Understanding of Large-Scale Flood Processes With a Rainfall-Runoff-Inundation Model (PAP014385)

Código

PAP014385

Autores

Takahiro Sayama, Yuya Tatebe, Shigenobu Tanaka

Tema

Floods in a changing climate

Resumo

Understanding large-scale flood processes is essential for flood risk management in a changing climate. In 2011, the Chao Phraya River (CPR) basin in Thailand experienced large-scale flood resulted in the worst economic flood damage in the country. The flooding was induced mainly by unprecedented rainfall from five typhoons and tropical depressions between May and October. The total rainfall in the six months during the monsoon season was approximately 1,400 mm, while previous large-scale floods were caused by a total rainfall of approximately 1,200 mm and the average monsoon-season rainfall in this region is about 1,000 mm. The interpretation of the additional 200 mm of rainfall compared to past events can greatly affect the understanding of the 2011 flood disaster. Without understanding the impact of the rainfall variability on flood runoff and inundation, essential characteristics of the flood disaster may be misinterpreted. In this study, we conducted 52 year-long inundation simulation at the river basin scale. We applied a 2D Rainfall-Runoff-Inundation (RRI) model to the entire CPR basin. After the model validation with river discharges and water levels, remote sensing inundation extents, and peak inundation water depths for 2011, we conducted water balance analysis from the simulation results to investigate the relationship among rainfall, runoff and inundation volumes. The simulation, by taking two major dams into account, found that 131 mm (9%) of the total rainfall (P) 1,400 mm) may have flooded (F) at the peak. The slope of a linear regression between rainfall and flood inundation volume (dF/dP) was 0.25, suggesting that the additional 200 mm of rainfall may have resulted in a 50 mm, or 8.2 billion m3, increase in flood inundation volume. It accounts for more than 60 % of the total storage volume of the largest dam (Bhumibol dam: 13.5 billion m3). On the other hand, the contribution of the two major dams to reducing flood inundation volume was estimated to be 26 mm (4.4 billion m3) for the 2011 event. Hence, the extra 200 mm rainfall, or the additional 8.2 billion m3 of inundation volume, compared to the past large-scale floods, has great impact in the flood magnitude for the CPR basin. Furthermore, estimated elasticity (eF = (dF/F) / (dP/P)) of flood inundation volume to precipitation change is higher (eF ~ 2.9 to 4.2) than that of runoff volume (eR ~ 1.9 to 2.3), indicating that the flood inundation volume is more sensitive than runoff volume for the same change in rainfall amount. The analysis provides an important perspective in terms of climate change vulnerability to flooding. The presented dF/dP and dR/dP should be useful indicators for characterizing how climate change impacts on flooding in particular basins. Moreover, the presented rainfall-runoff-inundation simulation at a river basin scale should be an effective approach for the analysis of flooding including the assessment of climate change.