporation. As indicated by the results, water balance method combined with MEP is capable of obtaining more reliable results of groundwater recharge compared with the practical method. (d) With an analytical model based on linearized Richards' equation, accurate results can be achieved. What is more, the analytical model only needs the measurement of soil moisture near the surface. The limitation of this method is that it is difficult to determine the maximal water flux. The mentioned findings are of critical implications to the management and sustainable development of groundwater.

Evaluation of vertical groundwater flux from borehole temperatures: a case study in the Leizhou Peninsula, South China

A least-square solver is presented for groundwater flux estimation using the one-dimensional conduction–advection equation, which was numerically solved using the MacCormack scheme. This approach was utilized to estimate groundwater fluxes from observed borehole temperatures under conditions of surface warming in both rural and urban areas in Leizhou Peninsula, China. The estimated groundwater recharge rate is 0.423 m/year, while the discharge rate is 0.269 m/year. The groundwater recharge rates were obtained in the north part of the study area, and the discharge locations were on Nansan, Donghai and Luzhou Islands, which fit favorably with the regional groundwater flow pattern. Relatively high correlations and low root mean square errors were detected between observed and computed borehole temperature–depth profiles, indicating the estimation is reasonable. The misfit between the observed and computed data might be associated with the uneven distribution of ground surface temperature (GST) and vertical soil heterogeneity. The urban heat island effect contributes an increment of 0.006 °C per year to the GST in the study area, which induces a 0.96 °C higher subsurface temperature in both recharge and discharge areas. The utilization of surface air temperature (SAT) as the upper boundary might underestimate groundwater fluxes, which might lead to inaccurate information for regional groundwater resource management.

Derivation mathematical equations to estimate water surplus and groundwater recharge in Iraq

Climate and hydrological conditions in any hydrological basin are multi-combined reflection of natural factors of morphology and soil nature, as well as the changing in climate factors that affect directly the hydrological cycle. The water balance equation for any natural area or water body indicates the relative values of inflow, outflow, and change in water storage for the area or water body. Estimation of water surplus and natural groundwater recharge in Iraq depending on water balance equation and meteorological data was the aim of this research. Corrected potential evapotranspiration were compared with annual and monthly rainfall in (32) meteorological stations to obtain actual evapotranspiration using water balance equation. Water surplus was divided into runoff and natural groundwater recharge where runoff coefficient method was used to estimate runoff. The obtained mathematical relationship between rainfall with both water surplus and actual evapotranspiration can be used to estimate these two parameters directly from rainfall. The results indicate that water surplus increased toward northeast direction of Iraq, while the minimum values of runoff and groundwater recharge located in western desert of Iraq. The climate conditions of desert were the major influence on reducing rainfall and rising temperature resulting decreasing water surplus, runoff, and groundwater recharge.

Recharge–Discharge Relations of Groundwater in Volcanic Terrain of Semi-Humid Tropical Highlands of Ethiopia: The Case of Infranz Springs, in the Upper Blue Nile

The major springs in the Infranz catchment are a significant source of water for Bahir Dar City and nearby villages, while sustaining the Infranz River and the downstream wetlands. The aim of the research was to understand the hydrogeological conditions of these high-discharge springs and the recharge–discharge relations in the Infranz catchment. The Infranz catchment is covered by highly pervious and young quaternary volcanic rocks, consisting of blocky, fractured, and strongly vesicular scoriaceous basalt. At the surface, these rocks crop out as lineaments forming ridges, delimiting closed depressions in which water accumulates during the rainy season without causing surface runoff. Geology and geomorphology thus combine to produce very favorable conditions for groundwater recharge. Three groundwater recharge methods were applied to estimate groundwater recharge and the results were compared. Groundwater recharge was calculated to be 30% to 51% of rainfall. Rapid replenishment raises the groundwater level during the rainfall period, followed by a rapid decline during the dry season. Shallow local flow paths discharge at seasonal springs and streams, while more regional and deeper flow systems downstream sustain the high-discharge springs and perennial Infranz River. The uptake of 75% of spring water for the water supply of Bahir Dar City, local extraction for domestic and small-scale irrigation use from springs, rivers and hand-dug wells, encroaching farming, and overgrazing are exacerbating wetland degradation.

