"We now have a model tool that can relatively rapidly assess flood risk in a consistent way around the world, under both current and future climate and socioeconomic conditions," Philip Ward of VU University Amsterdam told environmentalresearchweb. "This will provide valuable information to stakeholders such as international financing institutes, the (re-)insurance industry, multinational companies and intra-national institutes in their disaster risk reduction activities."

Developed with colleagues from VU University Amsterdam, Deltares, PBL Netherlands Environmental Assessment Agency and Utrecht University, Ward’s method uses a cascade of models, including the global hydrological model PCR-GLOBWB, inundation modelling, and a flood impact module that looks at affected population, GDP, agricultural value, economic urban asset exposure and urban damage. The team estimated risk based on a large number of different-sized flood events (with different probabilities), instead of just one or two.

"We decided to pursue this approach in response to an increased demand from diverse stakeholders for natural disaster risk assessments at the global scale," said Ward. "International financing institutes need strategic assessments of flood risk for developing risk profiles and deciding where to invest in risk reduction activities; the (re-)insurance industry requires global scale assessments to assess their current and future risk portfolios; multinational companies are interested in identifying possible risks in their supply chains; and intra-national institutes can use the data for monitoring progress in risk reduction activities, such as those related to the implementation of the Hyogo Framework for Action."

According to Ward, as with other past estimates of flood risk at the global scale, the team’s results represent overestimates of the actual flood risk. "This is because in the current version of the model we assume that no human-made flood protection measures are in place," he said. "In reality many regions are protected by infrastructural measures up to a certain design standard."

In the first assessment of its kind, the researchers found that the estimate of flood risk is highly sensitive to different flood protection standards. Assuming that all parts of the world are protected against floods with a 5-year return period, for example, reduces the overall risk by around 41–50%. Protection of all areas against floods with a 100-year return period, meanwhile, would cut the overall risk by 95–97%.

Ward believes that the development of a global database of flood protection standards should be a research priority. This would enable protection standards to be included in the model cascade, improving the accuracy of the flood risk results.

"We will be working towards using the model in an operational sense: there has already been a lot of demand for this," said Ward. "For example, we have already carried out a study of flood risk at the national scale in Nigeria for the World Bank, using the global flood risk models, and plan to carry out similar studies for the World Bank in the near future. Also, the model has now been implemented in the IMAGE integrated assessment model, which will allow policy makers to assess the change in risk under future scenarios of climate and socioeconomic change."

The team reported the results in Environmental Research Letters (ERL).

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