Machine learning-based approach coupled to SWAT model to dynamically quantify the natural groundwater recharge

Groundwater recharge concepts.- Groundwater recharge concepts.- An unexpected factor affecting recharge from ephemeral river flow in SWA/Namibia.- On the continuity of aquifer systems on the crystalline basement of Burkina Faso.- Groundwater recharge estimation (Part 1): physical/chemical methods.- A review of some of the physical, chemical and isotopic techniques available for estimating groundwater recharge.- Evaporation in arid and semi-arid regions.- Satellite remote sensing and energy balance modeling for water balance assessment in (semi-)arid regions.- A proposed study of recharge processes in fracture aquifers of semi-arid Botswana.- Estimation of natural groundwater recharge under Saudi Arabian arid climatic conditions.- Solute profile techniques for recharge estimation in semi-arid and arid terrain.- Recharge estimation from the depth-distribution of environmental chloride in the unsaturated zone - Western Australian examples.- Natural recharge measurements in the hard rock regions of semi-arid India using tritium injection - a review.- Comparison of recharge estimates from injected tritium technique and regional hydrological modelling in the case of a granitic basin in semi-arid India.- Studies on natural recharge to the groundwater by isotope techniques in arid Western Rajasthan, India.- Groundwater recharge estimation (Part 2): numerical modelling techniques.- Numerical and conceptual models for recharge estimation in arid and semi-arid zones.- Methods for estimation of natural groundwater recharge directly from precipitation - comparative studies in sandy till.- The principles of inverse modelling for estimation of recharge from hydraulic head.- Estimating natural recharge of ground water by moisture accounting and convolution.- Natural ground water recharge estimation methodologies in India.- BALSEQ - a model for the estimation of water balances, including aquifer recharges, requiring scarce hydrologic data.- Applications and case studies.- Quantification of groundwater recharge in arid regions: a practical view for resource development and management.- Groundwater recharge studies in semi-arid Botswana - a review.- Rainfall-runoff-recharge relationships in the basement rocks of Zimbabwe.- Recharge characteristics of aquifers of Jeddah-Makkah Taif region.- Groundwater recharge and subsurface flow in the Comodoro Rivadavia area, Chubut Province, Argentina. Isotopic and hydrochemical study.- Groundwater recharge over Western Saudi Arabia.- Natural recharge of karst aquifers in Western Taurus region (southwestern Turkey).- Estimation of recharge of sand aquifer of the Island of Mannar Sri Lanka.- Groundwater recharge from three cheap and independent methods in the small watersheds of the rainforest belt of Nigeria.- Quantitative estimation of ground-water recharge in dolomite.- Quantitative estimation of ground-water recharge in the Pretoria-Rietondale area.- Analysis of long-duration piezometric records from Burkina Faso used to determine aquifer recharge.- Humid zone recharge: a comparative analysis.- Humid and arid zone groundwater recharge - a comparative analysis.- List of participants.

