Hydrological drought evolution and its response to meteorological drought in the middle-lower reach of the Yangtze River triggered by Three Gorges Reservoir

Based on monthly temperature and precipitation data from 183 meteorological stations in the Yangtze River ( YZR) Basin and monthly runoff data from three hydrological stations in the mainstream of the YZR during 1960-2016, this study, using the standardized precipitation evapotranspiration index ( SPEI) and standardized runoff index ( SRI), analyzed the multiple timescales evolution of hydrological drought and its response to meteorological drought at Yichang, Hankou, and Datong stations in the middle-lower reach of the YZR before and after the operation of the Three Gorges Reservoir (TGR). The results showed that with the operation of TGR, drought situations at the downstream hydrological stations in winter and spring were significantly reduced, while drought conditions were slightly aggravated in autumn. The occurrence frequency of moderate and severe drought at each hydrological station showed a declining trend in the post-TGR period, particularly for the moderate drought. The frequency of extreme drought demonstrated an increasing trend in general. With the TGR was impounded, the average drought duration of three hydrolog-ical stations showed relatively mild variations, whereas the average drought severity and peak exhibited a significant upward trend. Furthermore, the variation amplitude of drought characteristic variables at the short-term timescale ( 1 and 3 months) from three hydrological stations displayed an increasing trend along the middle-lower reach of the YZR, while decreasing trend happened at the long-term timescale (6 and 12 months). The correlation between SRI and SPEI series from three hydrological stations at short-term timescale decreased significantly, but the correlation increased rapidly with timescale increase. Correlation coefficient between the SRI and SPEI series reached the maximum at 12-month timescale and were slightly higher than that in the pre-TGR period. Meanwhile, the intra-annual correlation coefficients between the SRI and SPEI series at the short-term timescale declined evidently in the post-TGR period, particularly in winter. However, the correlation coefficients of the SRI and SPEI series at long-term timescale increased slightly. With the impacts of the TGR, average day number that hydrological drought lagged behind meteorological drought at Yichang station at different timescales increased or decreased, while the number of lagged days at Hankou and Datong stations increased significantly, and had an increasing trend along the middle-lower reach of the YZR. These results can provide reference for hydrological drought warning and optimal operation of reservoir under the changing environment. © 2022 by Journal of Lake Sciences.