Increased Groundwater Recharge Research Articles

The Influence of Fresh Submarine Groundwater Discharge on Seawater Acidification Along the Northern Mediterranean Coast of Israel

AbstractIn the oligotrophic Southeastern Mediterranean Sea (SEMS), it has been shown that dissolved inorganic nutrient (DIN) from fresh submarine groundwater discharge (FSGD) enhance primary production in coastal waters. In this study pH, Total Alkalinity (TA) and DIN of seawater and fresh water in a sea‐cave in the northern part of the Israeli Mediterranean coast and a nearby contact spring, respectively, were measured during October 2018–March 2020. The results show gradients of measured salinity, TA, pH and DIN along the cave axis year‐round, suggesting that they are influenced by FSGD. The seawater near the back of the cave was supersaturated with respect to atmospheric CO2 nearly year‐round and there is a strong positive divergence from its regional open‐water thermal dependence, which suggests that FSGD is also a source of atmospheric CO2 in this region. Comparison of TA, salinity and pCO2 from the back of the sea cave to their corresponding values from an abrasion platform monitoring site, ca. 3 km south of the cave, suggests that FSGD is occurring along the entire shoreline in this region. Thus, despite the increased productivity due to FSGD mediated nutrient enrichment of adjacent coastal waters of the oligotrophic SEMS, they are still a source of atmospheric CO2 nearly year‐round. Finally, the apparent trends of seawater acidification (ΔpH/Δt = −0.006 yrs−1) and pCO2 increase (+8 ppmV yr−1) observed at the nearby monitoring site since 2013 are explained by increased groundwater recharge and resulting FSGD total alkalinity compared to dissolved inorganic carbon inputs (ΔTA/ΔDIC = 1:1.2).

Assessing impacts of alternative land use strategies on water partitioning, storage and ages in drought‐sensitive lowland catchments using tracer‐aided ecohydrological modelling

AbstractContinuing negative rainfall anomalies, coupled with climate change projections of increased drought severity and frequency, drive an urgent need to increase resilience and integration in land and water management strategies in many regions of the world. However, complex interactions between land cover change, ecohydrological partitioning and water availability are difficult to quantify, especially at different temporal and spatial scales. In conjunction with local stakeholders, we developed plausible, alternative land use scenarios (including forest diversification and agroforestry schemes) based on the existing four primary land use types (i.e., conifer and broadleaved forests, arable agriculture, and pasture) in a 66 km2 drought‐sensitive catchment in northern Germany. We used modelling to evaluate spatial and temporal changes in water flux partitioning, storage and ages. The spatially‐distributed, tracer‐aided ecohydrological model, EcH2O‐iso, calibrated using hydrometric, ecohydrological and isotopic data at daily time steps from 2007 to 2019 was used in this assessment. The results showed that replacing conifer forests with uneven‐aged mixed forests with younger broad‐leaved trees had the greatest potential for reducing total evapotranspiration and increasing groundwater recharge. For coniferous forests, a 50% increase in the proportion of broad‐leaved trees was projected to result in an 11% increase in groundwater recharge across the catchment. The mixed‐forest management alternatives also reduced groundwater turnover times, which would support more rapid recovery of soil moisture and groundwater stores following droughts. This study demonstrates that such an ecohydrological modelling approach has the potential to contribute useful science‐based evidence for policy makers allowing quantitative assessment of potential land use effects on water availability and effective communication with stakeholders.

Evaluating groundwater resources trends through multiple conceptual models and GRACE satellite data.

