Mean Annual Groundwater Recharge Research Articles

Average monthly recharge, surface runoff, and actual evapotranspiration estimation using WetSpass-M model in Low Folded Zone, Iraq

Abstract The evaluation of the spatial and temporal distribution of groundwater recharge is required to develop the regional groundwater model for more precise simulations of various management scenarios. WetSpass-M (Water and Energy Transfer between Soil, Plants, and Atmosphere under Steady-State Conditions), which is a GIS-based spatially distributed water balance model, is deployed to evaluate monthly groundwater recharge, surface runoff, and actual evapotranspiration in the Low Folded Zone from 2000 to 2019. ArcGIS software prepares the essential relevant input data for the Wetspass-M model as grid maps. They include monthly climatological measurements (precipitation, temperature, and wind speed), land cover distribution, soil map, groundwater depth, topography, and slope. The mean annual groundwater recharge, evapotranspiration, and runoff were found to be 128, 131, and 72 mm, respectively. Accordingly, recharge accounts for 39% of the precipitation, while the rest, 40 and 21%, become evapotranspiration and surface runoff, respectively. WetSpass-M model results are meant to enable integrated groundwater modeling. The study of simulation data demonstrates that the WetSpass-M model accurately simulates the hydrological water budget components of the Low Folded Zone. In addition, a better understanding of the simulated spatial and temporal distribution of water balance components is beneficial for managing and planning the available water resources of the Low Folded Zone in Iraq, which faces water scarcity threats.

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

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

Estimation of shallow groundwater abstraction for irrigation and its impact on groundwater availability in the Lake Tana sub-basin, Ethiopia

Study regionLake Tana sub-basin of the Upper Blue Nile River Basin, Ethiopia Study focusGroundwater use for small-scale irrigation is increasing in the Lake Tana sub-basin. However, the abstraction amount and its impact are not well understood. In this study, a new methodological approach was utilized to estimate the irrigation water abstraction amount, which is based on groundwater level monitoring before, during, and at the end of the irrigation season (2021/2022). The monitoring was conducted on 361 hand-dug wells distributed throughout the sub-basin, which is subdivided into East, Southwest, and North zones. New hydrological insights for the regionGroundwater abstraction for irrigation and associated groundwater level decline estimates are 10.6 × 106 m3 and 2.43 m in the East, 4.2 × 106 m3 and 3.23 m in the Southwest, and 0.6 × 106 m3 and 1.32 m in the North. These abstractions account for 103%, 97%, and 62% of the mean annual groundwater recharge in the East, Southwest, and North zones, respectively. Groundwater is overexploited in the East and Southwest zones although, at the sub-basin scale, the amount of groundwater used for irrigation is small compared to the renewable groundwater resource. However, if groundwater-based irrigation continues to expand especially in the East and Southwest zones, groundwater scarcity at the local scales will worsen. Adaptive management strategies are required to minimize the potential adverse effects on groundwater resources.

Comparison of the groundwater recharge estimations of the highly exploited aquifers in Bangladesh and their sustainability

Sudden increase of groundwater abstraction for water supply to a million forcefully migrated Myanmar nationals (Rohingya) in Ukhia and Teknaf Upazila of Cox's Bazar district has created a threat to the sustainability of the Dupi Tila and Tipam aquifers, the primary source of drinking water for the host community. Reasonable estimation of groundwater recharge is crucial for understanding the sustainability of an aquifer. Therefore, this study, estimates groundwater recharge employing multiple methods such as (i) WetSpass water balance model, (ii) Water Table Fluctuation (WTF), (iii) Chloride Mass Balance (CMB), and (iv) Empirical Formulas (EF) and compares it with current withdrawal. Additionally, the applicability of empirical formulas for recharge estimation in Bangladesh has been evaluated, which will benefit future groundwater studies requiring a rapid estimate of recharge from precipitation. Despite a large spatial variability in recharge, the spatially mean annual groundwater recharge estimated by these methods is comparable to each other. The estimated spatially mean annual volumetric groundwater recharge for the Dupi Tila and Tipam aquifer is 135 and 122 million m3/y, respectively. Most of the estimated groundwater abstraction of 49 million m3/y in this area is from the Dupi Tila aquifer, which is about 36% of the annual recharge suggesting that the current withdrawal should be sustainable. However, since the Rohingya camp abstraction is concentrated within a small area, there is potential for a large cone of depression development in and around the camp, which may adversely impact the wells of the host population in adjacent areas. A numerical model is required to assess the extent of the cone and its impacts on host community wells. This study also finds that the Maxey-Eakin and Sehgal formulas for precipitation-based recharge estimation are the most suitable for this area and may be applied in other areas of Bangladesh.

