Decrease In Groundwater Recharge Research Articles

Comparative assessment of recycled concrete and recycled asphalt aggregate in pervious concrete: emphasis on strength and life cycle assessment

ABSTRACT Pavements create an impermeable layer, contributing to a decrease in groundwater recharge and a rise in flood frequency in urban areas. Pervious concrete pavement (PCP) is considered one of the solutions to address the problems associated with impermeability. Due to the low-strength applications of PCP and to address the environmental issues associated with recycled concrete aggregate (RCA) and recycled asphalt pavement (RAP), studies have used them as replacements for natural aggregate (NA). Past studies recommended the optimum RCA or RAP content based on mechanical and durability investigations. This study investigates strength and environmental aspects of using RCA and RAP in PC by replacing NA with RCA and RAP at 30, 60, and 90% by volume. The compressive strength of RCA-PC mixtures at 7 days was found to be higher than that of RAP-PC mixtures, while RAP-PC mixtures displayed better abrasion resistance. Total embodied energy (TEE) and greenhouse gas emissions (GHG) with 90% replacement of RCA and RAP were 6.5–7.5% and 12.5–13.42% lower than control mixtures for different transportation distances, respectively. The cost-per-strength ratio indicated that RCA-PC mixtures were more preferred than RAP-PC mixtures. Overall, the study recommends 30% RCA/RAP content in PC, considering strength, cost, and environmental aspects.

The Effects of Wetland Degradation on Ecological Species

Wetlands are vital ecosystems that provide numerous ecological services, including flood control, water filtration, carbon sequestration, and habitat for diverse flora and fauna. However, human activities such as urbanization, agriculture, and infrastructure development have led to widespread wetland degradation worldwide. Wetland ecosystems diminished by 21-35% between 1700 and 2020 as a result of human interference, with at least 1.3 million square miles of wetlands lost globally—an area about the size of Alaska, Texas, California, Montana, New Mexico, and Arizona combined. This research used a documented methodology for extracting information from different books, conversations, conferences, and international organizations to understand the effects of wetland degradation on the decline of species and strategies for wetland conservation and restoration. This paper aims to elucidate the multifaceted effects of wetland degradation on ecological species. The results indicate that wetland degradation declines water quality, leading to alterations in water flow patterns, decreased groundwater recharge, and increased flooding downstream. This can result in the loss of biodiversity, as many species depend on specific water levels and habitats within wetlands. Moreover, the loss of wetlands diminishes their volume to store carbon, contributing to greenhouse gas emissions and exacerbating climate change. Furthermore, wetland degradation compromises water quality by reducing the natural filtration and purification functions of wetlands. Contaminants from agricultural runoff, industrial discharge, and urban pollution accumulate in degraded wetlands, posing risks to human health and aquatic ecosystems. Additionally, the loss of wetlands exacerbates erosion and sedimentation, leading to habitat destruction and loss of coastal resilience against storms and sealevel rise. Addressing wetland degradation requires a multifaceted approach, including policy interventions, restoration efforts, and public awareness campaigns. Effective wetland conservation strategies involve the preservation of existing wetlands, restoration of degraded ones, and sustainable management practices to mitigate further degradation. Collaborative efforts between governments, NGOs, local communities, and stakeholders are essential to safeguarding these critical ecosystems and the invaluable services they provide to the environment and society.

Distribution of tritium-helium groundwater ages in a large Cenozoic sedimentary basin (North German Plain)

The travel time of groundwater plays a major role in the understanding of hydrogeological systems; however, large data sets necessary for regional studies of groundwater age are rare. In this study, a unique large data set of groundwater samples analysed for tritium and helium isotopes collected over the last 20 years from Cenozoic aquifers of the North German Plain is explored. Hereby, the variety of natural and technical influences on the tritium-helium age, including screen depth and length, groundwater recharge rate and climatic effects, are investigated. To a sampling depth of ~40 m below ground level, the median tritium-helium age increases almost linearly with depth, reaching a maximum of 40 years. Below, the portion of older, tritium-free water rises. The tritium-helium ages of the tritium-bearing portion increase only slightly to a maximum of about 46 years. The depth distribution of the tritium-helium age shows a dependency on groundwater recharge rates. Considering the same depth level, younger ages are related to higher groundwater recharge rates as compared to groundwater that infiltrated in areas with lower recharge rates. This is especially observed for shallow depths. Tritium-helium ages younger than 40 years are reflected well in the atmospheric tritium input curves, while deviations from it can be related to anthropogenic influences such as input from nuclear power plants and irrigation with deep, tritium-poor groundwater. The regional distribution for shallow wells indicates increasing tritium-helium ages from west to east, corresponding to decreasing groundwater recharge rates due to the more continental climate in the east.