Simple Methodology for Estimating the Groundwater Recharge Potential of Rural Ponds and Lakes Using Remote Sensing and GIS Techniques: a Spatiotemporal Case Study of Roorkee Tehsil, India

Groundwater resources are depleting at an alarming rate all over the world. Therefore, ensuring water security is the foremost priority of every nation. This paper presents a simple methodology to estimate groundwater recharge from rural ponds and to study the impact of climate change and urbanization on the recharge potential. It was found that built-up in the study area has increased by 51% since 2002 as a consequent of which, the total area occupied by ponds has decreased by 11%. This has resulted in a decrease in the recharge volume from these ponds by 14.74%. Thus, there is an urgent need to rejuvenate and maintain natural ponds and lakes, which is much more economical than constructing artificial percolation tanks and injection wells as discussed in the report. This study will also help various Government initiatives of rejuvenation of natural ponds and lakes in identifying those ponds which need to be revived based on their size, amount of surface runoff stored by the ponds and the volume of groundwater recharge through seepage from the bed of ponds.

The Sensitivity of Groundwater Recharge to the Rock Pore Connectivity Parameter in the Vadose Zone

Data on groundwater recharge is necessary for solving different classes of hydrogeological problems. One of the recharge estimation methods is flow simulation in the vadose zone. Soil hydraulic parameters are used to estimate the recharge by flow in the vadose zone. One of these hydraulic parameters is the pore connectivity l. The estimated recharge sensitivity to the pore connectivity, especially under humid climate conditions, has not been studied thoroughly. In this study, the experimental values of soil hydraulic parameters of samples from two different sites with various landscape conditions and vadose zone structure (forest conditions on sand and field conditions on loam) have been used to estimate the groundwater recharge. The recharge was also estimated at l = 0.5 and at reported values of the l parameter for a certain type of sediment. According to the calculation results, the use of a fixed value of l = 0.5 leads to a significant overestimation of recharge under both forest and field conditions, which emphasizes the importance of experimental determinations of soil hydraulic parameters for the groundwater recharge estimation. According to the data from an analysis on water balance components, the increase in the estimated recharge with an increase in l is mainly related to a decrease in a top soil evaporation.

Evaluation of groundwater recharge estimation methods in a watershed in the Brazilian Savannah

The Brazilian Savannah Biome is strategic for Brazilian agriculture and for maintaining Brazil's hydrological balance, contributing to river flows from eight of the twelve Brazilian hydrographic regions. In recent years, there has been a continuous growth of irrigated agriculture, the main activity that uses the water resource, and the emergence of conflicts over water use. Thus, to improve water resource management in the Brazilian Savannah, it is important to better understand groundwater recharge rates to determine the magnitude of the sustainable groundwater resource in the region. The study aimed to evaluate groundwater recharge estimation methods in a watershed located in the Brazilian Savannah region. For this, recharge rates were calculated for the period from October 2009 to September 2011 using the methods of baseflow separation, water table fluctuation, and a sequential water balance (BALSEQ). The recharge rates estimated by the baseflow separation, and water table fluctuation methods were, respectively, 23.7% and 26.6% of the total rainfall of 1753.8 mm in the watershed. Using the BALSEQ water balance method, the potential recharge for the period was estimated to be 31.5% of annual average precipitation. The recharge estimates calculated by the methods were consistent with those observed in other agricultural watersheds in the Brazilian Savannah Biome. Also, the evaluated methods can be used as a tool by water resource managers for the rational use of groundwater.