Integrating physical models with socio-economic considerations is essential to sufficiently analyze complex hydrological systems and design effective strategies for groundwater management. This integrated approach offers an effective means of detecting links between aquifer properties and groundwater processes. This study aims to assess the impact of human activities and climate changes on groundwater resources. In particular, the final goal is to quantify the spatial distribution of natural groundwater recharge, which is needed to assess the impact of anthropogenic factors on sustainable groundwater management in the Chiba watershed, NE of Tunisia as an example of a stressed hydrosystem.The proposed methodology is based on the estimation of natural groundwater recharge through hydrological modeling with the use of the SWAT model while considering land use/land cover changes occurring within the study area, coupled with the DPSIR (Drivers-Pressures-States-Impacts-Responses) socio-economic approach for time period 1985-2021. The surveys were constructed and processed based on the probability of occurrence for the degree of satisfaction with arguments related to the DPSIR parameter within the category of the 5-point Likert scale (ranging from level 1 - very low to level 5 - very high), including mean, standard deviation, and the consensus (CnS).Chiba watershed was selected as a case study since its climate is representative of the Tunisian semi-arid context, and due to the high vulnerability of the existing groundwater systems with respect to human activities.The hydrological simulations suggest a gradual decrease of 33% in the aquifer's natural recharge over the entire time period. The long-term average value of the annual recharge rate per sub-basin does not exceed 3 mm/year, keeping groundwater recharge levels in the basin relatively low. This observation is mainly attributed to climate change with CnS of 0.6 and over-exploitation of the water sources for irrigation purposes (CnS = 0.62), leading to aquifer depletion and degradation of groundwater-dependent ecosystems (CnS = 0.73). These results suggest that different management practices, such as more conservative water use (CnS = 0.6), long-term monitoring and Managed Aquifer Recharge (MAR) with wastewater (CnS = 0.76), can help rural residents to diversify their economies while preserving these water resources. However, although attempts of MAR have been undertaken, they remain insufficient to counter the pressure on the coastal aquifer, underlining the importance of preserving the fragile semi-arid landscape.The proposed approach is applicable to other regions having similar climatic and socio-economic conditions. It also demonstrates that pure modeling solutions need to be coupled to the socio-economic approaches to be able to constitute a solid asset for sustainable water resources management of stressed hydro-systems. AcknowledgmentsThis work is funded by National Funding Agencies from Germany,  Cyprus, Portugal, Spain, and Tunisia under the Partnership for Research and Innovation in the Mediterranean Area (PRIMA) and supported under Horizon 2020 by the European Union’s Framework for Research and Innovation.

The sensitivity of future groundwater recharge and temperature development was investigated for three alluvial aquifers in the urban agglomeration of the city of Basel, Switzerland. For selected climate projections groundwater recharge and the associated temperature imprinting of aquifers, which are mainly determined by artificial groundwater recharge and infiltrating surface water, were investigated.3D numerical groundwater flow and heat-transport modeling, allowed quantifying and differentiating between natural and artificial groundwater recharge and thermal impacts. For aquifers where the infiltration of river water is an important component in the groundwater balance, the effects of climate change will be influenced by changes in river flow and thermal regimes and also by artificial groundwater recharge of surface water. Considering all climate scenarios investigated, the net heat input from river water infiltration for the Lange Erlen case study area increases by an average of 42 % by 2055 and 62 % by 2085 compared to the reference year 2000. Together with further heat inputs, particularly by artificial groundwater recharge, the temperatures of the extracted drinking water would increase by 0.4 to 1.3 K by 2055 and 0.7 to 3.1 K by 2085. In the Hardwald case study area, the most significant heat exchange occurs by artificial groundwater recharge. As a result, and considering all climate scenarios investigated, heat loss by groundwater extraction increases by an average of 38 % during the winter months from the year 2000 to the year 2085. The increased heat input, especially in the summer months, results in a temperature increase of the extracted drinking water of 0.2 to 1.0 K by 2055 and 0.6 to 4.0 K by 2085. In the Lower Birs Valley case study area, net heat input from river water infiltration increases by an average of 42 % by 2055 and 62 % by 2085. Correspondingly, the temperatures of the extracted drinking water increase by 0.9 to 3.2 K by 2055 and by 0.3 to 5.4 K by 2085.The quantitative assessment of climate change impacts on the groundwater resources presented allows to differentiate between hydraulic and thermal impacts of natural and artificial groundwater recharge processes. Accordingly, individual drinking water wells are exposed differently to the various components of groundwater recharge. Seasonal shifts in natural groundwater recharge processes and adaptation strategies related to artificial groundwater recharge could therefore be an important factor affecting groundwater resources in future. Moreover, increased groundwater recharge from artificial groundwater recharge systems in summer months and the interaction with surface waters during high runoff periods, which will occur more often in winter months, are likely to strongly influence groundwater recharge and temperatures.

