Aquifers are important sources of water in arid areas, where no surface water exist. Estimation of groundwater recharge from rainfall is a big challenge for hydrogeologists, due to the high uncertainty involved. It is even harder to estimate recharge in arid areas, due to high variability of meteorological parameters in space and time. Unlike recharge in humid and sub-humid areas, recharge in arid areas occurs indirectly after rainfall-runoff accumulates in low lands such as land depressions and recharges the aquifer. A new method for recharge estimation in arid areas has proposed in this study based on soil-water budget model and utilizing geoprocessing tools in GIS. The method uses Digital Elevation Model (DEM), land-cover and rainfall distribution to estimate runoff accumulation in depressions. The soil-water budget model is then applied to estimate the groundwater recharge in areas of runoff accumulation. The geoprocessing tools in GIS such as flow direction and flow accumulation in Spatial Analyst were utilised. The application of the proposed methodology in GIS makes it easy to cover the entire area of study, and to run maps algebra. The method was applied to the entire area of Qatar. The proposed methodology was applied on Qatar as a case study. The spatial resolution of raster maps was 350 by 350 m and the temporal resolution is one day. Data requirements for this study include daily records of rainfall, Digital Elevation Model (DEM) for topography, soil-moisture holding capacity, land-use map and potential evapotranspiration. Recharge is calculated for each cell and summed to provide the total amount. The proposed methodology was applied on the entire country of Qatar using the hydrological year 2013-2014 and daily time steps. This year was selected because enough daily rainfall data was available for this period, with a good coverage of the entire country. Results obtained in this study for the hydrological year 2013/2014 show the total groundwater recharge is approximately 14 million m3, and concentrated more in the northern part of Qatar. The method can be applied on any arid region.


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