Flood risk in past and future: A case study for the Pawtuxet River's record‐breaking March 2010 flood event

In this study, a detailed assessment of several factors that can influence the flood risk is presented. This case study in the Pawtuxet Watershed, United States, resulted in the following conclusions that are important to consider in flood risk management policies and strategies, and are ignored in existing tools and databases such as FEMA FIRMs.

For this case study, it was shown that small diversion dams (e.g., historical textile mill dams) have more impact on the risk of more frequent floods while their impact on very extreme events is not that significant. It was also shown that debris can highly increase the flood risk and consequently flood risk zones. Therefore, it is recommended to generate flood risk maps for similar regions for both scenarios (with and without debris). Otherwise, flood risk may be highly underestimated.

It was demonstrated that changes in extreme precipitation, and consequently in flood flow discharges, resulted in large uncertainty in the prediction of the 100‐year flood event and consequently flood zones in this area. In addition, wet hurricanes can potentially pose a high risk of inland flooding. In particular, it was demonstrated that a synthetic hurricane with two landfalls (Hurricane Rhody) can generate a record‐breaking rainfall, while the first landfall of this hurricane did not lead to significant flood risk.

The study concludes that extreme flooding has a trend, and historical data do not represent future flood risk. Therefore, at least, uncertainty should be included in flood maps that are generated based on the historical data. This uncertainty can be quantified based on the trend in the historical data as well as climate model predictions.