Spatio-temporal Variability of Discharge Over the Past 40 Years in Krishna and Koyna Rivers, India

Long-term discharge variability assessment in the river channels helps to improve the water management strategies under the changing climate change scenarios. The present study investigated the 40-year (1970–2010) spatio-temporal variability in the discharge of the Krishna and Koyna River channels at Karad and Varunji gauging stations. Mean annual discharge (MAQ), mean decadal discharge (MDQ), standard deviation (SD), coefficient of variation (CV) and Pearson correlation coefficient (R), and variance (R2) were calculated from the daily discharge data to know the spatio-temporal variability. Possible causes of discharge variability were investigated from rainfall, topography, drainage, and reservoir data. Rainfall data (1998–2000) were collected from the Indian meteorological department and satellite-derived tropical rainfall measuring mission to examine the hydrologic response to discharge. Similarly, shuttle radar topography mission digital elevation model data were incorporated into ArcGIS software to generate relief, slope, drainage, reservoir, and basin data to quantify their relative influence with discharge. Results explored whether a significant variability existed in the 40-year historical discharge in the Krishna and Koyna River channels. Low MAQ for both the channels was recorded during 2000–2001, while it was maximum during 2006–2007. Krishna River’s MDQ was higher as compared to Koyna River. The highest SD value (2358.4 m3/s) was recorded for 2000–2010 and minimum (416.5 m3/s) for the 1970–1980 decade. The CV of the Varunji station was lower in 1970–1980 (0.2) while higher in 2000–2010 (0.7) with a rising trend from 1970–1980 to 2000–2010 decade. The Krishna and Koyna River flow regime has changed over the four decades due to variations in rainfall, relief, slope, drainage, reservoir, and basin area within both the basins. The results could be useful to the regional climate and flood forecasting centres not only in the Krishna and Koyna river basin, but also in other basins which have similar hydrogeological characteristics.