Analysis and quantification of groundwater recession characteristics in regolith-bedrock aquifers: a case study in the mid- and upper-Choshuei river basin in central Taiwan

Investigating the groundwater recession characteristics and its relation with geological conditions is of critical importance to the estimation of groundwater recharge in regolith-bedrock aquifers, which commonly occur in the mountainous areas of Taiwan. This paper examines the role of geological and hydrogeological factors in controlling rainfall-induced recharge processes. Groundwater and rainfall data were compiled from 29 monitoring wells and rainfall stations situated in the mid- and upper-Choshuei river basin in central Taiwan. In light of analyzing the outcome of the groundwater-level response to rainfall, the relation between the effective rainfall and groundwater-level fluctuation tends to be positive, and rainfall events with high intensity firmly control the groundwater recharge process in Taiwan mountainous areas. Permeable geological units likely dominate the groundwater-level variations. Besides, recession rates in the vertical direction varying with geological conditions were obviously found in each well site. To improve the efficiency of the water table fluctuation (WTF) method on extrapolating recession rates, two rating systems for evaluating hydraulic properties of regolith and fractured bedrock, respectively, were proposed and applied to develop the effective techniques linked to the quantification of recession characteristics varying with depths for each well. By regression analysis, the dependence of the hydraulic property rating system on the recession rate was performed, and the derived regression equation for each well can be used to estimate the recession rate with depths. Finally, the recharge estimation with the above techniques in Taiwan mountainous areas was established, and the present method of estimating recharge was compared with the existing method. The difference between the two methods was obviously found. Thus, recharge estimation in mountainous areas should take account of complex geological conditions.

On the sensitivity of modelled groundwater recharge estimates to rain gauge network scale

Rainfall is often the largest component of the water budget and even a small uncertainty percentage may lead to challenges for accurately estimating groundwater recharge as a calculated residual within a water budget approach. Watersheds are a common scale for water budget assessment, and rainfall monitoring networks typically have widely spaced gauges that are frequently outside the watershed of interest. The effects of rainfall spatial variability and uncertainty on groundwater recharge estimates have received little attention and may influence water budget-derived recharge estimations. In the present study, the influence of spatial density in rainfall measurement on the numerical estimation of groundwater recharge was investigated through a series of modelling scenarios utilizing field data obtained from progressively denser rain gauge networks associated with a typical watershed in southern Ontario. The uncertainty of the recharge component of the water budget was used as a metric to aid interpretation of results. The scenarios employed networks composed of: 1) one nearby national weather station (within 3 km), 2) a regional network of six stations (within 30 km), and 3) a local network of six stations, five of which were within the selected watershed. A coupled and fully distributed hydrologic model (MIKE SHE) was used in the scenario analysis and applied to the Alder Creek watershed on the Waterloo Moraine near Kitchener-Waterloo, Ontario. Rainfall showed poor spatial correlation, even at the daily time scale. Average annual results over a three-year period showed that recharge rates varied up to 140 mm per year (~40% of previously estimated annual recharge) among scenarios, with differences between scenarios greater than the water budget uncertainty during one of the years. These findings suggest that the availability of local rainfall measurements has the potential to influence the calibration of transient watershed hydrogeological models.

Estimation of groundwater recharge in savannah aquifers along a precipitation gradient using chloride mass balance method and environmental isotopes, Namibia

