Propagation from meteorological to hydrological drought and its application to drought prediction in the Xijiang River basin, South China

Exploring the propagation from meteorological drought to hydrological drought and its potential influence factors is crucial for early warning of hydrological drought. As a case study in the Xijiang River Basin (XRB), South China, the Standardized Precipitation Index (SPI) and Standardized Runoff Index (SRI) series from 1961 to 2013 were used to represent the meteorological drought and hydrological drought with daily runoff generated by VIC model. An identification process for the threshold and the mechanism of drought propagation was conducted based on rank order analysis and Copula theory. The drought propagation regulations of drought variables, geographical location, and lag-time were established by linear or non-linear functions. Eventually, the propagation regulations were applied to the hydrological drought prediction from 2021 to 2050. Results indicated that: (1) The spatial-temporal patterns of meteorological drought are the critical factors in triggering drought propagation, and the effects of meteorological drought area, drought severity, drought duration, drought spatial concentration, and drought persistent duration increase successively. The critical threshold for triggering drought propagation is the combined frequency of the above five drought variables greater than 0.14. (2) The geographic location, center number, duration, severity, and area of two drought types follow the linear, twopiecewise, power, linear and logarithmic functions, respectively. Drought mainly propagation from west to east in three-dimensional space, and the lag-time was less than three months, with the maximum being 78 days. Unlike triggering drought propagation, driving drought propagation is synthetically associated with meteorological, soil water, groundwater, and topography conditions. (3) Under the MRI-ESM2-0 model, the severity and area of hydrological drought under different scenarios in the 2021-2050 will increase compared with the reference period 1961-2013, and the extreme hydrological drought exceeding history may occur under scenarios SSP1-2.6, SSP2-4.5, and SSP5-8.5. The findings can help policy-makers manage the early stages of hydrological drought based on meteorological drought conditions and thus reduce the negative impact of drought hazards.