In this research, three numerical groundwater flow models, developed and calibrated from three equally plausible conceptual models over the Nasia Basin, have been used to assess groundwater resources variations over a transient period. The use of multiple numerical models reduces the effect of uncertainties in conceptual model formulation. All the three calibrated numerical models indicate an increasing trend of groundwater recharge and storage over the period of the groundwater level monitoring. This suggests that the prevailing erratic climatic conditions in the area are conducive for increasing groundwater recharge and storage in the terrain. The high-intensity, short duration rainfall patterns, attending climate change in the basin, enhance high levels of infiltration and percolation, leading to steadily increasing groundwater recharge. Groundwater recharge estimates from each of the models over the transient period appear to reflect the pattern of seasonal variations in rainfall in the region. Data from the models indicates a significant role of baseflow in sustaining perennial streamflow in the area. This presents a significant development in terms of groundwater-based adaptation projects, especially in agriculture. The trend of groundwater recharge in the Nasia Basin is in sync with regional groundwater storage variations estimated from the Gravity Recovery and Climate Experiment (GRACE) satellite data collected and processed over the Volta Basin. At the Volta Basin level, groundwater storage variations indicate a strong positive trend of increasing groundwater recharge from 2002 (beginning of the GRACE mission) to 2022 (end point of the data used for this research). Analysis of the GRACE data suggests that there is a cumulative increase in groundwater storage by 30cm, representing approximately 120 km3 of groundwater over the period in the basin. This translates into approximately 15mm/year of groundwater storage increase. Thus, at both the regional and local levels, groundwater appears to be responding positively to the impacts of erratic rainfall patterns observed in the area recently. The high-intensity, short duration rainfall patterns appear to favor significant groundwater recharge, resulting in a strong positive groundwater storage signal. The high positive groundwater storage signal suggests increasing groundwater resources potential in the area, indicating promising opportunities for groundwater-based climate change adaptation interventions.

A prolonged dry Mid-Holocene recorded by Moon Lake in the Tengger Desert, arid and semiarid China

AbstractReconstructing the Mid-Holocene climate change in arid and semiarid areas can help predict regional moisture availability and resultant lake evolution and vegetation changes due to future warming. Here, we present a sediment core (YLH15A) from Moon Lake in the Tengger Desert, arid and semiarid China. Based on robust accelerator mass spectrometry 14C dating and multiproxy analyses (pollen, grain size, elements, and total organic carbon), we reconstructed regional climate changes since 7.6 cal ka BP. The climate was generally dry from 7.6 to 2.8 cal ka BP, as indicated by the dried-up lake, strong aeolian activities, and no vegetation, except for a short-term wet interval between 5.4 and 4.9 cal ka BP. The generally dry climate shifted after 2.8 cal ka BP, which is suggested by expanded steppe desert/steppe and increased vegetation cover; it was also accompanied by lake development, which was likely related to increased groundwater recharge originating from regional precipitation and temporary floods from adjacent mountain areas. Our results reveal a prolonged dry Mid-Holocene and relatively wet Late Holocene that are basically consistent with climatic records from the central–east Asian arid and hyperarid areas. The prolonged dry climate in the arid and hyperarid areas is likely to be related to high evaporation triggered by high temperatures during the Middle Holocene.

Evaluation of water productivity of smallholder irrigation along a Sand River, in the Maigobo watershed of northern Ethiopia

Sand dams are a type of rainwater harvesting technology that can increase groundwater recharge in dry land environments. They are constructed across seasonal sandy rivers and trap sand and water during floods. The sand acts as a natural filter and storage medium for the water, which can be extracted by the local communities through wells, pumps, or scoop holes. This research aims to evaluate agricultural water productivity based on water consumption (ETa) and biomass production of smallholder irrigation schemes along a sand river with a sand dam in the riverbeds of northern Ethiopia. Remotely sensed satellite data, WaPOR (Water Productivity through Open access of Remotely sensed derived data) database was used to estimate water productivity in the arid and semi-arid area. Following the installation of the sand dam at the irrigated parts of the Mai Gobo watershed, both the annual and seasonal values increased over a number of years, according to the spatial analysis of ETa and biomass production. For instance, the maximum seasonal ETa before the dam was about 70 mm/season, whereas after the dam the spatially analysed ETa reached 174 mm/season. Likewise, maximum seasonal biomass production of 1117 kg/ha and 4433 kg/ha were obtained before and after the construction of the sand dam, respectively. Agricultural water productivity at the irrigated plots of the Mai Gobo watershed was also improved from 1.4 kg/m3 to 2.9 kg/m3 before and after the sand dam respectively. Generally, the output of the study can be used as an input for the concerned stakeholder to take measures against the water scarcity problem in the study area. The study also contributes to the scientific knowledge and understanding of the hydrological and agronomical impacts of the sand dam in the arid and semi-arid regions.

