Comparing Flood Models From Federal Emergency Management Agency (FEMA), First Street Foundation's Flood Factor, and a Multi-Criteria Decision Analysis (MCDA) to Evaluate Flood Risk in the Rouge River Watershed

Abstract

Flooding in Southeastern Michigan is intensifying due to increasing temperatures, precipitation, and rapid urbanization. Such developments place an increasing number of people and capital at risk, which calls for public flood management as well as household level adaptation measures. Two models commonly used to understand flood risk and support flood management in the U.S. include: 1) Federal Emergency Management Agency (FEMA)'s flood zones and 2) First Street Foundation's Flood Factor model. FEMA's flood zones are mapped based on historical data, but they might not consider intense rainfall, a growing problem as the atmosphere warms. First Street Foundation's Flood Factor model integrates federal elevation, rainfall data and coastal flooding estimates from hurricanes, thus resulting in updated maps which show a vast increase in risk compared to official estimates. This study aims to compare the flood risk zones from FEMA's National Flood Hazard Layers and First Street Foundation's Flood Factor to analyze the percentage of properties at risk in the Rouge River Watershed of Southeast Michigan. Analyses identified almost a 2.5% and 5% increase in the number of parcels at risk in the 100-year and 500-year floodplain, respectively. This underestimated risk by FEMA represents almost 40% of the watershed population who might be unaware of the current and future flood risk. To further validate these additional at-risk parcels, a flood risk map of the watershed using a Multi-Criteria Decision Analysis (MCDA) model was created. This detailed comparative analysis involving two well-known flood models, along with this flood risk map, is a potential approach for improving flood management measures at a local or regional scale. This study can support climate adaptation by informing flood risk reduction solutions such as green infrastructure, preservation of open space and improved stormwater drainage systems.