A critical review of groundwater budget myth, safe yield and sustainability

This abstract summarizes the preliminary results from groundwater recharge estimates at Kolkata, West Bengal, which is under the Kolkata Metropolitan Corporation (KMC) covering an area of 187.33 sq.km. Water is indispensable to all life on earth. However, freshwater is constantly formed newly through a phenomenon known as hydrological cycle. Groundwater is the source of about 33% of the water that county and city water departments supply to households and businesses. Groundwater recharge is the process by which water percolates down the soil and reaches the water table, either by natural or artificial methods. Here, natural groundwater recharge is dealt with. Quantification of the rate of natural groundwater recharge is a pre-requisite for efficient groundwater resource management. For a region like Kolkata, there is large demand for groundwater supplies, where such resources are the keys to economic development. However, the rate of aquifer recharge is one of the most difficult factors to measure in the evaluation of groundwater resources. Estimation of recharge, by any method, is normally subject to large uncertainties and errors. In this study, various methods of estimating natural groundwater recharge in Kolkata region (2016) are outlined taking one year precipitation and evapotranspiration data, calculating the runoff of this region and getting the net storage capacity of soil, which is mostly alluvial. This study estimates the amount of recharge taking place in Kolkata and it critically reviewed with regard to their limitations and associated uncertainties leading to the need for artificial groundwater recharge by roof-top rainwater harvesting. And finally, a detailed design for a rooftop rain water harvesting system is provided.

Groundwater is the major source of drinking water in both urban and rural India. Estimation of natural groundwater recharge is essential for the sustainable development of groundwater. Natural recharge was estimated by various methods, such as the water level fluctuation method, water balance method, linear regression model, and nonlinear regression model. The recharge estimates by the water balance method was compared with the recharge obtained from the water level fluctuation method for the study area and found to be in good agreement. Estimation of recharge by the water level fluctuation method is laborious, and envisaging the difficulties in the availability and reliability of data, the water balance method is taken as the standard for developing regression equations in the present study. Simpler linear and nonlinear regression models were developed for the study area to estimate natural recharge by correlating with the water balance model. The models were calibrated with 10-yr data and validated with 5-yr data. The statistical analysis showed that no significant difference exists between the recharge estimate by the water balance method and the two estimates of natural recharges, such as linear regression and nonlinear regression models. The average recharge percentages from the water level fluctuation method, water balance method, linear regression model, and nonlinear regression model are 15.09%, 14.92%, 14.62%, and 14.57%, respectively, for the watershed during the study period. The study proves that regression equations can be efficiently used in recharge computation with proper calibration for ungauged basins, and laborious data-intensive computation methods can be eliminated.

