Evaluation of the impact of anthropogenic storage on the hydrological drought propagation in two contrasting semi-arid river basins

This study quantitatively assessed the impacts of reservoirs on drought propagation in two semi-arid river basins: the Tapi basin with the Ukai reservoir in India (South Asia) and the Chirchik basin with the Charvak reservoir in Uzbekistan (Central Asia). Meteorological and hydrological droughts were characterized and analyzed using the Standardized Precipitation Index (SPI) and the Standardized Streamflow Index (SSI). Both river basins, especially in upstream reservoir areas, exhibited a notable correlation between hydrological drought (HD) and meteorological drought (MD). Reservoir operations resulted in lower MD-HD correlation in downstream areas for shorter SPI timescales, attributed to the influence of reservoir regulation. Hit score-based evaluations indicated reservoir operation-induced changes in drought propagation for both river basins. Due to the contrasting characteristics, the river basins showed a significant variation in the monthly lag time values, with distinct influences from monsoon (Tapi) and snow melting (Chirchik). In the Chirchik basin, the snowmelt season (April-September) had a shorter propagation time from MD to HD (average DPT: 5 months) and a longer time in the accumulation period (October-March; average DPT: 6 months). In the Tapi basin, influenced by the monsoon, the propagation time was shorter (June-September; average DPT: 4 months) and longer in the pre-monsoon period (average DPT: 6 months). both river basins.