Dam operation affects the evolution and propagation of hydrological extremes

Dams are an integral component of water resources systems and management in the Upper Ganga basin. However, the impact of dam operations on the characteristics of hydrological extremes and their regional spatial pattern is less explored. Based on observational datasets, we studied the changes in the flood and drought characteristics at local and regional scales by comparing them during pre- and post-dam periods. It was observed that the annual frequency of streamflow is missing from the spectral representation of daily streamflow at the Tehri catchment during the post-dam period. The dam operation has reduced the flood peaks but increased their duration and volume, and the dam has influenced the variability in drought duration, intensity, and deficit. The operation of dams has changed the timing and strength of seasonality of these extremes. Ultimately, the dam has increased the risk of regional occurrences of droughts and minimized the risk of floods.