WEAP Model Based Evaluation of Future Scenarios and Strategies for Sustainable Water Management in the Chennai Basin, India

Abstract The gap between water supply and demand is increasing in several urban clusters of the world. This study uses the water evaluation and planning model to assess the water supply and demand dynamics in one of the large metropolitan regions of the Chennai hydrological basin. The primary water supply sources, including reservoirs, groundwater, inter-basin transfer, and desalination plants, were integrated into the model to simulate the current and future water demand and supply scenario. Three rainfall scenarios (excess, normal, and deficit) were utilized to assess their impacts on water supply. The study highlights the increase in unmet demand for normal and deficit rainfall scenarios. In response, various mitigation options were explored, including increasing groundwater recharge, reservoir capacity enhancement, water treatment plant expansion, additional storage, and utilization of water stored in rock quarries. The findings provide valuable insights for policymakers and stakeholders to develop sustainable water management strategies in the Chennai Basin.

MULTIPLE BENEFITS OF REVITALIZING THE ANCIENT WATER-WORKS

Drawing water from rivers tens of kms away or more than hundred meters depth, cannot go on with increasing frequency for long. Therefore, the well-known principle to catch water where it falls practiced in ancient times as seen in thousands of ancient waterworks spread across the country, should be revived. These systems were built centuries or even millennia before, are reusable even now, but concerted effort to revive them must be undertaken. Most of these are in heritage cities and towns and are swamped by urban landscapes. The arterial system of catchment often gets clogged up due to such development activities and the ancient water works becomes obscure and goes into oblivion. The water works which in its functional period may have catered for thousands of denizens in the vicinity as well as enriched the ecosystem and aesthetics of the area, that existed as a prototype for others to see and imitate, is fading off from public knowledge. The present article brings to fore many different types of water works across the millenniums not only to show the wisdom of the earlier people but also revival of such mechanism and replication of these would not only improve availability of water locally but also help increase groundwater recharge, growth of vegetation nearby, general aesthetics, and perhaps even tourism possibilities.

Climate Change and Its Impact on Crop Water Requirement of Mulberry (Morus spp., Moraceae) Crop in Yadgir District, Karnataka, India

This study was carried out to examine trends in crop water requirement under several climate change scenarios to provide projections of changes in crop water requirement of mulberry. According to Indian Network for Climate Change Assessment (INCCA) and Inter-Governmental Panel for Climate Change (IPCC), scenarios which may be included for assessment were developed from their reports. A CROPWAT-8.0 model was utilized to determine the required water requirements for crops in a variety of climate change scenarios. The estimated and demonstrated growing and reducing trend in crop water requirements of Mulberry over the last 35 years was seen in the Yadgir district in overall displayed. As regards Mulberry, there has been a rising ETc tendency in all study area even if different climate change scenarios are used. It was found that climate variability has an impact on the Mulberry crop's water needs. To help address this, it was suggested that to reduce the risk of yield loss due to changing water availability, water conservation efforts such as rainwater harvesting, soil and water conservation, and increased ground water recharge should be implemented in the study area.

Assessing impacts of climate variability and land use/land cover change on the water balance components in the Sahel using Earth observations and hydrological modelling

Study regionSenegal river (SRB), Niger river (NRB), and Lake Chad basins (LCB). Study focusWe investigated the impacts of land use/land cover change (LULC) and climate variability on the water balance components from 1990 to 2020. We applied the Soil and Water Assessment Tool (SWAT) coupled with remote sensing retrievals of actual evapotranspiration (ETa) and surface soil moisture (SSM). To separate the impacts of the two aforementioned factors, two numerical experiments were designed: (i) climate variability effects by applying frozen LULC while changing the climate; (ii) LULC change impacts by applying frozen climate while changing LULC. New hydrological insights for the regionOverall, at the basin level, the results indicated that climate variability had the dominant role in increasing groundwater recharge, surface runoff, groundwater return flow and lateral flow in LCB and SRB. These increases triggered the recovery of lake area and higher water table in LCB and increased in SRB streamflow, while water scarcity increased in NRB. In contrast, the separate effect of LULC change, specifically natural vegetation expansion, increased actual ET and decreased the surface runoff, which could be a reason for lake area depletion in LCB and decreasing SRB and NRB streamflow. At the sub-basin level, LULC change, i.e. a gain in cropland and urban areas at the expense of forests in some sub-basins in NRB, led to a local increase in surface runoff. This implies a better redistribution of water in downstream and compensates the deficit in surface runoff caused by natural vegetation expansion in some other catchments. These changes, simultaneously with high intensity and long-duration precipitation, may increase the likelihood of inundation in some small catchments in the Niger river basin. These outcomes give useful hydrological insights into water and land management by emphasizing the crucial role of water recycling.