Water infiltration rate in the Kathmandu Valley of Nepal amidst present urbanization and land-use change

Abstract The rapid urbanization and land-use change prominently decreased groundwater recharge areas. Infiltration occurring through permeable areas is responsible for groundwater recharge. However, detailed studies of infiltration in low-income countries especially in human-encroached recharge areas are limited. Thus, this study mainly aims to measure the infiltration rate in the major recharge areas of the Kathmandu Valley (KV) using a double-ring infiltrometer (concentric ring size 30 and 15 cm). It also aims to estimate the volume of groundwater recharge with respect to the decrease in permeable areas in the northern part of the KV. The results revealed the infiltration rate ranging from 0.01 to 37.2 cm/h with an average of 7.3 ± 8.4 cm/h. The infiltration is found to be dependent upon land-use among different categories and organic matter among different soil properties. Additionally, the volume of water recharge in 2010, 2020, and 2030 was estimated as 67.73, 59.05, and 51.5 million cubic meters per year (MCM/year), respectively, which clearly showed a decrease in water recharge with respect to a decrease in the permeable areas. Hence, the findings would be useful for policymakers, stakeholders, and urban planners regarding the preservation and conservation of permeable areas for sustainable water resource management and urban flood management.

Quantitative partitioning of temporal origin of transpiration into pre- and post-plantation under deep-rooted vegetation on the Loess Plateau of China

Deep-rooted vegetation transpires a considerable amount of deep soil water with different ages in the unsaturated zone. However, the tradeoffs between new water of transpiration (temporally originating from post-planting precipitation) and old water of transpiration (temporally originating from pre-planting precipitation) across the vegetation lifespan are poorly understood. In this study, we collected soil samples from beyond 28 m soil depth on the Loess Plateau of China to investigate the influence of deep-rooted vegetation on the age of soil water and analyze the proportion of new and old water of transpiration in the unsaturated zone under grassland, 22-year-old apple orchard, and 17-year-old peach orchard. Water isotopes (2H, 18O, and 3H), solutes (chloride, nitrate, sulfate), and soil water content were used to identify the critical water ages in the unsaturated zone (one-year water age, water age corresponding to stand age, and the maximum water age of transpiration), and to determine soil water deficit, soil evaporation loss fraction, and potential groundwater recharge. The results showed that soil water mainly moved as piston flow in these soil profiles, and deep soil water largely came from heavy precipitation. Deep-rooted vegetation restrained new pore water velocity and potential groundwater recharge. New pore water velocity declined from 0.40 m yr−1 to 0.14 m yr−1 and 0.34 m yr−1 for apple and peach, respectively. Deep-rooted vegetation decreased groundwater recharge by 9.46 % for apple and 7.04 % for peach, compared to grassland. Over the vegetation lifespan, annual average transpiration was 500.56 mm yr−1 and 468.89 mm yr−1 with maximum water age of 63 years and 45 years for apple and peach, respectively. The transpiration of deep-rooted vegetation mainly used new water—94.97 % for apple and 97.47 % for peach. The total old water of transpiration was 553 mm for apple and 209 mm for peach. Our results identify the temporal sources of vegetation water use, offering new insights into the transpiration process of deep-rooted vegetation.