Groundwater recharge evaluation due to climate change using WetSpass-M distributed hydrological model in Bilate river basin of Ethiopia

Sporadic change in climate is altering the hydrologic processes affecting the groundwater recharge (GWR) systems across the planet. Distributed groundwater recharge (DGWR) is studied in the Bilate river basin of Ethiopia to predict the current and future for long-term groundwater utilization, planning and management. Precipitation and temperature were acquired from the Coordinated Regional Climate Downscaling Experiment (CORDEX) Africa platform using RCP4.5 and RCP8.5 scenarios for the periods 1986–2015, 2041–2070, and 2071–2100. WetSpass-M distributed hydrological model was used to analyze the seasonal and annual GWR under varying amplitude and dispersion. Particularly in the spring and summer, due to increase in temperature and scanty rainfall GWR is severely affected. Average minimum and maximum temperatures are anticipated to rise by 0.11 °C–0.61 °C and 0.75°C–2.15 °C respectively during mid-RCP4.5 and long-term RCP8.5 scenarios. For the baseline period, RCP4.5, and RCP8.5 for both mid-term and long-term periods, the maximum annual GWR was predicted to be 442.5 mm/yr, 371.6 mm/yr, 347.6 mm/yr, 319.6 mm/yr, and 327.41 mm/yr, respectively. The maximum annual GWR is decreased by 83.3 mm–138.7 mm in the RCP4.5 scenario during the years 2041–2071, but in the RCP8.5 scenario during the years 207–2100, the maximum annual GWR is decreased by 26.1 mm–72.3 mm, while the mean annual GWR is decreased by 26.1 mm–72.3 mm. There have been numerous studies about how climate change (CC) may affect GWR, but this study focuses specifically on forecasting precipitation and temperature to determine GWR in the basin. The results could be crucial for suitable water management use by interpreting the direct and indirect effects of climate change on recharge systems.

Analysis of Groundwater Recharge in Mongolian Drylands Using Composite Vadose Zone Modeling

Knowledge of groundwater recharge (GR) is important for the effective management of water resources under semi-arid continental climates. Unfortunately, studies and data in Mongolia are limited due to the constraints in funding and lack of research infrastructures. Currently, the wide accessibility of freely available global-scale digital datasets of physical and chemical soil properties, weather data, vegetation characteristics, and depths to the water table offers new tools and basic information that can support low-cost physically based and process-oriented models. Estimates of GR over 41 study sites in Mongolia were obtained using HYDRUS-1D in a 2-m-thick soil profile with root depths of either 0.30 or 0.97 m by exploiting the daily precipitation and biome-specific potential evapotranspiration values. The GR simulated by HYDRUS-1D arrives at the water table and becomes the actual GR with a lag time that has been calculated using a simplified form of the Richards equation and a traveling wave model. The mean annual precipitation ranges from 57 to 316 mm year−1, and on average about 95% of it is lost by mean annual actual evapotranspiration. In the steppe region, the vegetation cover induces higher-than-normal actual transpiration losses and consequently lower GR. The mean annual GR rates span between 0.3 and 12.0 mm year−1, while travel times range between 4 and 558 years. Model prediction uncertainty was quantified by comparing actual evapotranspiration and GR with available maps and by a sensitivity assessment of lag time to the soil moisture in the deep vadose zone. The partial least squares regression (PLSR) was used to evaluate the impact of available environmental properties in explaining the 47.1 and 59.1% variability of the spatially averaged mean annual GR and travel time, respectively. The most relevant contributors are clay content, aridity index, and leaf area index for GR, and depth to the water table and silt content for the lag time. In data-poor, arid, and semi-arid regions such as Mongolia, where the mean annual GR rates are low and poorly correlated to precipitation, the ever-increasing availability of world databases and remote sensing products offers promise in estimating GR.