The quantification of groundwater resources is essential especially in water scarce countries like Namibia. The chloride mass balance (CMB) method and isotopic composition were used in determining groundwater recharge along a precipitation gradient at three sites, namely: Tsumeb (600 mm/a precipitation); Waterberg (450 mm/a precipitation) and Kuzikus/Ebenhaezer (240 mm/a precipitation). Groundwater and rainwater were collected from year 2016–2017. Rainwater was collected monthly while groundwater was collected before, during and after rainy seasons. Rainwater isotopic values for δ18O and δ2H range from −10.70 to 6.10‰ and from −72.7 to 42.1‰ respectively. Groundwater isotopic values for δ18O range from −9.84 to −5.35‰ for Tsumeb; from −10.85 to −8.60‰ for Waterberg and from −8.24 to −1.56‰ for Kuzikus/Ebenhaezer, while that for δ2H range from −65.6 to −46.7‰ for Tsumeb; −69.4 to −61.2‰ for Waterberg and −54.2 to −22.7‰ for Kuzikus/Ebenhaezer. Rainwater scatters along the GMWL. Rainwater collected in January, February and March are more depleted in heavy isotopes than those in November, December, April and May. Waterberg groundwater plots on the GMWL which indicates absence of evaporation. Tsumeb groundwater plots on/close to the GMWL with an exception of groundwater from the karst Lake Otjikoto which is showing evaporation. Groundwater from Kuzikus/Ebenhaezer shows an evaporation effect, probably evaporation occurs during infiltration since it is observed in all sampling seasons. All groundwater from three sites plot in the same area with rainwater depleted in stable isotopic values, which could indicates that recharge only take place during January, February and March. CMB method revealed that Waterberg has the highest recharge rate ranging between 39.1 mm/a and 51.1 mm/a (8.7% – 11.4% of annual precipitation), Tsumeb with rates ranging from 21.1 mm/a to 48.5 mm/a (3.5% – 8.1% of annual precipitation), and lastly Kuzikus/Ebenhaezer from 3.2 mm/a to 17.5 mm/a (1.4% – 7.3% of annual precipitation). High recharge rates in Waterberg could be related to fast infiltration and absence of evaporation as indicated by the isotopic ratios. Differences in recharge rates cannot only be attributed to the precipitation gradient but also to the evaporation rates and the presence of preferential flow paths. Recharge rates estimated for these three sites can be used in managing the savannah aquifers especially at Kuzikus/Ebenhaezer where evaporation effect is observed that one can consider rain harvesting.

Estimation groundwater total recharge and discharge using GIS-integrated water level fluctuation method: a case study from the Alaşehir alluvial aquifer Western Anatolia, Turkey

The estimation of groundwater recharge is an essential process for hydrogeological study. Realistic determination approach is crucial for assessing groundwater potential in an aquifer system and estimating of groundwater levels and/or changes in dry periods. Based on these matters, we employ a GIS-integrated groundwater level fluctuation method to determine the groundwater recharge for a hydrological period in the Alasehir alluvial aquifer (W. Anatolia). The method basically takes into account both increasing and decreasing of the groundwater levels due to the recharge and discharge mechanisms in the aquifer. In this study, 16 pumping and monitoring wells were drilled with a total depth of 1300 m, and water level data loggers were installed into the monitoring wells to determine the groundwater level changes. The spatial distribution of the monthly groundwater level change map was multiplied by the aquifer storage distribution map and then the accurate water volume is calculated by using the 3-D spatial analysis. According to our evaluation in the aquifer, positive volume change of the groundwater is 187 hm3 in a year, which is considered as a recharge value of groundwater. It is concluded that the GIS-integrated water table fluctuation method gave rise to estimate the total recharge amount of the groundwater in the Alasehir aquifer. The total groundwater recharge indicates that total inflow in the aquifer from precipitation, leakage from surface water and irrigation waters. It can be stated that the recharge estimation of groundwater in a surficial aquifer, like the Alasehir aquifer, is fairly easy using the GIS-integrated water table fluctuation method.