An Object- and Shapelet-Based Method for Mapping Planted Forest Dynamics from Landsat Time Series

Large-scale afforestation in arid and semi-arid areas with fragile ecosystems for the purpose of restoring degradation and mitigating climate change has raised issues of decreased groundwater recharge and ambiguous climatic benefits. An accurate planted forest mapping method is necessary to explore the impacts of afforestation expansion on fragile ecosystems. However, distinguishing planted forests from natural forests using remote sensing technology is not a trivial task due to their strong spectral similarities, even when assisted by phenological variables. In this study, we developed an object- and shapelet-based (OASB) method for mapping the planted forests of the Ningxia Hui Autonomous Region (NHAR), China in 2020 and for tracing the planting years between 1991 and 2020. The novel method consists of two components: (1) a simple non-iterative clustering to yield homogenous objects for building an improved time series; (2) a shapelet-based classification to distinguish the planted forests from the natural forests and to estimate the planting year, by detecting the temporal characteristics representing the planting activities. The created map accurately depicted the planted forests of the NHAR in 2020, with an overall accuracy of 87.3% (Kappa = 0.82). The area of the planted forest was counted as 0.56 million ha, accounting for 67% of the total forest area. Additionally, the planting year calendar (RMSE = 2.46 years) illustrated that the establishment of the planted forests matched the implemented ecological restoration initiatives over the past decades. Overall, the OASB has great potential for mapping the planted forests in the NHAR or other arid and semi-arid regions, and the map products derived from this method are conducive to evaluating forestry eco-engineering projects and facilitating the sustainable development of forest ecosystems.

Upwelling mechanisms of deep saline waters via Quaternary erosion windows considering varying hydrogeological boundary conditions

Abstract. Intrusion of deep saline waters into freshwater aquifers does not only endanger the regional drinking water supply, but also rivers and stagnant waters and their fauna are threatened by salinisation. The upwelling of highly mineralised saline waters in large parts of the North German Basin is favoured by the presence of Elsterian glacial erosion windows in the Lower Oligocene Rupelian Clay, the most important hydraulic confining unit in this region. Lower precipitation rates and decreasing groundwater levels as a consequence of global climate change, but also anthropogenic interventions, such as increasing extraction rates or the use of the deep geologic subsurface as a reservoir, decrease the pressure potential in the freshwater column and may possibly accelerate this primarily geogenic salinisation process in the coming years. Density-driven flow and transport modelling was performed in the scope of the present study to investigate the upwelling mechanisms of deep saline waters across Quaternary window sediments in the Rupelian. Simulation results show that the interactions between the groundwater recharge rate and anthropogenic interventions such as extraction rates of drinking water wells or the utilisation of the deep subsurface, have a significant influence on the groundwater pressure potential in the freshwater aquifer and associated saltwater upwelling. In all scenarios, salinisation is most severe in the sediments of the erosion windows. Hydraulically conductive faults also intensify salinisation if located nearside erosion windows or induce a more distributed or localised salinisation in aquifers with drinking water relevance in areas that do not intersect with erosion windows. A decline in groundwater recharge thereby significantly favours upward saltwater migration. The simulation scenarios further show that a decrease in groundwater recharge also results in freshwater salinisation occurring up to 10 years earlier, which underlines the need for waterworks to initiate effective countermeasures quickly and in time.

Effects of land use on thermal enrichment of urban stormwater and potential mitigation of runoff temperature by watershed-scale stormwater control measures

Stream temperature is critical to the survival and reproduction of fauna in cold-water ecosystems. Urbanization causes abrupt increases in ambient stream temperature via stormwater inputs while concurrently decreasing groundwater recharge and stream baseflow. Relatively little is known about how various urban land uses affect thermal load discharged to streams or whether a network of green infrastructure retrofitted at the watershed scale can ameliorate these impacts. Runoff temperature and hydrology were monitored at 17 urban and two forested watershed outlets to assess 1) how urban land use affects stormwater thermal pollution and 2) if thermal pollution can be mitigated through infiltrating stormwater control measures (SCMs). Significantly and substantially larger runoff temperatures (i.e., event mean temperature, event maximum temperature) and thermal loads were observed from every urban land use (without SCMs) in comparison to forested (i.e., surrogate for pre-development) conditions. Event mean temperatures generally followed the land use trend of parking lot > light industrial > commercial > heavy industrial > multi-family residential, single family residential > low density residential > forest. Retrofitted bioretention cells and permeable pavements were not successful in mitigating runoff temperature in residential watersheds compared to (1) watersheds without SCMs or (2) restoring temperature to surrogate pre-development conditions. SCMs were seldomly able to mitigate enough runoff volume to have a significant thermal load reduction compared to watersheds without SCMs. These results suggest stormwater management and cold-water species management have not yet been successfully integrated. More work is needed to optimize green infrastructure SCMs design for sufficient treatment of runoff to protect cold-water ecosystems from urban development. Beyond SCM implementation, wholistic watershed management practices (e.g., riparian buffers, clustered imperviousness, underground storage/conveyance) are needed to stem thermal enrichment of streams and lakes by stormwater.