Assessment of Water Balance Components by Using Wetspass Model: The Case of Dengego Sub-basin, Eastern Ethiopia

The search for new water resources, as well as the development of water balance models that can be used to control and manage the resource, is at the heart of the search for new water resources in eastern Ethiopia, particularly in the Dengego sub-basin, and its socio-economic significance in terms of water demand for agriculture and domestic use. The water balance components of the Dengego sub-basin were investigated using the WetSpass hydrological model. The goal of this study is to assess the water balance components in the Dengego sub-basin. According to WetSpass, the mean annual evapotranspiration, surface runoff, and groundwater recharge were 494.2, 173.6, and 20.2 mm, respectively. Actual evapotranspiration and surface runoff accounted for 25.2 percent and 71.8 percent of precipitation, respectively and recharge made up 2.9 percent of precipitation. Annually 7.3 million m3 of water recharges into the groundwater table as recharge from the precipitation on the entire watershed.The contribution of this study could be used as baseline information for regional water resource experts, policy makers and researchers for further investigation. It can also be concluded that integrated WetSpass and GIS-based models are good indicators for estimating and understanding of water balance components in a given watershed to implement an integrated watershed management plan for sustainable utilization and sustainable development.

Changing Water Resources Under El Niño, Climate Change, and Growing Water Demands in Seasonally Dry Tropical Watersheds

AbstractThe wet‐dry tropics of Central America are characterized by long dry seasons, during which communities often struggle for water. High interannual rainfall variability, driven in parts by the El Niño Southern Oscillation (ENSO), increases these challenges. Further, climate change projections indicate that the region will likely become drier. However, research on impacts on water resources at the watershed scale is limited in the region—yet this information is essential for water managers. Therefore, in this research, we quantified the potential impacts of ENSO and four different climate change scenarios on water resources in two watersheds in the wet‐dry tropics of Guanacaste, Costa Rica, using a hydrological model (Water Evaluation and Planning Tool [WEAP]). Given that the watersheds are human used, we also explored different water demand scenarios. Modeling results indicated that an extreme El Niño can reduce groundwater recharge and streamflow by ∼60% relative to ENSO neutral. For 2075–2100, modeling results indicated that while potential evapotranspiration increases, actual evapotranspiration decreases due to limited water availability. Further, climate change may lead to reductions of mean annual streamflow and groundwater recharge by 40%–45% and 26%–28%, respectively, in comparison to the historical baseline. Importantly, high population growth could further hasten potentially irreversible groundwater storage declines. On the other hand, reduction of per‐capita water demand could slow down, or even reverse, the decline of groundwater storage.

Using baseflow to quantify diffuse groundwater recharge and drought at a regional scale

Although diffuse groundwater recharge is difficult to quantify at a regional scale, baseflow discharge can be used in watersheds with gaining streams with negligible effects from pumping. In Iowa, where these conditions are met, we investigated how watershed-scale baseflow calculated from a network of 132 streamflow gages can be used to quantify spatial and temporal patterns of groundwater recharge across a region; and characterize the emergence and expansion of drought conditions in the state. Mean annual groundwater recharge for the 2000–2017 study period estimated by area-weighting annual baseflow was found to be approximately 220 mm but vary widely from 73 to 467 mm based on precipitation inputs. Recharge was found to be particularly concentrated in the months of March to July which accounted for 66% of the average annual recharge. Baseflow discharged from the drought-impacted headwater basins was highly correlated to U.S. Drought Monitor designations in Iowa headwater basins and thresholds varied among landscape regions due to differences in soils and hydrology. Economic losses due to drought were found to substantially increase when annual groundwater recharge was less than approximately 130 mm yr−1. Overall, study results suggest that regional groundwater recharge and drought susceptibility can be reliably assessed using baseflow available from networked stream gages.

Testing Evapotranspiration Estimates Based on MODIS Satellite Data in the Assessment of the Groundwater Recharge of Karst Aquifers in Southern Italy