Diffuse groundwater recharge estimation confronting hydrological modelling uncertainty

Diffuse recharge is vital in determining the availability of renewable groundwater. Estimating diffuse recharge, however, is a great challenge plagued with uncertainty due to limitations in direct observation and process understanding. Hydrological model is functional for diffuse recharge estimation at catchment scale. It can be used independently or in combination with flow recession analysis to estimate recharge but it is accompanied with uncertainties owing to model structures and parameterization schemes. Confronting the uncertainties in hydrological modelling, in this paper, we used three models (GR4J, SIMHYD and IHACRES) together with nine parameterization schemes to investigate the effectiveness and uncertainties in the estimates of diffuse recharge for unregulated headwater catchments. The parameterization schemes were configured by three objective functions and three calibration periods conditioned on climate. It was found that the capability of hydrological model in yielding more reasonable groundwater recharge estimates largely depended on the objective function used and the calibration period configured. Model calibrated using inverse NSE (NSEInv) was judged to be more likely to yield better recharge estimates. The uncertainties due to the choice of parameterization scheme were found to be comparable with those from model structures. The use of different models, objective functions and calibration periods allowed reflection on the level of uncertainties one can minimally expect in estimating catchment scale recharge.

Chronology and characteristics of groundwater along the United Arab Emirates-Oman arid region: a guide for regional sustainability

Estimating groundwater recharge rate is essential for water sustainability of the arid region of the United Arab Emirates that receives most groundwater recharge from the bordering mountain ranges in Oman. Analyses of major ions, stable isotopes (δ2H and δ18O) and the radioactive isotope (14C) and the HydroGeoSphere (HGS) three-dimensional numerical model approach were applied here to investigate groundwater residence time in the aquifers and the recharge rates in the region. Estimate of groundwater recharge ranges from 1.03 to 36.6 mm/year with an average of 5.8 mm/year based on groundwater ages and ranges from 0.23 to 35.3 mm/year with an average of 6.5 mm/year based on HGS modelling. The data provide vital information for making sustainable plans for natural water resources with expected future reduction in rainfall in this region and other arid areas of the Middle East and the world.

Estimation of Groundwater Recharge Using GIS Method: A Case Study of Makotopong Village—Polokwane, South Africa

South Africa is a relatively dry country, with most rural areas experiencing high demand for water supply. Groundwater is one of the best alternative sources that can be used to augment the demand. However, this cannot sustainably be achieved unless accurate prediction of recharge to the groundwater aquifer is done. The objective of the study was to accurately estimate the groundwater recharge using ArcGIS method with a view of ensuring adequate groundwater for water supply exploitation. The study was conducted in Makotopong village in Polokwane. Data used in the study were sourced from diverse governmental agencies. Borehole logs were obtained from National Groundwater Archives. Geological and hydrogeological data were obtained from Council for Geoscience. All captured data were analysed to show the rainfall variations and estimation of groundwater recharge in different years. Groundwater recharge was estimated using ArcGIS 10.5. The simulated annual groundwater recharge varied from 0 mm to 51 mm with a mean recharge value of 12.04 mm/yr. The estimation of groundwater recharge using GIS methods resulted in a mean recharge value of 12.04 mm/year which shows a close comparison with previous studies conducted using Chlorine Mass Balance (CMB) and Water-Table Fluctuation (WTF). This implies that GIS is a potential tool that can be used to estimate groundwater recharge. It is recommended that GIS Method of estimating recharge be used in designing optimal sustainable groundwater supply systems.

Pore water isotope fingerprints to understand the spatiotemporal groundwater recharge variability in ungauged watersheds

AbstractReliable groundwater recharge quantification at the regional scale (e.g., watershed or subwatershed) is fundamental to sustainable water resource management. Although modeling at the watershed scale is gaining wide support, the long‐term monitoring needed for model calibration is often not readily available, as many watersheds worldwide remain ungauged. In response to this situation, we propose a new approach to estimate groundwater recharge at the watershed scale. This approach is fast and accurate and takes into account the existing variability without requiring long‐term monitoring. Only a single field campaign to acquire soil water content and pore water isotopic composition depth profiles is needed. The principle is to extend a physically based, one‐dimensional unsaturated zone flow model from the local (i.e., profile) to the watershed scale, using an index method for distributed recharge based on a GIS. The methodology was validated in a gauged watershed, where previous studies have estimated recharge using a spatialized water balance model calibrated using long‐term discharge monitoring data. Scaling was investigated by comparing recharge values obtained using the local‐scale approach at 10 study sites within the watershed with coinciding values obtained at the watershed scale. Recharge values were similar in terms of both dynamics and quantity. Using the pore water isotopic fingerprint of ungauged watersheds is therefore confirmed to be a suitable approach for understanding spatiotemporal recharge variability.