Impacts of combined and separate land cover and climate changes on hydrologic responses of Dhidhessa River basin, Ethiopia

ABSTRACT The combined effects of climate and land cover changes influence hydrologic responses of a basin in an offsetting or synergistic manner depending on the nature and severity of the changes. As such, estimating the impacts of these environmental changes on hydrologic responses is crucial for planning water resources management. However, such a comprehensive study is missing in most basins of Ethiopia, particularly in the Dhidhessa River basin (DRB). The aim of this study is, therefore, to quantify the combined and separate impacts of land cover and climate changes on multiple hydrologic variables for the DRB. The Calibrated Soil and Water Analysis Tool (SWAT) model and statistical techniques were integrated for this study. Quantifying the separate and combined effects of land cover and climate changes on multiple hydrologic responses at a local scale, and determining the relative contribution of the changes are the strength of this study. The result indicated better performance of the SWAT model in simulating water balance components for the DRB. Significant changes in hydrologic responses were observed in response to the land cover changes, and the increasing trends of temperature and rainfall observed during the last 30 years in DRB. The result showed increasing actual evapotranspiration (AET), streamflow, and surface runoff while decreasing groundwater recharge. Surface runoff was more affected by land cover change than by climate change, whereas streamflow and AET were more affected by climate change than land cover change during the last 30 years in the basin. The combined effects of land cover and climate changes played an offsetting effect on groundwater recharge and AET. Overall, the simulated hydrologic responses will have negative effects on water resource availability and agricultural production in the basin and the surroundings. Therefore, implementing integrated watershed management strategies, such as soil and water conservation and afforestation, could minimize the negative impact.

ASSESSING THE HYDROLOGIC EFFECTS OF URBANIZATION THROUGH NUMERICAL MODELING USING SWAT: A CASE STUDY OF LAGUNA DE BAY BASIN

Abstract. Laguna de Bay, having a surface area of about 900 km2 is the largest freshwater lake in the Philippines, and is the most important water body in Metro Manila with its variety of uses ranging from aquaculture, irrigation, water supply and flood control. Due to its available resources and strategic location, over extraction, land conversion, and urbanization, have resulted in massive changes in the lake's watershed. The objective of this study is to simulate the impact of land cover change, particularly urbanization, on the hydrology of Laguna de Bay watershed. By hypothetically converting brushland to urban areas and using ArcSWAT to simulate the effects of urbanization, discharges and water balances were assessed. The long-term hydrologic simulations showed an annual increase of 20.6 m3/s (68%) in surface runoff and a 12.8 m3/s (26%) decrease in groundwater recharge for the entire watershed as urban areas increase. The mean seasonal flows were 75. m3/s during the dry season and 149.4 m3/s during the wet season for the original land cover, and 70.2 m3/s and 154.1 m3/s for the urbanized land cover, during the dry and wet seasons, respectively. Water percolating into the aquifers beneath the ground were also lessened by 13.6 m3/s (23%). The calibration of Marikina subbasin resulted to a satisfactory percent bias (PBIAS), Nash-Sutcliffe (NSE), and the ratio of the root-mean-square error to the standard deviation of measured data (RSR). Other subbasins resulted in a relatively lower performance rating due to limited available monitoring stations within the basin.

The Impact of Predicted Climate Change on Groundwater Resources in a Mediterranean Archipelago: A Modelling Study of the Maltese Islands

The effects of changes in climate predicted for 2100—reduction in recharge, increase in water demand and sea-level rise—on groundwater volume and saltwater intrusion have been quantified in the Maltese Islands, an archipelago located at the center of the Mediterranean Sea. A three-dimensional density dependent and heterogeneous model, working in transient conditions, was developed based on morphological and geological information. The hydraulic conductivity and porosity of the lithological formations were derived from previous tests and studies conducted on the islands. The complex fault system intersecting the area has also been included in the model. The results show that among the three considered factors affecting groundwater resources, the most significant is the increase in water demand, which is closely followed by the decrease in groundwater recharge. Sea-level rise plays a marginal role. The 80-year simulation period showed that these combined impacts would cause a loss of more than 16% of groundwater volume.

