Correlation between Tennant method and Standardized Precipitation Index for predicting environmental flow condition using rainfall in Godavari Basin

Abstract

Environmental flow is necessary to maintain a healthy ecosystem and sustain aquatic lives. Its assessment is thus aimed at analysing the minimum flow of water required for sustainability of the ecosystem. In the present study, an effort has been made to describe the environmental flow condition of a watershed with the help of a Standardized Precipitation Index (SPI), an index often used in drought prediction using precipitation. Among the various drought indices, SPI is very popular and widely used for drought monitoring. SPI is advantageous over other indices as, for example, it requires easily available precipitation data and enables drought monitoring at different timescales, such as monthly, seasonal, annual. On the other hand, the Tennant method requires flow data, which is too scarce in ungauged catchments. This study attempts to correlate the concepts of Tennant and SPI to explore the ability of SPI to predict environmental flow conditions using rainfall. The rainfall and runoff data for the period of 1990–2000 of five watersheds of Godavari Basin, namely Hivra, Kumhari, Nandgaon, Ramakona, and Satrapur, have been analysed. SPI at 9-month timescale for the month of June and the percentage of average annual flow for the same period were determined for respective watersheds separately. When plotted, both correlated positively with coefficient of determination of 0.74 for three (out of 5) catchments, suggesting a very good fit. The relationship indicates significant dependence of environmental flow on SPI, and it can be used for deriving the EF condition for a watershed/gauging site based on SPI, easily derivable from the available rainfall data.