Meteorological and hydrological droughts in the Lancang-Mekong River Basin: Spatiotemporal patterns and propagation

The Lancang-Mekong River Basin (LMRB) has been particularly vulnerable to serious and successive droughts during the last decades. Nevertheless, the characteristics of spatiotemporal variations in meteorological drought (MD) and hydrological drought (HD) with an emphasis on drought propagation have yet to be thoroughly investigated. In this study, based on reanalysis data, the standardized precipitation index (SPI) and standardized runoff index (SRI) were employed to comprehensively examine the evolution and propagation characteristics of MD and HD. Spearman rank correlation and wavelet analyses were employed for the correlation and propagation of MD to HD. The influencing factors of the drought propagation time (DPT) were also explored. The results indicate that: (1) During 1950-2021, the regions with worsening drought conditions were primarily in the Lancang River Basin in Yunnan Province, the highlands in north Laos, and the Khorat Plateau in Thailand. (2) The drought characteristics varied significantly on different timescales. For the longer timescales, the MDs and HDs corresponded to fewer drought events but longer durations and larger severities. The average duration and severity of HD were higher than MD on all selected timescales. (3) The DPTs from MD to HD exhibited noticeable spatial variability ranging from 2 to 9 months. In addition, there were statistically positive correlations between the MD and HD in each sub-region. (4) Precipitation was the dominant factor influencing the spatial distribution of DPTs at the basin scale, while the catchment properties, represented by the land use and elevation, had nonnegligible influences on the DPTs. (5) Human activities weakened the correlations between MD and HD. Meanwhile, the DPTs were prolonged as a result of human influence. Our findings highlight the characteristics of HD response to MD in the diverse sub-regions of the LMRB and provide crucial information for early warning and improvement of drought resilience in this transboundary international river.