Groundwater-fed oasis in arid Northwest China: Insights into hydrological and hydrochemical processes

As an inland groundwater-fed oasis in northwest China, the Dunhuang West Lake Wetland (DWLW) has been threatened by decreasing groundwater recharge over the past several decades. Understanding recharging processes for DWLW is a key step for better protection of the oasis, but poorly studied. To this end, we carried out a comprehensive water chemistry and isotope sampling and analysis, by taking the oasis and its water sources as a complete system to reveal the oasis water recharging mechanism and flow paths. Water samples, including mountain snowmelt water, river water, groundwater, spring and lake water, were collected within and around the DWLW, and their environmental isotopes (δ18O and δD) and water chemistry were analysed. Results showed that the stable isotope values exhibited strong spatial variations, ranging from −90.69‰ to −42.45‰ for δD and from −13.81‰ to −2.90‰ for δ18O. The isotope values were extremely depleted for snowmelt water, followed by river water, groundwater, spring water, and were most enriched in lake water. The difference in isotopic values from the different water bodies indicates that seasonal rivers primarily originate from the snowmelt water in the adjacent mountains, discharge into the aquifer through infiltration, then groundwater rises up by forms of springs to the lake oases, the river and groundwater interacted frequently, causing significant changes in solute in different positions. The ion concentrations accumulated continuously along the flow path, the total dissolved solid content varied from 416 mg/L in river water to 20360 mg/L in lake water, and the dominant anion facies changed systematically from HCO3- to SO42- then Cl-. The ionic ration plot, chlor-alkali index and saturation index demonstrated that dissolution of minerals plays a major role in the change in chemical composition, and other processes such as carbonate precipitation associated with cation exchange reaction also influence the chemical composition. Our results are helpful for understanding the hydrological and hydrochemical processes in arid groundwater-fed oases, and can be also useful for rational management and assessment of regional-scale groundwater resources in oases.

Investigating the Effects of Agricultural Water Management in a Mediterranean Coastal Aquifer under Current and Projected Climate Conditions

Coastal delta plains are areas with high agricultural potential for the Mediterranean region because of their high soil fertility, but they also constitute fragile systems in terms of water resources management because of the interaction of underlying aquifers with the sea. Such a case is the Pinios River delta plain located in central Greece, which also constitutes a significant ecosystem. Soil and Water Assessment Tool (SWAT) and SEAWAT models were combined in order to simulate the impact of current water resources management practices in main groundwater budget components and groundwater salinization of the shallow aquifer developed in the area. Moreover, potential climate change impact was investigated using climate data from Regional Climate Model for two projected periods (2021–2050 and 2071–2100) and two sea level rise scenarios (increase by 0.5 and 1 m). Modeling results are providing significant insight: although the contribution of the river to groundwater inflows is significant, direct groundwater recharge from precipitation was found to be higher, while capillary rise constitutes a major part of groundwater outflows from the aquifer. Moreover, during the simulation period, groundwater flow from the aquifer to the sea were found to be higher than the inflows of seawater to the aquifer. Regarding climate change impact assessment, the results indicate that the variability in groundwater recharge posed by the high variability of precipitation during the projected periods is increasing the aquifer’s deterioration potential of both its quantity and quality status, the latter expressed by the increased groundwater Cl− concentration. This evidence becomes more significant because of the limited groundwater storage capacity of the aquifer. Concerning sea level rise, it was found to be less significant in terms of groundwater salinization impact compared to the decrease in groundwater recharge and increase in crop water needs.

