Understanding Flood Risks for Better Planning and Resilience: Novel Stochastic Models and Methods for South-East Asia

Abstract

Throughout history, human beings have been attracted to waterfront living. Today, most residents live in cities, most of which, in turn, are built on flood plains and in coastal areas – areas often threatened by floods. Physical changes to the environment have changed the response of catchments and rivers to heavy rainfall. Despite attempts to control the size of floods, economic growth – especially as experienced in Asia – has led to an explosion in exposure to floods. The most integrated, cost-effective method for disaster reduction and prevention requires that risk be assessed purposefully and adequately. Disaster risk is captured in two major components: occurrence probability and event intensity and reach, and its consequences. Understanding the risks associated with floods in Asia has been hindered by the complexity of flood dynamics in large river basins and in existing or unreliable datasets. With calculation power increasingly available, the development of flexible modeling systems and the appearance of new datasets, so-called probabilistic flood models can now be developed for large areas to quantify risks. A flexible modeling framework has been developed at DHI to better characterize flood plains and complex hydraulic systems in datapoor and highly exposed areas in Asia. The model relies on automated processes merging freely available datasets such as HydroSHEDS, WorldPop, crowd-sourced data available in OpenStreet Map and Landsat 7 and 8 satellite imagery. The combination of spatial data sources provides opportunities to optimize the hydrodynamic model domain and to improve the lowresolution digital elevation model. Such methods enhance flood hazard information conventionally derived from deterministic models by taking a full probabilistic approach considering source loading conditions, e.g., weather events and sea level rise, and the performance of existing and planned mitigation measures and failures of control structures such as dykes. With risks better quantified, new opportunities arise for cost-effective mitigation and resilience measures and for the development of novel risk transfer schemes through the use of insurance and capital markets.