Spatiotemporal patterns and propagation of meteorological and hydrological drought in a humid basin of Southeast China.

Droughts have caused great damage due to climate change and intensified human activities. Quantifying the propagation law of meteorological drought (MD) to hydrological drought (HD) is essential for drought warning, defense and adaption. In this study, based on the standardized precipitation evapotranspiration index (SPEI) and standardized runoff index (SRI), we analyzed the spatiotemporal characteristics and propagation patterns of MD and HD 1975-2020 in Minjiang River Basin (MRB) located in Southeast China. Furthermore, the effects of climate change and large reservoirs on the spread of drought were discussed. The results indicated that MRB experienced relatively severe MD and HD after 2000. All subbasins experienced MD and HD in spring, while they exhibit a trend of hydrological humidification in winter. The drought propagation time (DPT) from MD to HD generally 3 months. And spring and summer generally have a shorter DPT (2 months) than autumn and winter (3-5 months). Precipitation is the key meteorological factor affecting drought conditions in all four seasons, contributing over 80% to MD and HD, while the total impact of temperature and actual evapotranspiration (ETa) is less than 20%. ENSO is the most influential circulation factor affecting the drought variability of MRB, contributing over 50% to MD and HD, and followed by PDO. Reservoir discharge is the key factor leading to the trend of hydrological humidification in autumn and winter. The operations of large reservoirs since 1996 have extended the DPT by 4, 2, 3, and 5 months in spring, summer, autumn, and winter, respectively.