Abstract
Abstract. The Thailand floods in 2011 caused unprecedented economic damage in the Chao Phraya River basin. To diagnose the flood hazard characteristics, this study analyses the hydrologic sensitivity of flood runoff and inundation to rainfall. The motivation is to address why the seemingly insignificant monsoon rainfall, or 1.2 times more rainfall than for past large floods, including the ones in 1995 and 2006, resulted in such devastating flooding. To quantify the hydrologic sensitivity, this study simulated long-term rainfall–runoff and inundation for the entire river basin (160 000 km2). The simulation suggested that the flood inundation volume was 1.6 times more in 2011 than for the past flood events. Furthermore, the elasticity index suggested that a 1 % increase in rainfall causes a 2.3 % increase in runoff and a 4.2 % increase in flood inundation. This study highlights the importance of sensitivity quantification for a better understanding of flood hazard characteristics; the presented basin-wide rainfall–runoff–inundation simulation was an effective approach to analyse the sensitivity of flood runoff and inundation at the river basin scale.
Highlights
The 2011 large-scale floods over the Chao Phraya River basin resulted in the worst ever economic flood damage to Thailand (The World Bank, 2012)
This study estimated the elasticity of flood runoff and inundation in the Chao Phraya River basin
Due to the flat topography with comparatively small bankfull river drainage, the delta suffers from frequent flood inundations
Summary
The 2011 large-scale floods over the Chao Phraya River basin resulted in the worst ever economic flood damage to Thailand (The World Bank, 2012). They concluded that the 2011 monsoon rainfall was not very unusual from a viewpoint of large-scale meteorology Instead they stressed that the main causes of the unprecedented flood damage lay in non-meteorological factors, including reservoir management and conversion of agricultural land into industrial complexes. Komori et al (2012) highlighted the fact that the seemingly insignificant rainfall may contribute significantly to the increase in runoff volume in the Chao Phraya River basin. They conceptually explained that the 1.4 times more rainfall than normal years might result in 2.5 times more runoff than normal years under a constant evapotranspiration assumption. They conceptually explained that the 1.4 times more rainfall than normal years might result in 2.5 times more runoff than normal years under a constant evapotranspiration assumption. Kotsuki and Tanaka (2013) performed a hydrologic simulation with a land surface model and concluded that runoff is highly sensitive to rainfall (2.25 times more than average) in a naturalized condition excluding dam effects
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