The changing characteristics of propagation time from meteorological drought to hydrological drought in the Yangtze River basin, China

Understanding the drought propagation from meteorological drought (MD) to hydrological drought (HD) can help assist in the drought early warning and reduce drought related losses. Propagation time is a significant variable in describing drought propagation. In this study, we identify the MD and HD using the three-dimensional drought identification method to reflect the drought characteristics over temporally continuous periods and spatially adjacent areas. Then, we calculate the drought propagation time by considering the spatio-temporal overlaps between MD and HD events, which can provide further insight to reveal the drought propagation process in both time and space. Specifically, we consider the propagation time of interval of the start (Delta T-s), peak (Delta T-p), and end (Delta T-e) time between a paired MD event and HD event, respectively. The propagation process from MD to HD is investigated during 1961-2015 in the Yangtze River basin, China. Results indicate that the majority (>70%) of HD events are well matched with the majority (>70%) of MD events, and there are decomposed effect and joint effect during the propagation process from MD to HD. A stronger link between HD events and MD events with higher matching rate of MD and HD events is observed in autumn (SON) than the remaining three seasons. We find that the MD events in Yangtze River basin generally need 2 to 4 months to propagate to the HD events, and such response time from MD to HD events is becoming longer in most subbasins as the propagation time (Delta T-s,Delta T-p, and Delta T-e) show a significant increasing trend. The results in our study can help understand the drought development and the drought propagation, and are also helpful for water managers to make rational water resources management decisions.