In many Italian regions, and particularly in southern Italy, karst aquifers are the main sources of drinking water and play a crucial role in the socio-economic development of the territory. Hence, estimating the groundwater recharge of these aquifers is a fundamental task for the proper management of water resources, while also considering the impacts of climate changes. In the southern Apennines, the assessment of hydrological parameters that is needed for the estimation of groundwater recharge is a challenging issue, especially for the spatial and temporal inhomogeneity of networks of rain and air temperature stations, as well as the variable geomorphological features and land use across mountainous karst areas. In such a framework, the integration of terrestrial and remotely sensed data is a promising approach to limit these uncertainties. In this research, estimations of actual evapotranspiration and groundwater recharge using remotely sensed data gathered by the Moderate Resolution Imaging Spectrometer (MODIS) satellite in the period 2000–2014 are shown for karst aquifers of the southern Apennines. To assess the uncertainties affecting conventional methods based on empirical formulas, the values estimated by the MODIS dataset were compared with those calculated by Coutagne, Turc, and Thornthwaite classical empirical formulas, which were based on the recordings of meteorological stations. The annual rainfall time series of 266 rain gauges and 150 air temperature stations, recorded using meteorological networks managed by public agencies in the period 2000–2014, were considered for reconstructing the regional distributed models of actual evapotranspiration (AET) and groundwater recharge. Considering the MODIS AET, the mean annual groundwater recharge for karst aquifers was estimated to be about 448 mm·year−1. In contrast, using the Turc, Coutagne, and Thornthwaite methods, it was estimated as being 494, 533, and 437 mm·year−1, respectively. The obtained results open a new methodological perspective for the assessment of the groundwater recharge of karst aquifers at the regional and mean annual scales, allowing for limiting uncertainties and taking into account a spatial resolution greater than that of the existing meteorological networks. Among the most relevant results obtained via the comparison of classical approaches used for estimating evapotranspiration is the good matching of the actual evapotranspiration estimated using MODIS data with the potential evapotranspiration estimated using the Thornthwaite formula. This result was considered linked to the availability of soil moisture for the evapotranspiration demand due to the relevant precipitation in the area, the general occurrence of soils covering karst aquifers, and the dense vegetation.

Variability in spatial–temporal recharge under the observed and projected climate: A site-specific simulation in the black soil region of Russia

The main purpose of this work is to evaluate diffuse groundwater recharge and its temporal dynamics at sites with different landscapes and soil profiles under observed and projected climate variability. Three typical sites with different landscapes and topsoil profiles were chosen for the field study. Field work consisted of pit development and soil sample collection for laboratory study using the centrifuge method. Soil hydraulic parameters were obtained by the RETC code using the observed values of volumetric water content vs. pressure head. HYDRUS-1D code was used to estimate groundwater recharge based on a 70-year (1945–2015) meteorological dataset with daily resolution (including values of precipitation, air temperature, wind speed, and humidity). This dataset was preprocessed using our SURFBAL code to calculate the surface and topsoil water and energy balance. Retrospective historical simulation results showed that there was a considerable variation in the mean annual groundwater recharge values (49–104 mm/year) for the three studied profiles. The temporal change in groundwater recharge occurred relatively synchronously at all sites and was governed by the change in the current annual aridity index. The results of this historical simulation did not reveal any traces of climate change in the groundwater recharge of the studied region in the last 30–40 years. To predict the recharge variations in the second half of the 21st century, the LARSWG forecast weather generator with the climate projections of the 5th General Circulation Models (GCMs) from the Coupled Model Intercomparison Project 5 (CMIP5) family was used. On average in the case of climate development under the maximum greenhouse gas emissions RCP8.5 scenario, there will be a reduction in groundwater recharge in the studied region in 2060–2080, caused by two factors: change of aridity index, which determines evapotranspiration during a warm season and the accumulation of snow and subsequent meltwater infiltration during the snowmelt periods.

Simulating Land Cover Change Impacts on Groundwater Recharge under Selected Climate Projections, Maui, Hawaiʻi

This project developed an integrated land cover/hydrological modeling framework using remote sensing and geographic information systems (GIS) data, stakeholder input, climate information and projections, and empirical data to estimate future groundwater recharge on the Island of Maui, Hawaiʻi, USA. End-of-century mean annual groundwater recharge was estimated under four future land cover scenarios: Future 1 (conservation-focused), Future 2 (status-quo), Future 3 (development-focused), and Future 4 (balanced conservation and development), and two downscaled climate projections: a coupled model intercomparison project (CMIP) phase 5 (CMIP5) representative concentration pathway (RCP) 8.5 “dry climate” future and a CMIP3 A1B “wet climate” future. Results were compared to recharge estimated using the 2017 baseline land cover to understand how changing land management and climate could influence groundwater recharge. Estimated recharge increased island-wide under all future land cover and climate combinations and was dominated by specific land cover transitions. For the dry future climate, recharge for land cover Futures 1 to 4 increased by 12%, 0.7%, 0.01%, and 11% relative to 2017 land cover conditions, respectively. Corresponding increases under the wet future climate were 10%, 0.9%, 0.6%, and 9.3%. Conversion from fallow/grassland to diversified agriculture increased irrigation, and therefore recharge. Above the cloud zone (610 m), conversion from grassland to native or alien forest led to increased fog interception, which increased recharge. The greatest changes to recharge occurred in Futures 1 and 4 in areas where irrigation increased, and where forest expanded within the cloud zone. Furthermore, new future urban expansion is currently slated for coastal areas that are already water-stressed and had low recharge projections. This study demonstrated that a spatially-explicit scenario planning process and modeling framework can communicate the possible consequences and tradeoffs of land cover change under a changing climate, and the outputs from this study serve as relevant tools for landscape-level management and interventions.