The response of aquifers with contrasting climate and geology to climate and land cover change perturbations through natural groundwater recharge remains inadequately understood. In Tanzania and elsewhere in the world, studies have been conducted to assess the impact of climate change and variability, and land use/cover changes on stream flow using different models, but similar studies on groundwater dynamics are inadequate. This study, therefore, examined the influence of land use/cover and climate dynamics on natural groundwater recharge in basins with contrasting climate and geology in Tanzania, applying the modified soil moisture balance method, coupled with the curve number (CN). The method hinges on the balance between the incoming water from precipitation and the outflow of water by evapotranspiration. The different parameters in the soil moisture balance method were computed using the Thornthwaite Water Balance software. The potential evapotranspiration (PET) was calculated using the daily maximum and minimum temperatures, utilizing two-temperature-based PET methods, Penman–Monteith (PM) and Hargreaves–Samani (HS). The rainfall data were obtained from the gauging stations under the Tanzania Meteorological Agency and some additional data were acquired from climate observatories management by water basins. The results show that there has been a quasi-stable CN in the Singida semi-arid, fractured crystalline basement aquifer (74.2 in 1997, 73.64 in 2005, and 73.87 in 2018). In the Kimbiji, humid, Neogene sedimentary aquifer, the CN has been steadily increasing (66.69 in 1997, 69.08 in 2008, and 71.42 in 2016), indicating the rapid land cover changes in the Kimbiji aquifer as compared to the Singida aquifer. For the Kimbiji humid aquifer, the PET calculated using the Penman–Monteith (PM) method for the 1996/1997, 2007/2008, and 2015/2016 hydrological years were 1156.5, 1079.5, and 1143.9 mm/year, respectively, while for the Hargreaves–Samani (HS) method, the PET was found to be 1046.1, 1138.3, and 1204.4 mm/year for the 1996/1997, 2007/2008, and 2015/2016 hydrological years, respectively. For the Singida semi-arid aquifer, the PM PET method resulted in 2083.3, 2053.6, and 1875.4 mm/year for the 1996/1997, 2004/2005, and 2017/2018 hydrological years, respectively. The HS method produced relatively lower PET values for the semi-arid area (1839.4, 1814.7, and 1710.2 mm/year) for the 1996/1997, 2004/2005, and 2017/2018 hydrological years, respectively. It was equally revealed that the recharge and aridity indices correspond with the PET calculated using two temperature-dependent methods. The decline of certain land covers (forests) and increase in others (built-up areas) have contributed to the increase in surface runoff in each study area, possibly resulting in the decreasing trend of groundwater recharge. An overestimation of the PET using the HS method in the Kimbiji humid aquifer was observed, which was relatively smaller than the overestimation of the PET using the PM method in the Singida semi-arid aquifer. Despite the difference in climate and geology, the response of the two aquifers to rainfall is similar. The combined influence of climate and land cover changes on natural groundwater recharge was observed to be prominent in the Kimbiji aquifer, while only climate variability appreciably influences natural groundwater recharge in the Singida semi-arid aquifer. El Nino and the Southern Oscillation as part of the climate variability phenomenon dwarfed the time lags between rainfall and recharge in the two basins, regardless of their difference in climate and geology.

An entropy-based approach is developed for assessing natural groundwater recharge in unconfined aquifers from Southern India. The wells are located in weathered zones which exhibit spatial variability in natural recharge. To determine the fractional amount of rainfall (called natural recharge) marginal entropies and transinformation of rainfall and depth to the water table at selected wells are calculated. Then a ratio of transinformation to marginal entropy of rainfall is used as a measure for assessing natural recharge. Calculated natural recharge yields a good agreement with the results of recharge zones obtained using Remote Sensing (RS) and Geographical Information System (GIS) techniques.

Groundwater recharge means different things to different people. For example, to an agronomist, water which moves beneath the root zone of crops represents a loss in yield and so should be minimised. Those who are interested in water resources, take the opposite view. A few of the reasons for studying natural groundwater recharge are: to determine the safe yield of a groundwater system; to assess the extent of development of secondary salinisation following land clearing; and, for those interested in storage of waste materials, to identify areas of very low groundwater recharge. Only natural recharge, either local or localized will be considered here. Local (or diffuse) recharge is defined as that reaching the water table by percolation of precipitation in excess of evapotranspiration, through the unsaturated zone. Localized recharge occurs following runoff and subsequent ponded infiltration through low-lying areas, streams or lakes.

Water harvesting works had been conducted at Jamka micro-watershed of Saurashtra region of Gujarat in India for augmenting artificial groundwater recharge in hard rock aquifers of the semi arid region. In present study groundwater recharge of Jamka micro-watershed was estimated. The natural groundwater recharge through rainfall in the study area was estimated using empirical equations and the artificial groundwater recharge through water harvesting structures which was estimated using remote sensing and GIS. The area under submergence due to water harvesting structures is estimated using remote sensing images. The groundwater recharge in study area was also estimated using water table fluctuation method and compared with total recharge through rainfall and water harvesting structures. The natural groundwater recharge through rainfall in the study area was found varying from 11 to 16 per cent of annual rainfall. The total groundwater recharge in the study area was estimated 390.29 ha m, in which the contribution of recharge through water harvesting structures was about 38.53%; this revealed that the water harvesting structures played an important role in increasing the groundwater recharge in the region.

