Standardized precipitation index-based approach to predict environmental flow condition

Environmental flow is one of the essential factors required to maintain the health of the river as well as the aquatic ecosystem. The present study describes the environmental flow conditions based on the percentage of average annual flow (%AAF) used in the Tennant method and the drought situations based on Standardized Precipitation Index (SPI) and investigates the existence of %AAF-SPI relationship. The study presents an attempt to correlate hydro-meteorology of the catchment with the eco-hydrology. High-flow season (July-September) rainfall and runoff data of 16 catchments from the Mahanadi, Godavari, Brahmani-Baitaini, and Tapi river basins were used for the independent derivation of both %AAF and SPI. The %AAF was plotted against the values of SPI (3-month scale) for the high-flow season for each of the study catchments. The R-2 values of greater than 0.63 for most of the catchments reveal the existence of robust relationship between the %AAF and SPI and enabled EF prediction for even ungauged catchments using SPI (rather than %AAF) derivable from easily available rainfall data only.