Propagation from Meteorological to Hydrological Drought and Its Influencing Factors in the Huaihe River Basin

Understanding the propagation from meteorological to hydrological drought is crucial for hydrological drought monitoring and forecasting. In this study, daily precipitation and streamflow data of 16 sub-catchments in the Huaihe River Basin from 1980 to 2014 are used to establish a framework to quantitatively reveal the propagation relationship between meteorological and hydrological drought and explore the impact of climate, catchment properties, and human activities on drought propagation. The propagation from meteorological to hydrological drought is divided into three types. Type-1 propagation indicates that one or several meteorological droughts trigger a hydrological drought. The occurrence probability of Type-1 calculated by the conditional probability on SPI and SRI series varies from 0.25 to 0.48 among all catchments. Features of Type-1 propagation can be concluded as lengthening of duration, amplification of severity, lag of onset time, and reduction of speed. Type-2 propagation indicates that a meteorological drought occurs but no hydrological drought occurs, which accounts for 63-77% of the total meteorological drought events in all catchments. Type-3 indicates that a hydrological drought occurs without a proceeding meteorological drought, which is caused mostly by human activities. The occurrence probability of Type-3 ranges from 0.31 to 0.58. Climate factors have significant effects on hydrological drought duration, while catchment properties represented by topographic index and base flow index significantly relate to hydrological drought severity, propagation time, and occurrence probability of Type-1 propagation. The ratio of crop land reflecting irrigation on hydrological drought is far less than that of topographic index, denoting that the impact of irrigation on hydrological drought is less than that of catchment properties. Reservoirs have significant effects on alleviating the duration and severity of extreme hydrological droughts, but little effects on the average duration and severity of hydrological droughts.