[M-IS04] Extreme Weather and Water-Related Disasters in Asia

[MIS04-P07] Extreme Precipitation, Monsoon Influence, and Catastrophic Flooding in Northern Thailand: Insights from Synthetic Aperture Radar

★Invited Papers

*小山 朋子¹、李 在庸¹、渡部 浩平¹ (1.ICEYE)

キーワード：合成開口レーダー、台風、モンスーン、洪水

Chiang Rai Province, particularly Mae Sai District, experienced catastrophic flooding in 2024, with seven flooding events occurring by mid-September. This is significantly higher than the usual 2-3 incidents per year. This study investigates the critical role of extreme precipitation and the influence of the monsoon in driving the severe flooding in mid-September. Typhoon Yagi, which made landfall in Vietnam on September 7, 2024, weakened before reaching Thailand. However, its residual effects triggered heavy rainfall across the region, especially in Laos and subsequently at the headwaters of the Ruak and Sai Rivers in Myanmar. This situation coincided with a persistent monsoon trough across northern Thailand, resulting in a prolonged period of exceptionally high cumulative rainfall. A peak 24-hour rainfall of 235.8 mm was recorded in Mae Sai on September 11, exceeding the threshold for "very heavy rainfall." The resulting inundation was analyzed using various data sources, including synthetic aperture radar (SAR) imagery, which confirmed the extensive flooding. The cumulative rainfall since June had saturated the soil, reducing its water absorption capacity and further exacerbating the flooding.
Our team at ICEYE has been continuously monitoring flood extent and depth reports for significant flooding events utilizing imagery from the SAR satellite fleet and auxiliary data. We will present the findings on how extreme precipitation, amplified by the monsoon's influence, led to the catastrophic flooding in Northern Thailand.