Design and Performance Evaluation of Constant Head Double Ring Infiltrometer at H.S.T.U.

An indication of soil that allows water to penetrate into the soil profile is infiltration. Increased ground water recharge is aided by increased filtering rate. The purpose of this study was to assess the soils' infiltration qualities in H.S.T.U. With a constant water head double ring infiltrometer with inner ring of 15 cm, outer ring of 30 cm, and a height of 27 cm was designed. To assess soil texture class, electrical conductivity, pH, and moisture content, soil samples were taken using an auger at a depth ranging from 0 to 15 cm from 5 different chosen locations. Infiltration rates were discovered utilizing a constant head double ring infiltrometer to be 17.53 mm/hr, 13.53 mm/hr, 21.34 mm/hr, 22.4 mm/hr, and 16.21 mm/hr. Sand was present in proportions of 61.2%, 54.2%, 63.2%, 67.2%, and 55.2%. The highest percentage of sand was discovered in location L-4. The percentage of silt was found 26.4%, 26.4%, 20.4%, 22.4% and 34.4% accordingly. 12.4%, 14.4%, 11.4%, 10.4%, and 10.4% of the total weight was clay, respectively. The percentage of water content in soil at five different places was 14.74%, 14.12%, 14.62%, 8.62%, and 11.6%, respectively. The findings show that the research field contains the highest percentage of sand and that the penetration rate is also the highest there. Also, showed a proportionate association between infiltration rate and percentage of sand and a negatively proportional relationship with silt, clay particles, and soil moisture content. The average soil infiltration rate for the HSTU campus area was 18.202 mm/hr.

Impact of land cover changes on Long‐Term Regional‐Scale groundwater recharge simulation in cold and humid climates

AbstractIn cold and humid climates, warming temperatures will result in longer growing seasons, leading to land cover changes that could have long‐term impacts on groundwater recharge (GWR), in addition to the direct impacts of climate change. The objective of this study was therefore to investigate whether land cover (LC) changes need to be considered when simulating long‐term regional‐scale potential GWR in cold and humid climates by (1) quantifying how LC changes impact simulated GWR and (2) quantifying the combined impacts of LC and climate changes on the future GWR changes. Using the region of southern Quebec (Canada) as a case study and a water budget model, this work proposes an innovative coupling of land cover change scenarios and specific future climate conditions to simulate spatially distributed transient GWR over the 1951–2100 period. The results showed that including LC changes in long‐term GWR simulations produced statistically significant increases in GWR compared to using a constant LC through time (average of +13 mm). Massive afforestation taking place on agricultural lands simulated for one of the scenario chains (RCP4.5) increased GWR by reducing runoff during the snow‐dominated period (average − 17 mm). The results also showed that GWR was more sensitive to climate change for scenarios that included intense land cover changes. Additionally, the spatial distribution of the LC changes influenced their simulated impacts on GWR. Considering that the methodology was computationally feasible and entirely transferrable to the new CMIP6 ensemble, LC changes should be considered systematically in long‐term groundwater resources simulations.