Modeling hydrological response to land use/cover change: case study of Chirah Watershed (Soan River), Pakistan

Assessment of land use change impacts on watershed hydrologic processes is of great importance to draw the attention of water resource managers and policy makers for better planning and management of the shrinking resources for the survival of surrounding population of the region. Chirah watershed is an important hydrologic unit which generates an average of 0.53 MCM water per day. Soan River originates from here, supplying an average inflow of 0.2 MCM day−1 to Simly Dam. Since a couple of decades, rainfall variability coupled with growing population is threatening Soan River flows. Deforestation and land use/land cover (LULC) changes have affected the natural pathways of water, decreased groundwater recharge, and triggered flash floods. Therefore, the aim of this research was to assess the impact of LULC changes on the hydrologic processes of the watershed using the Soil and Water Assessment Tool (SWAT), a hydrological model to propose management strategies. LULC change assessment was carried out on Landsat-5 TM and OLI_TIRS images through ‘Supervised Classification’ at four-time steps (1990, 1999, 2010, and 2016). Due to limited ground observations, corresponding Google Earth images were used in mapping. The SWAT model was evaluated using the Nash-Sutcliffe efficiency (NSE) and relative volumetric error (RVE) objective functions on monthly time steps. The NSE achieved during calibration and validation, 0.63 and 0.45, respectively, indicates acceptable levels of model performance despite outliers in the hydro-meteorological dataset. Similarly, the RVE was less than ±5% during both periods, indicating that the model simulated water balance reasonably well. Changes in LULC resulted in alteration of all the hydrological parameters. Conversion of scrub thorny forest (14.74%) into built-up areas (9%) resulted in higher imperviousness which triggered runoff to 24% and lowered groundwater recharge by 8% in 27 years indicating that the hydrologic regime is sensitive to LULC changes.

The Impacts of Water Cycle Components on Streamflow in a Changing Climate of Korea: Historical and Future Trends

This paper investigates the historical and future trends in water balance components and their impacts on streamflow. The trend analyses were applied to the daily climatic and hydrologic variables from 109 subbasins in Korea during the historical period and future period obtained by a multimodel ensemble of 13 global circulation models (GCMs) of the Coupled Model Intercomparison Project, Phase 5 (CMIP5). A calibrated hydrologic model, the precipitation-streamflow modeling system (PRMS) model, was applied to obtain hydrologic data. The results revealed apparent trends in streamflow, with increases in spring and decreases in the other seasons during the historical period. The reduction (or increase) in the amount of streamflow was counterbalanced by the reduction (or increase) in precipitation, groundwater, and soil moisture, which was mainly impacted by the increase (or reduction) in actual evapotranspiration. However, opposite trends are projected for the future period for streamflow and water cycle components, in which spring and winter are projected to have increasing trends mostly counterbalanced by the decreasing trends in precipitation and groundwater. The reasons for the reduction in streamflow include elevated evapotranspiration compared to precipitation, reduced soil moisture, and a significant decrease in groundwater recharge. In addition, the results of the seasonal variability among basins revealed higher variability in summer for the historical period and in winter for the future period, with maximum variability in the Sumjin River basin, indicating that streamflow fluctuated more strongly in the Sumjin River basin during the historical and future periods.

Modelling study to quantify the impact of future climate and land use changes on water resources availability at catchment scale

Abstract The focus of this study was to investigate the impact of climate and land-use changes on water resources and to find suitable drought indices to identify the occurrence, frequency and severity of the past and future drought events. The Ebbw catchment, Wales, UK was selected for this study. Data for the 1961–2012 period were used as input to the DiCaSM model. Following model calibration and validation, the model was run with UKCP09 future climate scenarios for three periods (30 years each) up to 2099 under three emission scenarios. The reconnaissance drought index, the standardized precipitation index, soil moisture deficit and the wetness index were able to reproduce the past drought events. The data of UKCP09, simple change factors to temperature (± °C) and rainfall (%) using Joint Probability plot and daily values of the weather generator were input to the model. The projections indicated that the streamflow and groundwater recharge are likely to increase in winter and to decrease in spring, summer and autumn. Under all emission scenarios, the greatest decrease in groundwater recharge and the streamflow is projected in the 2050s and 2080s under high emission scenario. Moreover, under medium and high emission scenarios, severity and frequency of the drought events are likely to be high. Land use change from grass and/or arable to woodland had significant impact on water resources.

