The influence of anthropogenic climate change on meteorological drought in the Lancang-Mekong River basin

Frequent occurrence of droughts in the Lancang-Mekong River Basin (LMRB) has produced incalculable impacts on human livelihood and river ecosystem. However, the roles of natural and anthropogenic forcings in the spatio-temporal evolution and characteristics of droughts have yet to be comprehensively explored, nor being well disentangled. In this study, two reanalysis climate datasets and an ensemble of 9 CMIP6 model simulations were used to investigate the influences of natural and anthropogenic external forcings on drought evolutions in LMRB during 1951–2020, using the standardized precipitation index (SPI) and standardized precipitation evapotranspiration index (SPEI). The changes in drought frequency, duration, severity, intensity, and affected area and their Copula-based multi-dimensional drought probabilities were also analyzed at both gridded and sub-regional scales. Results reveal: (1) for SPI, a robust forcing from greenhouse gases is substantially detected in observational signals during dry season, especially in spring; (2) for SPEI, the anthropogenic signal is strongly attributable, especially over longer temporal scales and larger geographical areas, while the natural forcing is only detectable in dry season with underestimated degrees of changes; (3) for univariate drought characteristics, the human activities have exacerbated drought conditions throughout LMRB, especially the drought frequency in the lower Lancang River basin, and drought duration and severity in the middle and lower Mekong River basin; (4) for multi-dimensional drought characteristics, anthropogenic activities have general decreased the co-occurrence probability of multi-dimensional droughts in the Lancang Rivier basin, but increased the risk of multi-dimensional drought events associated with long duration in the Mekong River basin. These findings could be beneficial to better understand the impacts of anthropogenic climate change on droughts and provide a timely evidence base for drought mitigation in the important trans-boundary regions of LMRB under a changing environment.