Thicketized oak woodlands reduce groundwater recharge

Woodlands and pastures across the Post Oak Savannas (POS) in Texas have been undergoing thicketization over the last century via encroachment by understory shrubs such as Yaupon (Ilex decidua, Ilex vomitoria) and expansion of eastern redcedar (Juniperus virginiana). Because a large part of POS overlies the Carrizo-Wilcox (CW) aquifer – the third most important aquifer in Texas, there is a strong incentive to identify opportunities to increase groundwater recharge through land management. The purpose of this research is to evaluate the influence of thicketization of post oak (Quercus stellata) stands on deep drainage (DD) in POS. We achieved this by, a) applying chloride mass balance on soil cores, and b) simultaneously monitoring soil moisture in a woodland pasture setting in POS. Four sites representing different vegetation covers were identified for sampling: 1) a thicketized oak woodland paired with an adjacent open site, 2) a woodland mosaic, 3) a pasture and 4) a pine-oak stand paired with an adjacent open site. A total of 24 soil cores to the depth of 260 cm were collected and (soil) pore water chloride concentrations at multiple depths were measured. Soil moisture was monitored at 21 locations, to the depth of 140–260 cm using a neutron moisture meter. Negligible DD was estimated in the thicketized woodland, whereas most open locations recorded 3–18 cm/year and the woodland mosaic 0–1 cm of DD. Soil moisture data, collected from Jul-2020 to Jun-2021 also suggested higher deep drainage fluxes under open areas – with occurrence of sub-surface saturation only under the open areas and never under the woodlands. These results suggest that the thicketization in oak savannas is substantially reducing groundwater recharge. Given the extent of thicketized oak savannas across United States, this could be impacting water budgets and groundwater recharge rates on regional scales.

Combined geophysical and hydrological study on climatic factors variability and their effect on aquifer productivity and recharge in Obubra, Cross River state

Combined techniques of geophysics, hydrology and hydrogeology were employed in the estimation of groundwater recharge. Effects of meteorological factors on groundwater recharge were critically explored. Using tritium tagging and electrical resistivity techniques groundwater recharge was estimated. VES data was obtained from 16 stations, each with a traverse length of 500 m and inter station distance of 800m. Both the wet and dry season saw the completion of Tritium tagging surveys at every site. The study also looked at how weather conditions effected the stations aquifers productivity and recharge. The study found that rising rainfall causes an increase in groundwater recharge. The episodic variations in rainfall during period match with the patterns of groundwater recharge variation (1988-2018). The study also revealed a positive association between rainfall and groundwater recharge with a correlation coefficient of 0.9 but a negative correlation between groundwater recharge, temperature and evaporation with correlation coefficients of -0.52 and -0.42. But when the three climatic variables were combined with groundwater, the regression analysis revealed a multiple coefficient of determination of 0.821 percent (R²= 82.1 percent). Tritium tagging technique show that the recharge estimate in the study area varies between 6 and 19 percent. The study also revealed a linear relationship between electrical resistivity of the top soil and the estimated recharge.

KAJIAN AWAL PEMBUATAN BETON POROUS UNTUK PAVING BLOCK RAMAH LINGKUNGAN

In heavily populated urban areas, high rainfall can cause inundation and even flooding because the catchment area is decreasing. To reduce rainwater runoff and increase groundwater recharge, porous concrete can be used in housing area, in parking lots and roads with low traffic loads. Porous concrete is an environmentally friendly and sustainable building material. This study aims to examine the effect of aggregate composition on the porosity and tensile strength of porous concrete. The composition of the concrete mixture is determined based on the weight ratio between portland cement type I (PC) and coarse aggregate (AK), i.e. 1 PC : 3 AK, 1 PC : 4 AK, and 1 PC : 5 AK and the ratio of fine aggregate weight (AH) of 0 ; 0.5 ; 1, and the w/c is 0.5. For each variation, six 150 mm cubes were made. The parameters tested were slump, volume weight, porosity and compressive strength at day 28. The results show that the more coarse aggregate, the lower the volume weight and its compressive strength, and the higher the porosity and slump. Fine aggregate addition increases the compressive strength and volume weight and decrease slump value and porosity. The highest slump value (205 mm) and the smallest volume weight and compressive strength were obtained from concrete mixture with PC/AK=1/5 without AH content. The smallest slump (170 mm) and porosity values were obtained from concrete mixture with PC/AK=1:3 and AH/AK=1 and the largest volume weight and compressive strength. In this study, the slump value tends to be directly proportional to porosity and inversely proportional to volume weight and compressive strength. For further research, it is recommended that the w/c value be reduced to get a larger porosity value but without a significant decrease in compressive strength.

Impacts of climate change on Swiss alluvial aquifers – A quantitative forecast focused on natural and artificial groundwater recharge by surface water infiltration

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.