Effect of Land Use/Land Cover Change on Groundwater Recharge in Osun Drainage Basin, Nigeria

Osun drainage basin is one of the regions in Nigeria experiencing increasing population growth and rapid urbanization; and about 70% of the inhabitantsrely on shallow groundwater resources of the region. Change in land use/land cover is one of the significant factors controlling regional hydrology and groundwater resources, thus the continuous change in land use and land cover of the drainage basin will significantly affect the basin’s groundwater resources. There are 7 classified land use/land cover in the study area which are bare surfaces, built up area, crops/shrubs, forest, rock outcrops, water bodies and wetland. Applying WetSpass-M hydrological model, we predicted the effect of land use/land cover change on the groundwater recharge in Osun drainage basin, Nigeria between 1984-2015. The results revealed that the highest groundwater recharge of 48.56%, 33.64% and 37.29% occurred in forested area in 1984, 2000 and 2015, respectively. This result might be due to the influence of vegetation in slowing down the speed of running water across the forest area, that allows more infiltration and deep percolation into the water table to recharge the groundwater system. On the other hand, the least groundwater recharge of the total annual was on the rock outcrops, which are about 4% in 1984, 3% in 2000 and 2% in 2015. The least recharge found on rock outcrops is expected and may be attributed to the fact that infiltration can only occur around or on decomposed rock outcrop, which may result in minute recharge to the groundwater system. The mean annual groundwater recharge of the basin for the land use/land cover of 1984, 2000 and 2015 are476.54, 411.07 and 430.06 mm/y, respectively. Overall, for the 32 years period of investigation, change in land use/land cover accounts for only 10% reduction in mean groundwater recharge occurrence between 1984 and 2015. Also, there is a change in recharge pattern in the study area during this period because most often, change in land use/land cover is a transition from one land use/land cover class to another, and the recharge pattern is influenced based on the degree of transition that took place and the characteristics of the dominant land use/land cover at a particular area of the basin. Although, the 10% reduction in mean annual recharge appears minute, this might become pronounced if the current rate of deforestation in the drainage basin continues unabated. Therefore, proper land use allocation, regulated land development and afforestation in terms of planting of native trees that were lost through anthropogenic activities in the basin should be policy option for groundwater sustainability.

Application of a loose coupling model for assessing the impact of land-cover changes on groundwater recharge in the Jinan spring area, China

The Jinan spring area is one of the fastest developing and most water-stressed regions of China. Because of rapid urban expansion, groundwater recharge has been greatly influenced by land-use/cover change (LUCC). To gain an improved understanding of how the groundwater recharge affected by LUCC from 1960 to 2015, normal years, including 1985, 2000, and 2015, were selected using the Pearson-III distribution. Land-cover types of the normal years were classified using Thematic Mapper images. A loose coupling of an urban expansion model and a hydrological model was used to quantify the impact of LUCC on groundwater recharge. The results showed that land converted to built-up land was mainly mixed forest and arable land. The proportion of land-use types that remained unchanged was generally less than 50%, except for built-up land. In 2030, the area of built-up land will continue to increase, while the area of arable land and mixed forest will decrease correspondingly. The mean annual groundwater recharge was 88.32, 87.95, 73.31, and 76.17 mm for 1985, 2000, 2015, and 2030, respectively, which accounts for 14.01, 12.90, 12.20, and 11.98%, respectively, of the annual precipitation. In the water balance of the study area, only a small fraction (11.98–14.01%) of precipitation recharges the groundwater, and the remainder is lost by evapotranspiration (81.41–82.05%) and to a lesser extent by surface runoff (4.15–6.83%). The amount of groundwater recharge is mainly controlled by precipitation and potential evapotranspiration. Recharge is negatively correlated with the drought index. The ratio of groundwater recharge to precipitation decreased at a rate of − 0.06% from 1985 to 2015. The recharge/precipitation ratio is expected to decrease by a further 0.22% by 2030. The decrease in the ratio is primarily the result of an increase in built-up land areas, and a decrease in mixed forest and arable land areas.

