Relating trends in streamflow to anthropogenic influences: a case study of Himayat Sagar catchment, India

Abstract. Catchment development has been identified as potentially causing major changes in streamflow in India. This paper tests for trends in rainfall and streamflow in Himayat Sagar catchment and shows major declines in streamflow without significant changes in precipitation. It then relates the streamflow trends to anthropogenic influences in Himayat Sagar catchment. A simple rainfall-runoff regression model was used to quantify the change in magnitude of rainfall-runoff relationship over the study period. Then, the anthropogenic changes in the catchment including land use, watershed development, groundwater abstractions and storages, and evapotranspiration were quantified. The changes in the components of the water balance were then compared. Streamflows were found to decline at a rate of 3.6 mm yr⁻¹. The main land use change was found to be a conversion from rainfed to irrigated agriculture, fed by groundwater extractions. Irrigated area increased from 8% to 23% of the cropping area during the monsoon (Kharif) season (June–November) and from 8% to 16% of cropping area during the dry (Rabi) season (December–March). Various estimates of changes in evapotranspiration/irrigation water use were made. Well inventories suggest groundwater extractions increase of 7.2 mm yr⁻¹, typical irrigation practices suggests applied water increased by 10.8 mm yr⁻¹, while estimates of evapotranspirations using AVHRR images showed an increasing rate of 4.1 mm yr⁻¹. Surface water storage capacity for various small watershed development structures increased 2 mm over 7 yr. Taken together, the streamflow trends and groundwater information suggest the most plausible estimates of evapotranspiration changes comes from the AVHRR imagery.