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Development of a Southwest monsoon index for monitoring rainfall in Thailand
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DOI：10.1016/j.pce.2026.104415.png)
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Abstract
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The Southwest Monsoon is a major driver of rainfall in Thailand and plays a critical role in water resources, agriculture, and disaster preparedness. However, increasing climate variability has made monsoon behaviour more irregular, resulting in unpredictable rainfall patterns and heightened risks of floods and droughts. This study develops a Southwest Monsoon Index (SWMI) based on the Sea Surface temperature (SST) contrast between two strategically selected regions of the Indian Ocean that influence moisture transport toward Thailand. Monthly satellite-derived SST imagery was processed using K-means colour segmentation to extract representative SST values from each region, and the resulting SST difference was used to construct the SWMI. Rainfall data from 1042 telemetry stations operated by the Hydro-Informatics Institute (HII) across Thailand were analysed to evaluate the relationship between the SWMI and monsoon-season rainfall. The results show a statistically significant negative correlation between the SWMI and accumulated rainfall (r =-0.74, p = 1.29 & times; 10-21), indicating that a stronger negative SST contrast is associated with increased monsoon rainfall. Spatial clustering of rainfall stations reveals that western and southern Thailand exhibit the strongest sensitivity to SWMI variations. This study demonstrates that the SWMI is a robust climatic indicator capable of capturing monsoon-driven rainfall variability in Thailand. The index provides a foundation for future seasonal and long-term rainfall forecasting, including integration with machine learning models. Its operational application has strong potential to support water-resource planning, agricultural management, and disaster risk reduction in Thailand.
Keywords:
Southwest monsoon index
Sea surface temperature
Rainfall in Thailand
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