GIS-based water balance modeling for estimating regional specific yield and distributed recharge in data-scarce hard-rock regions

• We estimate specific yield and recharge in hard-rock aquifers using DWTF technique.
• We examine spatial variations in specific yield, rainfall and recharge by GIS.
• Specific yield has greatest spatial variations in the area.
• Rainfall–recharge relationships are highly and moderately significant in 61% area.

In this study, a methodology is presented and demonstrated for combined estimation of regional specific yield and distributed recharge using double water-table fluctuation (DWTF) technique and geographical information system (GIS) in a hard-rock aquifer system of semi-arid regions. The study area was divided into 25 zones and groundwater budget components were computed for both wet and dry seasons using 11-year period (1996–2006) data. In each zone, the regional specific yield was estimated by applying the WTF technique for dry seasons and the rainfall recharge was estimated by applying the WTF technique for wet seasons. Zone-wise rainfall–recharge relationships were established using regression technique. Thereafter, the specific yield and recharge estimates were used with GIS to generate their maps. Surface-water bodies were found to significantly contribute to groundwater recharge. This finding underscores the need for adopting rainwater harvesting in the study area to enhance recharge. The regional specific yields were found to range from 0.038 to 0.002, whereas the mean rainfall recharge was found to vary from 0.5 to 10.9 cm. The box–whisker plots of z-scale transformed specific yield revealed the greatest spatial variation. The spatial and temporal variations of the rainfall recharge in the study area are statistically significant (p < 0.05 and CV > 30%). The developed rainfall–recharge relationships were found to be ‘highly significant’ (r2 ≥ 0.54, p < 0.05) in four zones, ‘moderately significant’ (0.54 > r2 ≥ 0.36, p < 0.01) in ten zones and ‘insignificant’ (r2 < 0.36) in the remaining zones.