Enhancement of Groundwater Recharge from Wadi Al Bih Dam, UAE

Groundwater and harvested rainwater represent the only conventional freshwater resources in the United Arab Emirates (UAE). Groundwater resources in Wadi Al Bih, UAE, are sustainable due to the low exploitation rate for domestic and agricultural purposes. Thus, the groundwater depletion in this area is far less than in other parts of the country. The Wadi Al Bih area is very important for achieving water security in UAE. Therefore, the possible measures of increasing groundwater recharge (e.g., managed aquifer recharge (MAR) methods) are investigated in this paper. The available water resource data were collected, reviewed, validated, and stored in a GIS database. Then, a GIS-based water budget model (WBM) was developed to evaluate the available groundwater resources in Wadi Al Bih and recharge sources. The analyses showed that only 49% of the accumulated rainwater behind the dam is recharging the underlying aquifer. Due to the absence of any direct recharge techniques, the remaining 51% is lost by direct evaporation (15%), and as soil moisture increases in the unsaturated zone (36%), it will subsequently evaporate or percolate depending on the precipitation pattern and air temperature. The results of the WBM indicated that the freshwater resources were decreasing at an alarming rate of approximately thirty-five million cubic meters (MCM) per year until 2019. The groundwater storage and salinity were governed by the rates and patterns of precipitation. For example, the recharge resulting from the two consecutive maximum monthly precipitation events in December 2019 and January 2020 has significantly increased the fresh groundwater reserve and slightly retreated the saline/brackish water toward the shoreline. Moreover, a Mann–Kendall trend analysis was conducted to assess the influence of precipitation, temperature, and evaporation on groundwater recharge. The outcomes suggested that climate variables had a significant effect on groundwater supplies. The mitigation measures include revising groundwater withdrawal rates based on the annual recharge and enhancing recharge using different MAR techniques and dam operation plans.

The impacts of LULC and climate change scenarios on the hydrology and sediment yield of Rib watershed, Ethiopia.

Watershed-scale hydrology and soil erosion are the main environmental components that are greatly affected by environmental perturbations such as climate and land use and land cover (LULC) changes. The purpose of this study is to assess the impacts of scenario-based LULC change and climate change on hydrology and sediment at the watershed scale in Rib watershed, Ethiopia, using the empirical land-use change model, dynamic conversion of land use and its effects (Dyna-CLUE), and soil and water assessment tool (SWAT). Regional climate model (RCM) with Special Report on Emission Scenarios (SRES) and Representative Concentration Pathway (RCP) outputs were bias-corrected and future climate from 2025 to 2099 was analyzed to assess climate changes. Analysis of the LULC change indicated that there has been a high increase in cultivated land at the expense of mixed forest and shrublands and a low and gradual increase in plantation and urban lands in the historical periods (1984-2016) and in the predictions (2016-2049). In general, the predicted climate change indicated that there will be a decrease in precipitation in all of the SRES and RCP scenarios except in the Bega (dry) season and an increase in temperature in all of the scenarios. The impact analysis indicated that there might be an increase in runoff, evapotranspiration (ET), sediment yield, and a decrease in lateral flow, groundwater flow, and water yield. The changing climate and LULC result in an increase in soil erosion and changes in surface and groundwater flow, which might have an impact on reducing crop yield, the main source of livelihood in the area. Therefore, short- and long-term watershed-scale resource management activities have to be designed and implemented to minimize erosion and increase groundwater recharge.

Response of groundwater to different water resource allocation patterns in the Sanjiang Plain, Northeast China

