Drought Characteristics Assessment of Main River Basins in Thailand Using Standardized Precipitation Index and Copula Function

Abstract

Over the past decade, drought has severely impacted Thailand's 22 major river basins, particularly affecting agricultural production and domestic water supply. These impacts result from climate change causing irregular and unseasonal rainfall patterns, making water management in river basins difficult and inefficient. This study analyzed temporal variations of the Standardized Precipitation Index (SPI) at 3-, 6-, 9-, and 12-month timescales for present and future conditions, using bias-corrected monthly rainfall data from climate models and employing run theory and copula functions to characterize drought. Results showed that under present conditions, mild droughts have return periods of approximately 13-15 years for SPI-3, increasing to 25-32 years for SPI-12. Severe droughts were found to be more frequent in northern river basins, including the Ping, Wang, Yom, and Nan River Basins, while less frequent in southeastern and central river basins. The findings can be applied to spatial water management planning by identifying risk areas and designing appropriate irrigation structures, developing time-specific early warning systems, supporting agricultural sector adaptation in high-risk areas, implementing climate change policies particularly in northern river basins prone to severe drought, and developing databases and information exchange systems among relevant agencies for efficient and sustainable water resource management.