Assessment of Spatial and Temporal Variations in Runoff Potential under Changing Climatic Scenarios in Northern Part of Karnataka in India Using Geospatial Techniques

Abstract

The northern dry zone of Karnataka in Southern India is frequently affected by drought, and the overdraft of groundwater resulted in declining groundwater levels. In this context, spatial estimation of available runoff potential, planning and adoption of site-specific interventions for in-situ moisture conservation, supplementing irrigation and groundwater recharge are of prime concern. Therefore, spatial runoff estimation models were developed subdistrict-wise for the northern dry zone of Karnataka using the Soil Conservation Service Curve Number (SCS-CN) method and GIS. The estimated runoff was validated using the recorded data and was found satisfactory (R2 = 0.90). The results indicated that for major portion of the study area (61.8%), the mean annual rainfall varied spatially from 550 to 800 mm, and the runoff potential ranged from 10.0% to 20.0% of mean annual rainfall from 1951 to 2013. The higher rainfall and runoff potential was observed in the Khanapur subdistrict which lies in the western part of the selected area. It was observed that the number of subdistricts under the low-rainfall category (<550 mm) has increased, whereas the high-rainfall category (>1100 mm) has decreased over the years. Considerable variation in rainfall and runoff potential was observed during above normal, normal and drought years. The runoff generated from most of the study area was below 10.0% of mean annual rainfall in drought year, <30.0% in above normal year and <15.0% in normal year. The northern dry zone of Karnataka is vulnerable to drought and water scarcity, and the runoff potential was estimated under future scenarios using ENSEMBLE data of CMIP 5 to enable planners to design water-harvesting structures effectively. Finally, based on the modeling results, it was found that by 2050s (2040 to 2069), the runoff potential is expected to increase by 20.0% to 30.0% under RCP 8.5 and by 10.0% to 20.0% under RCP 4.5 and RCP 2.6 scenarios. By 2080s (2070–2099), the runoff is predicted to increase by >30.0% under RCP 8.5, by 20.0% to 30.0% under RCP 4.5 and by 10.0% to 20.0% under RCP 2.6, respectively. Even though considerable increase in runoff potential is predicted for the northern dry zone of Karnataka in the coming years, the current runoff potential itself is relatively high, and there is tremendous scope for its harvesting and utilization for in-situ moisture conservation, supplemental irrigation and groundwater recharge to ensure the long-term sustainability of the region