Study regionThe Sanjiang Plain, located at the confluence of Heilong, Songhua, and Wusuli Rivers, Northeast China. Study focusDue to the low and flat terrain, wetlands and swamps were widely distributed in plain areas in history. After decades of reclamation, farmland has replaced wetland as the dominant landscape. The competition of water resources between wetland ecological health and food security is very fierce, which is mainly reflected in the serious overexploitation of groundwater. This study used a new coupled surface water-groundwater model with an innovative function of irrigation and drainage simulation to research the changes of groundwater in the Sanjiang Plain under different water resource allocation schemes and paddy development scale in the future, which may provide a scientific basis for the planning of water resource allocation projects related to the restoration of groundwater and wetlands in this region. New hydrological insights for the regionWe established four prediction models for different water resource allocation schemes and paddy areas by replacing the water supply data and planting structure of the baseline model in the Sanjiang Plain. By comparing the groundwater balance and level of various schemes simulated by prediction models, it was found that the complete water diversion scheme covering the plain areas would greatly reduce groundwater exploitation, increase groundwater recharge, and turn groundwater storage from deficit to surplus, which would increase by 853 million m3/a. It would gradually compensate for the historical debts due to groundwater overexploitation while achieving a balance between groundwater recharge and discharge; thus, the groundwater depth in most part of the plain areas would be restored to less than 5 m. However, the scheme also had a defect, that is, it may cause soil secondary salinization in shallow groundwater areas. Therefore, the scheme needs to be further optimized to make full use of the low-cost groundwater.

Improving groundwater sustainability through conservation strategies in a critical-prohibited coastal plain

Over-abstractions of groundwater resources influence the ecology and sustainability of groundwater resources. In this study, we examined the effectiveness of various conservations strategies to improve the sustainability of groundwater resources in the critical-prohibited plain of Behshahr-Bandar-e-Gaz in the coastal area of northern Iran. The soil and water assessment tool (SWAT) was employed to examine this case. Calibration and validation of the model were done using flow data of the periods of 2007–2013 and 2014–2017, respectively, after analyzing the model's sensitivity. We simulated the groundwater table by determining the volume of recharge per hydrological response units (HRUs). The calibrated model was then applied to assess various management scenarios, including agroforestry (Agro-S1, Agro-S2, Agro-S3), no-tillage (NOT), conservation tillage (CST), rice straw mulch (RSM), and wheat Straw mulch (WSM). Sensitivity analysis revealed 14 parameters as the most sensitive parameters. The Nash-Sutcliffe Efficiency (NSE) and determination coefficient (R2) of 0.56–0.93 and 0.74 to 1.00 in the calibration stage and 0.56 to 0.84 and 0.66 to 0.92 in the validation stage, respectively, indicated the acceptable capability of the model in flow simulation. The model also showed acceptable performance in groundwater table simulation with NSE and R2 of 0.76 and 0.88, respectively. RSM scenario was considered the most effective conservation strategy as it reduced surface runoff by 27.22% and ultimately, increased soil water content (by 6.02%) and groundwater recharge (by 23.52%). Furthermore combined scenarios (RSM, NOT, and Agro_S3) were the best conservation methods among the scenarios that indicated a decrease of 18.64% in surface runoff and an increase of 4.92% in infiltration, 4.61% in total groundwater recharge, and 1.76% of soil water content (green water). The RSM scenario improved the sustainability of groundwater resources in the region by 17.5%. An additional improvement (5.4%) was achieved through a combined scenario. These changes were generally made in the form of increasing the most the essential components of the water balance. Furthermore, the combination of Agro-S3, RSM and, NOT scenarios was the most effective ones to increase groundwater recharge in the region. Based on the results, although complete restoration of prohibited-critical aquifers is almost impossible, relative stability can be achieved by adopting a combination of different effective management measures.

A century of groundwater accumulation in Pakistan and northwest India

The groundwater systems of northwest India and central Pakistan are among the most heavily exploited in the world. However, recent, and well-documented, groundwater depletion has not been historically contextualized. Here, using a long-term observation-well dataset, we present a regional analysis of post-monsoon groundwater levels from 1900 to 2010. We show that human activity in the early twentieth century increased groundwater availability before large-scale exploitation began in the late twentieth century. Net groundwater accumulation in the twentieth century, calculated in areas with sufficient data, was at least 420 km3 at ~3.6 cm yr–1. The development of the region’s vast irrigation canal network, which increased groundwater recharge, played a defining role in twentieth-century groundwater accumulation. Between 1970 and 2000, groundwater levels stabilized because of the contrasting effects of above-average rainfall and the onset of tubewell development for irrigation. Due to a combination of low rainfall and increased tubewell development, approximately 70 km3 of groundwater was lost at ~2.8 cm yr–1 in the first decade of the twenty-first century. Our results demonstrate how human and climatic drivers have combined to drive historical groundwater trends.