Regionalization with hierarchical hydrologic similarity and ex situ data in the context of groundwater recharge estimation at ungauged watersheds

Abstract. There are various methods available for annual groundwater recharge estimation with in situ observations (i.e., observations obtained at the site/location of interest), but a great number of watersheds around the world still remain ungauged, i.e., without in situ observations of hydrologic responses. One approach for making estimates at ungauged watersheds is regionalization, namely, transferring information obtained at gauged watersheds to ungauged ones. The reliability of regionalization depends on (1) the underlying system of hydrologic similarity, i.e., the similarity in how watersheds respond to precipitation input, as well as (2) the approach by which information is transferred. In this paper, we present a nested tree-based modeling approach for conditioning estimates of hydrologic responses at ungauged watersheds on ex situ data (i.e., data obtained at sites/locations other than the site/location of interest) while accounting for the uncertainties of the model parameters as well as the model structure. The approach is then integrated with a hypothesis of two-leveled hierarchical hydrologic similarity, where the higher level determines the relative importance of various watershed characteristics under different conditions and the lower level performs the regionalization and estimation of the hydrologic response of interest. We apply the nested tree-based modeling approach to investigate the complicated relationship between mean annual groundwater recharge and watershed characteristics in a case study, and apply the hypothesis of hierarchical hydrologic similarity to explain the behavior of a dynamic hydrologic similarity system. Our findings reveal the decisive roles of soil available water content and aridity in hydrologic similarity at the regional and annual scales, as well as certain conditions under which it is risky to resort to climate variables for determining hydrologic similarity. These findings contribute to the understanding of the physical principles governing robust information transfer.

Assessment of Groundwater Recharge, Evaporation, and Runoff in the Drava Basin in Hungary with the WetSpass Model

The assessment of spatial and temporal distribution of groundwater recharge is required as an input to develop the regional groundwater model in the Drava flood plain for more accurate simulations of different management scenarios. WetSpass-M, a GIS-based spatially-distributed water balance model, was implemented to assess monthly, seasonal, and the annual averages of groundwater recharge, surface runoff and actual evapotranspiration in the Drava basin, Hungary for the period between 2000–2018. The basic relevant input-data for the Wetspass-M model is prepared in grid-maps using the tool ARCGIS tool. It comprises monthly climatological recordings (e.g., rainfall, temperature, wind speed), distributed land cover, soil map, groundwater depth, topography, and slope. The long-term temporal and spatial average monthly precipitation (58 mm) is distributed as 29% (17 mm) surface runoff, 27% (16 mm) actual evapotranspiration, and 44% (25 mm) groundwater recharge. The mean annual groundwater recharge, actual evapotranspiration, and surface runoff were 307, 190, and 199 mm, respectively. The findings of the WetSpass-M model are intended to support integrated groundwater modeling. The analysis of simulation results shows that WetSpass-M model works properly to simulate hydrological water budget components in the Drava basin. Moreover, a better understanding of the simulated long-term average spatial distribution about water balance components is useful for managing and planning the available water resources in the Drava basin.

Groundwater recharge estimation in karst aquifers of southern Apennines (Italy) by integration of remotely sensed data

In many Italian regions, karst aquifers are main sources of drinking water and play a crucial role for socio-economic development of the territory. Hence, estimating groundwater recharge of these aquifers is a fundamental task for a proper management of water resources, also considering impacts of climate changes.In karst areas of the southern Apennines, the assessment of hydrological parameters needed for the estimation of groundwater recharge is a challenging issue, specifically for the spatial discontinuity of the rain and air temperature monitoring networks and variability of land use. In such a framework, the integration of terrestrial and remotely sensed data is a promising approach to limit these uncertainties.This research deals with the estimation of groundwater recharge for karst aquifers of southern Apennines by the application of remotely sensed data gathered by the MODIS satellite in the period 2000-2014 for assessing actual evapotranspiration (MODIS Eta). To assess uncertainties in the estimation of Eta affecting conventional methods based on empirical formulas, MODIS Eta values were compared with those calculated by Turc, Coutagne and Thornthwaite methods. In addition, annual rainfall time series of 266 rain gauge and 150 air temperature stations, recorded by regional meteorological networks in the period 2000-2014, were considered to reconstruct regional distributed models of ETa and groundwater recharge.Considering the MODIS Eta, a mean annual groundwater recharge of about 448 mm∙year-1 was estimated for karst aquifers of southern Apennines. Instead, by the Turc, Coutagne and Thornthwaite formulas, ETa mean annual values of 494, 533 and 437 mm∙year-1 were estimated respectively.The obtained results open a new perspective in the assessment of actual evapotranspiration and groundwater recharge of karst aquifer at the regional and mean annual scales allowing a reduction of uncertainties and achieving a spatial resolution greater than that of the existing meteorological networks.

