SWAT-based multi-index assessment of meteorological, agricultural, and hydrological drought characteristics in the Mekong River Basin

Abstract

Drought has intensified across the Mekong River Basin (MRB) due to climate variability and increasing human interventions, creating substantial risks for water resources and agriculture. This study applied the SWAT model to simulate hydrological processes and evaluate meteorological, agricultural, and hydrological droughts using the SPI, SSWI, and SRI indices. Model calibration (1982–2001) and validation (2002–2019) at seven hydrological stations produced satisfactory to very good performance, with R2 values ranging from 0.80 to 0.89 and 0.52 to 0.69, respectively. The model effectively captured seasonal flow dynamics, although uncertainties increased toward downstream regions influenced by reservoir operations and land-use change. Analysis of precipitation and soil moisture revealed strong spatial contrasts among sub-basins: upstream areas exhibited limited infiltration and rapid drainage. At the same time, midstream and downstream regions retained soil moisture longer due to favorable topography and soil characteristics. Multi-decadal drought evaluation reveals several prominent drought periods from 1970 to 2000, consistent with major large-scale climate anomalies. Correlation analysis shows stronger linkages among drought indices at longer accumulation periods, indicating tighter coupling of drought processes under prolonged dry conditions. Overall, integrating SWAT simulations with multi-index drought diagnostics provides a robust framework for characterizing meteorological, agricultural, and hydrological drought dynamics, supporting improved drought monitoring and water resource management in the MRB.