Numerical groundwater flow modeling of the Kombolcha catchment northern Ethiopia

Intensive groundwater extraction is a changing groundwater system. It is also the main challenge for future groundwater availability. In this study, numerical groundwater flow model was developed in Kombolcha catchment, Ethiopia by using MODFLOW-OWHM. To address this concern, the conceptual model was built by analyzing the hydrogeological data. The groundwater model was calibrated under the steady-state condition to produce the best match between the simulated and observed hydraulic head. The simulated outflow of the MODFLOW model was 358,221.09 m3/day which is nearly equal to 358,221.08 m3/day of groundwater inflow with a difference 0.01 m3/day and zero discrepancies. The subsurface inflow covers the most percentage (76%) in the budget and surface outflow contributes about 66% of the total groundwater outflow. The model result shows that the Kombolcha aquifer system is highly sensitive to change of hydraulic conductivity. Prediction of this aquifer behavior for increasing well withdrawal and decreasing recharge scenarios has been carried out. The effect of increasing withdrawal by 25, 50 and 100% results in a decline of groundwater level by 6.77, 12.15 and 24.37 m, respectively, whereas the effect of decreasing groundwater recharge by the same percentage of withdrawal results in a decline of groundwater level by 4.27, 6.34 and 11.25 m, respectively. This model can be as a tool to understand the aquifer system and sustainable utilization of groundwater resources.

Mapping groundwater resiliency under climate change scenarios: A case study of Kathmandu Valley, Nepal

Groundwater resources of Kathmandu Valley in Nepal are under immense pressure from multiple stresses, including climate change. Due to over-extraction, groundwater resources are depleting, leading to social, environmental and economic problems. Climate change might add additional pressure by altering groundwater recharge rates and availability of groundwater. Mapping groundwater resilience to climate change can aid in understanding the dynamics of groundwater systems, facilitating the development of strategies for sustainable groundwater management. Therefore, this study aims to analyse the impact of climate change on groundwater resources and mapping the groundwater resiliency of Kathmandu Valley under different climate change scenarios. The future climate projected using the climate data of RCM's namely ACCESS-CSIRO-CCAM, CNRM-CM5-CSIRO-CCAM and MPI-ESM-LR-CSIRO-CCAM for three future periods: near future (2010–2039), mid future (2040–2069) and far future (2070–2099) under RCP 4.5 and RCP 8.5 scenarios were bias corrected and fed into the Soil and Water Assessment Tool (SWAT), a hydrological model, to estimate future groundwater recharge. The results showed a decrease in groundwater recharge in future ranging from 3.3 to 50.7 mm/yr under RCP 4.5 and 19–102.1 mm/yr under RCP 8.5 scenario. The GMS-MODFLOW model was employed to estimate the future groundwater level of Kathmandu Valley. The model revealed that the groundwater level is expected to decrease in future. Based on the results, a groundwater resiliency map of Kathmandu Valley was developed. The results suggest that groundwater in the northern and southern area of the valley are highly resilient to climate change compared to the central area. The results will be very useful in the formulation and implementation of adaptation strategies to offset the negative impacts of climate change on the groundwater resources of Kathmandu Valley.

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.

Estimating groundwater recharge on the southern slope of Mount Kilimanjaro, Tanzania

This paper used three methods namely: water-table fluctuation (WTF), soil moisture balance (SMB), and chloride mass balance (CMB) to estimate groundwater recharge in a degraded Kahe catchment located on the southern slope of Mt. Kilimanjaro, Tanzania. Three methods yielded different groundwater recharge rates. Results of the WTF method showed that recharge in the catchment was about 248.4 million m3/year, whereas those of CMB and SMB methods were 156.0 and 132.1 million m3/year, respectively. The estimated recharge rates ranged between 132.1 and 248.4 million m3/year with an average of 191.34 ± 27.80 million m3/year. Differences in the estimated rates can be attributed to the scales of measurements, assumptions in each method, and the quality of the data used. Satellite images taken in between 2000 and 2017 were used to estimate the land-use changes and their impacts on groundwater recharge in the study catchment. Analyzed satellite images showed that over the 17-year period, natural forests and bushes and shrubs decreased by 3.6 and 4.1%, while agricultural land and built-up area increased by 12.8 and 0.8%, respectively. Using SMB method, we found that these land-use changes have contributed to a decrease in groundwater recharge of about 42% between 2000 and 2017 (i.e., from 227.8 to 132.1 million m3/year). The findings from this study are useful for assessing the potential impacts of land-use change on water resources in the catchment.