Assessing flood risk at the global scale: model setup, results, and sensitivity

Globally, economic losses from flooding exceeded $19 billion in 2012, and are rising rapidly. Hence,
there is an increasing need for global-scale flood risk assessments, also within the context of integrated
global assessments. We have developed and validated a model cascade for producing global flood risk
maps, based on numerous flood return-periods. Validation results indicate that the model simulates
interannual fluctuations in flood impacts well. The cascade involves: hydrological and hydraulic
modelling; extreme value statistics; inundation modelling; flood impact modelling; and estimating
annual expected impacts. The initial results estimate global impacts for several indicators, for example
annual expected exposed population (169 million); and annual expected exposed GDP ($1383 billion).
These results are relatively insensitive to the extreme value distribution employed to estimate low
frequency flood volumes. However, they are extremely sensitive to the assumed flood protection
standard; developing a database of such standards should be a research priority. Also, results are sensitive
to the use of two different climate forcing datasets. The impact model can easily accommodate new,
user-defined, impact indicators. We envisage several applications, for example: identifying risk hotspots;
calculating macro-scale risk for the insurance industry and large companies; and assessing potential
benefits (and costs) of adaptation measures.