Flooding assesses how the number of property-damaging floods has changed in Southeast Michigan in the most recent five years of data (2017–2021) compared to the previous 10 years (2007–2016). Human changes to the landscape in Southeast Michigan, such as removing forests and wetlands for development and agriculture and burying streams beneath pavement (i.e., “ghost streams”), means that more water runs off the landscape into rivers and streams during rains and snow melts. Combined with potential changes in rainfall patterns in recent years, these landscape changes could be increasing the amount of flooding in this region.
How is it scored?
This indicator was scored at the watershed scale using the average number of floods reported in the NOAA storm events database for the most recent five years of available data, 2017–2021. The threshold used for scoring was the average number of floods from 2007–2016 (average = 0.72). If the number of floods was less than the average, then the score was calculated as y = -69.4444x + 100, where x is the average number of recent floods in a watershed. If the number of floods was greater than the average, then a score was calculated as y = -64.103x + 96.154. Using this scoring method, a watershed would score a 50 if the number of floods in the most recent five years was equal to the average from 2007–2016.
We explored using river flood levels from USGS gages in the region, but found that the coverage was too limited and/or established flood height information was lacking for many gages.
Data source: National Oceanic and Atmospheric Administration’s storm events database (https://www.ncdc.noaa.gov/stormevents/).