Articles · Open Access Policy
Abstract
Freshwater resources support drinking water provision, irrigation, riverine ecosystems, and livelihoods, but are becoming increasingly influenced by irregular rainfall and increasing air temperatures. The current study was an assessment of the impact of climate variability on the hydrological response and availability of freshwater in the upper Cauvery River basin in Southern India for the period 1991–2020. These were combined in a semi-distributed hydrological model that was calibrated using daily gridded rainfall and observed streamflow data from 1995 to 2008 and validated using the observed streamflow data from 2009 to 2020. The climate variability characterization was conducted using annual anomalies, seasonal distribution, and long-term trends, and the freshwater availability characterization was done using flow duration characteristics and seasonal water yield. Monthly streamflow was well reproduced by the model, with efficiency values of 0.86 in calibration and 0.78 in validation. There was a slight rise in the mean annual temperature of approximately 0.27 °C per decade, and a slight decrease in the mean annual rainfall (8.1%) over the period 1991-2005 to 2006-2020. The mean annual runoff went down 20.7% over the same period, suggesting that streamflow reacted two and a half times more to rainfall. The mean annual water yield decreased from 9.40 to 7.47 billion m³, while the median monthly flow decreased approximately by one-third. The southwest monsoon produced almost three-fourths of the annual yield, while dry-season flows were very low and becoming more marginal. The results suggest that new hydrological baselines, seasonal storage management, and protected minimum flows and demand management in deficit years should be incorporated into water-allocation planning.