Trends in Extreme Streamflow Indices in the Godavari River Basin

This study assesses the spatio-temporal changes in trends in extreme streamflow indices for nineteen stream gauging stations in the Godavari River basin (area ≈ 312,812 km²), India. The daily streamflow data were quality checked and thereafter adopted to derive the magnitude (total annual runoff, annual maximum 1-day and 5-day streamflows) and threshold (total streamflow exceeding the threshold corresponding to 95th and 99th percentile discharge and mean annual flood discharge) based extreme streamflow indices for each station. The non-parametric Pettit's test is adopted for change point detection, while the Spearman's Rho and Modified Mann–Kendall tests are executed to detect the significance of trends in the extreme streamflow indices. Further, the changes in the distributional characteristics of mean and extreme flows are analyzed using a non-parametric kernel density estimate and Mann–Whitney test by dividing the entire duration into three sub-periods (i.e., before 1980, during 1981–1995, and after 1995). The results indicated declining trends in total annual runoff and extreme streamflows at most stations across the basin. The significant changes in the distributional characteristics of streamflows are observed in the sub-period after 1995 compared to the other sub-periods. The reported decrease in total runoff would put additional stress on the freshwater ecosystem services, which are already stressed due to human interventions.