Multiple drought indices and their teleconnections with ENSO in various spatiotemporal scales over the Mekong River Basin

Drought may lead to severe and diverse impacts on agriculture, economy, and society across different regions and periods, posing predictive and adaptive challenges. In recent years, severe droughts have affected >60 million people in the Mekong River Basin (MRB). Additionally, El Niño Southern Oscillation (ENSO) episodes had distinct influences on the occurrence and intensity of drought variability in the regions. Understanding the spatiotemporal characteristics of droughts across the MRB is critical to improving management and mitigation actions. This study aims to investigate spatiotemporal drought characteristics in the MRB and their teleconnection with the ENSO. Three multiple drought indices, including the Standardized Precipitation Index (SPI) for meteorological drought, Standardized Soil Water Index (SSWI) for agricultural drought, and Standardized Runoff Index (SRI) for hydrological drought were calculated to quantify drought events, drought frequency, and drought severity. The overall patterns showed more events and larger intensity were identified by the SPI than those by the SRI or the SSWI, while the higher frequency was observed by the SRI. The Middle Mekong basins seem to experience more drought events, while higher levels of frequency and intensity of droughts were observed in the Upper Mekong Basin. The correlation analysis between ENSO index and precipitation suggested that the strongest ENSO events in Dec-Jan-Feb may result in developments of meteorological drought in Mar-Apr-May, and further led to hydrological and agricultural drought in Apr-May-Jun. Such ENSO effects had significant influences on drought variabilities in southern MRB and were insignificant in the north. The multiple drought indices show skills in identifying spatial and temporal drought characteristics from meteorological, agricultural, and hydrological perspectives, and potential for drought outlook further considering their ENSO teleconnections. The results can be applied to the development of drought monitoring methods and adaptive strategies to mitigate drought impacts through scientific and quantitative assessments.