Spatial and temporal recharge estimation of the basement complex in Nigeria, West Africa

Study regionOsun Drainage Basin, Nigeria. Study focusEstimating spatial and temporal patterns of recharge is important for sustainable groundwater resources management. This is especially true for data poor regions, such as the Basement Complex in Nigeria, which has shallow aquifers, a proliferation of wells and no efficient groundwater monitoring network. This study evaluates the performance of a spatially distributed monthly water balance model (WetSpass-M) in estimating groundwater recharge. The WetSpass-M model has moderate data demands, which allows for comprehensive assessment of recharge. New hydrological insights for the region27 % of the rainfall in Osun drainage basin becomes recharge, while the remaining is lost through evapotranspiration (43 %), surface runoff (21 %) and interception (9 %). September is the month with highest recharge, ranging between 0 and 73 mm in the north and 129 up to 213 mm in the south and northeast of the basin. The study revealed the significance of the applied water balance model in understanding the spatial and temporal status of recharge. Therefore, the spatial and temporal patterns of recharge should be taken into consideration in preparing a sustainable groundwater resources management plan for the Osun drainage basin. Artificial recharge might be adopted to store storm water runoff during wet periods to improve the groundwater supply in dry months. Also, monthly groundwater withdrawals should be regulated in relation to spatial and temporal recharge patterns.

Estimating groundwater recharge for a freshwater lens in an arid region: Formative and stability assessment

AbstractThe formation of subsurface freshwater lenses on top of brackish groundwater is a fascinating hydrologic phenomenon that creates groundwater supplies of great potential value in arid regions. Information on the recharge quantity and mechanism of these lenses is both scarce and uncertain. This study examines the formation and macroscale stability of the Rawdatain freshwater lens in Kuwait, for which significant pre‐development data are available. The Rawdatain is a large (150 million m3) subsurface freshwater lens overlying brackish groundwater compared to the other freshwater lenses in the Arabian Peninsula. In this study, a three‐dimensional (3D) density‐dependent groundwater flow model is tested against the following data targets to estimate long‐term diffuse and focused groundwater recharge: (i) groundwater head, (ii) total dissolved solids (TDS) groundwater concentration, (iii) volume and vertical thickness of stored groundwater of three different water quality TDS ranges (0–700, 700–1000 and 1000–2000 mg/L) and (iv) geometrical shape features of the lens along cross‐sections. To better represent the spatial variation in TDS, six different recharge zones were assigned to allocate diffuse and focused recharge conditions. Twelve recharge rate scenarios, encompassing a wide range of feasible long‐term average annual recharge values (200,000–5,000,000 m3/year), were tested against the multiple targets and compared with the groundwater age of the Rawdatain lens. Based on comparison with data targets, the long‐term average annual recharge is estimated to be 500,000 m3/year. Scenarios of reduced recharge, which may occur due to changes in land‐use or climate, demonstrate the extremely slow response of the lens, which is in agreement with the slow development and formation of the lens (>2,000 years). Within a 100‐year time frame, a 50% reduction in annual recharge reduces the lens volumes by 21, 17 and 9% for the three water quality categories, respectively. This study demonstrates the stability of freshwater lenses in arid regions and also provides methodology for similar focused rainfall recharge freshwater lenses.