The El Khairat aquifer located at the eastern center of Tunisia is mainly recharged by infiltration of flood water through beds of ephemeral streams. Since late 70s, the aquifer showed a continuous water table decline due to an excessive increase of groundwater extraction. The situation worsened by the damming of the El Khairat wadi which is the most important wadi of the region. Artificial recharge campaigns were carried out by Tunisian water agency to re-establish the natural groundwater recharge of the aquifer. They consisted of releasing water from the dam reservoir to the natural downstream bed of the wadi channel. This paper aims to assess the efficiency of the artificial groundwater recharge operations by developing a conceptual rainfall-runoff model. The model input consists of the daily water volume released from the dam. The wadi bed is divided into several serial reaches. For each reach, the production function is represented by a soil store and four transfer reservoirs. The model calibration consists of reproducing the daily surface runoff volume measured at the runoff gauging stations and the water table level measured at the piezometers located in close proximity of the wadi course. The modelling results indicate an infiltration coefficient ranging from 40 to 80%. Despite this high infiltration rate, the mean annual recharge in artificialized regime remains below the natural recharge. The construction of El Khairat dam could be a good resource management alternative under certain constraints as increasing the recharge campaigns frequency and avoiding releases with high discharge rate.

Accurate knowledge of natural recharge is an essential input to devise an effective management plan for groundwater resources. The paper presents an approach of utilizing airborne electromagnetic (AEM) resistivity data coupled with precipitation using lithology constrained rainfall (LCR) recharge relationships to estimate natural recharge in a heterogeneous crystalline hard rock aquifer. AEM method, having the ability of rapid and dense data sampling, helps in improving the spatial estimation of groundwater recharge at a regional scale. A demonstrative study has been carried out in a granite hard rock terrain of southern India. The LCR recharge estimates are validated by the recharge estimates from the well‐defined water table fluctuation (WTF) method. The estimated water level using LCR recharge is found in good agreement with the measured water level in the field, which indicates the robustness of the methodology. The paper also presents the role of data density on its spatial relationship through variogram analysis.

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.

Water scarcity is one of the major critical affecting arid climate countries. In addition, population growth and climate change are threatening the sustainable development of water resources in the upcoming decades. Therefore, managing groundwater can solve water scarcity such that sustainable development is ensured for future generations. Hence, it is crucial to assess the current quantity of groundwater by analyzing groundwater variables. Thus, natural groundwater recharge could be utilized as an indicator to assess groundwater quantity conditions. This study aims to estimate natural groundwater recharge in an arid unconfined aquifer. El-Qaa plain in Sinai, Egypt was chosen as a case study. Recharge was estimated taking into consideration spatial and temporal variability. To accomplish this, the WetSpass (Water and Energy Transfer between Soil, Plants, and Atmosphere under quasi-Steady State) model was applied. The model was run using morphological, landuse – land cover and climate data from 1986 to 2015 with a monthly time step. To calibrate the model, the isotope signature of δ18O and δ2 H of water was analyzed to determine the natural groundwater recharge of the aquifer. The obtained recharge value was utilized as a reference value for the calibration process. The results were validated using a finite-difference groundwater flow model (MODFLOW). The recharge values were imported to MODFLOW followed via a transient run from 2000 to 2011. The validation was conducted by comparing the simulated groundwater level with the observed ones. After validation process, the inter-annual and seasonal variability of recharge were determined, and a relationship between recharge and other hydrological parameters was deduced. In addition, the recharge distribution was mapped to depict the recharge spatial variability. The results show that the current recharge rate ranges from approximately 8.10 to 16.62 mm/yr, with a mean annual recharge rate of nearly 12.36 mm/yr. The study might be useful for hydrogeologists for determining potential recharge in the study area, groundwater modelers for developing a reliable groundwater flow model, and decision-makers for planning appropriate future sustainable development through water resources management.

Estimation of Natural Recharge and Groundwater Build up in the Bandung Groundwater Basin Contributed from Rain Water Infiltration and Inter-aquifer Transfer