Chloride mass balance for estimation of groundwater recharge in a semi-arid catchment of northern Ethiopia

Limited scientific information has been published on the application of tools in the geographic information system (GIS) environment to understand factors that influence groundwater recharge. The objectives of the research reported here were to understand the spatial variability of factors that influence groundwater recharge using GIS, and to estimate the amount of groundwater recharge and its spatial distribution in Illala catchment, northern Ethiopia. Reconnaissance surveys coupled with satellite imagery were used to collect data related to water, dry-deposition and hydrogeology from the study catchment. The data analysis involved geo-statistics. The chloride mass balance (CMB) method was applied to estimate mean groundwater recharge. The study catchment is distinguished by a semi-arid climate (average aridity index value of 0.35) and it is dominated by limestone-shale-marl intercalation. Mean chloride concentration in rainwater ranges from 0.4 to 1.28 mg/L, while values in dry deposition vary from 1.78 to 1.82 mg/m2. Groundwater and runoff chloride concentration ranges are 1.4–31.96 mg/L and 0.60–1.56 mg/L, respectively. Mean annual groundwater recharge estimated by the CMB method varies from 6.1 to 288.3 mm, and the mean groundwater recharge represents 11.7% of the 548 mm mean annual rainfall. The CMB-derived groundwater recharge estimation showed a nearly comparable value with the recharge estimated by other approaches. More effort should be made to boost groundwater recharge using various recharge enhancing techniques such as constructing artificial recharge wells and water harvesting structures, targeting areas with the lowest recharge.

Spatial and temporal variability of groundwater recharge in Geba basin, Northern Ethiopia

WetSpa, a physically based, spatially distributed watershed model, has been used to study the spatial and temporal variation of recharge in the Geba basin, Northern Ethiopia. The model covers an area of about 4, 249 km2 and integrates elevation, soil and land-use data, hydrometeorological and river discharge data. The Geba basin has a highly variable topography ranging from 1000 to 3280 m with an average slope of 12.9%. The area is characterized by a distinct wet and long dry season with a mean annual precipitation of 681 mm and temperatures ranging between 6.5 °C and 32 °C. The model was simulated on daily basis for nearly four years (January 1, 2000 to December 18, 2003). It resulted in a good agreement between measured and simulated streamflow hydrographs with Nash-Sutcliffe efficiency of almost 70% and 85% for, respectively, the calibration and validation. The water balance terms show very strong spatial and temporal variability, about 3.8% of the total precipitation is intercepted by the plant canopy; 87.5% infiltrates into the soil (of which 13% percolates, 2.7% flows laterally off and 84.2% evapotranspired from the root zone), and 7.2% is surface runoff. The mean annual recharge varies from about 45 mm (2003) to 208 mm (2001), with average of 98.6 mm/yr. On monthly basis, August has the maximum (73 mm) and December the lowest (0.1 mm) recharge. The mean annual groundwater recharge spatially varies from 0 to 371 mm; mainly controlled by the distribution of rainfall amount, followed by soil and land-use, and to a certain extent, slope. About 21% of Geba has a recharge larger than 120 mm and 1% less than 5 mm.

A retrospective analysis of the climate change impact on the groundwater resources

Water balance and groundwater recharge simulations based on meteorological data with climate trends were made for the South-western part of Moscow artesian basin. Modeling results comparison of mean annual water balance and recharge values for previous (1965-1988) and present (1989-2012) periods allow to estimate their changes due to transient climate conditions. Assessment of groundwater resources climate changes was made on the basis of mean annual groundwater recharge maps for the investigated region for previous and present time periods, which showed their increase of 9% (720 thousands m3/d).