Groundwater recharge estimation using chloride mass balance: a case study of Nsukka local government area of Enugu State, Southeastern, Nigeria

Due to the unplanned growth of urbanization, industrialization and ever-growing population in Nsukka local government of Enugu State, the groundwater exploitations have increased dramatically. For proper planning and management of groundwater resources, there is need for a reliable estimate of groundwater recharge of the area. In the present study, for the first time, the chloride mass-balance method is adopted to estimate groundwater recharge in the study area. Measurements of chloride in groundwater and rainfall were made during 8-month period of the raining season beginning with the first rain on 5th March 2016 and the last rain on 10th October 2016. The main source of recharge considered was estimated from rainfall. The results are presented in the form of a map showing the spatial distribution recharge rate of the study area, which ranges from 1308.9 to 1683.3 mm/year and the recharge percentage of the total rainfall varies from 81.5 to 95.8%. The study area is characterized by moderate groundwater recharge due to the presence of high permeable underlying lithologies which associated with high porosity. Errors in the estimated recharge rate in work maybe large because of the limited data used in this analysis.

ESTIMATION OF GROUNDWATER RECHARGE ORIGINATING FROM AGRICULTURAL IRRIGATION AND RAINFALL IN SHYRAMYN PLAIN, IRAN

AbstractGroundwater recharge from rainfall and return flow of irrigation are essential for sustainable water resources management. There are many ways to estimate groundwater recharge. Most of them require a lot of field data, which limits their application in practice. To overcome this limitation, the rainfall infiltration breakthrough (RIB) model has been applied, which has the potential for estimating recharge using only rainfall, pumping rate, specific yield and groundwater level data in a semi‐arid region, the Shyramyn area, Iran. The groundwater recharge from rainfall (r) and the return flow of irrigation (λ) were estimated using the RIB model. Results of this effort indicated that the value of r varied around a ratio of 24.6% across the site, with a minimum and maximum of 1.1 and 27.0%, respectively, while λ varied with a minimum and maximum value of 0.0 and 33.0%, respectively.For the estimation of groundwater recharge most emphasis was usually put on recharge from rainfall. However, the findings of this study indicate that recharge from the return flow of irrigation played a major role in groundwater recharge and was 66.3% more than the recharge from rainfall. We hypothesize that this is a common process in similar areas where surface irrigation is applied. © 2019 John Wiley & Sons, Ltd.

Prediction of the response of groundwater recharge to climate changes in Heihe River basin, China

Accurate estimation of groundwater recharge is critical for evaluating the available freshwater resources in the Heihe River basin. Based on the statistical downscaling method coupled with the soil and water assessment tool, this study predicted the variations in precipitation, surface runoff, lateral flow, evapotranspiration, and groundwater recharge in the Heihe River basin under the A1B scenarios in the future 45 years (2019–2063). It was found that relative errors (Re), coefficient of determination (R2), and coefficient of Nash–Sutcliffe efficiency (Ens) at calibration and validation period were 19%, 0.90, 0.82 and 12%, 0.83, 0.75, respectively. These results indicated that the new SWAT models can be properly applied for predictions in the Heihe River basin. The next 45 years were divided into four stages, and precipitation change will follow the order stage III > stage I > stage IV > stage II. In addition, temperatures will gradually increase with time. Precipitation and evapotranspiration will be the major input and output of water resources, respectively. The surface runoff value with large precipitation stage will be nearly six times that of lateral flow. The daily highest temperature affects evapotranspiration, and the temporal variation rate of evapotranspiration is low because of extensive distribution of forests and grasslands. The groundwater recharge will reach a maximum in 2037–2046, which will be nearly two times that in 2019–2029. Groundwater recharge will be small in both 2047–2063 and 2030–2036. Precipitation is a major influence factor on groundwater recharge, but temperature slightly affects groundwater recharge. Underlying surface conditions such as land use, soil type, and properties also affect groundwater recharge. The precipitation after 2047 will not be very large, and temperatures will be high, and large evapotranspiration will lead to a rapid decrease in groundwater recharge.