The National Climate Assessment shows the Midwestern United States has already experienced large changes in very heavy precipitation and projects such changes to continue and worsen. The Minnehaha Creek Watershed District, responsible for Minneapolis, Minnesota and many of its western suburbs, wanted to better understand the climate threat to its stormwater management capabilities. The District considered climate projections to assess stormwater system vulnerability and adaptation options for two specific locations. The analysis used downscaled global climate model projections to identify the expected mid-century 1-10 year storm. Stormwater system resilience was then considered under these conditions and a number of areas were identified as undersized. For these areas, estimated costs and feasibility comparisons of several stormwater management adaptation strategies were considered against a baseline of expected flooding damages caused by no-action.
The relevance and need to anticipate and plan for future storm events was observed mere months after completion of the study when over 24 inches of rain fell in the Minneapolis area over a period of three months. This heavy precipitation led to historic water levels and flooding. Using this study to identify and prioritize undersized portions of the stormwater management system will help the Watershed District’s communities adapt to climate change. Recognizing the importance of its effort, the Watershed District developed a guidebook and held multiple outreach events to help other nearby communities replicate its approach and adapt to climate change.
(For more information about this case, view the U.S. Climate Resiliency Toolkit’s case study on the Minnehaha, MN Creek Watershed District Assesses Stormwater Management Climate Vulnerability.)