On August 1 in Miami Beach, more than 6.5 inches of rain fell at City Hall within a three-hour period causing flooding in portions of the City.1 For the Miami Beach area, this type of event historically has a 2% chance of happening in any given year. You may also hear this referred to as a 50-year 3-hour storm.2
South Florida communities rely on gravity-based stormwater collection systems to carry runoff from its neighborhoods. The water eventually flows to the Everglades or the ocean, or it is allowed to seep through the soil to the water table below us. This means that our systems rely on water being able to flow freely from areas of higher elevations to lower elevations. Eventually, the water flows away from our urban communities. However, as sea levels rise, gravity-based systems become less effective as the difference between land and sea elevations reduce.
In Miami Beach, many of the challenges associated with rising seas and our changing landscape are being addressed by updates to the stormwater system, including new stormwater pumps. So far, 15% of the system has been installed, designed to handle rain falling at 3 inches per hour, and a total amount of 7.5 inches.
Yesterday’s extreme storm, however, was more intense with rain falling at more than 7 inches per hour during the peak of the storm.1 Considering the limited resources of local governments, it is far too expensive to build systems designed to immediately handle rainfall from the most extreme storms.
The pumps made a noticeable difference in reducing the severity and duration of flooding in the areas where they are currently in service. The City reported that most businesses in the vicinity of the pumps were operating within an hour after the storm, and the flooding receded much faster than in other parts of the City. In Miami Beach, the impacts of storms like the one on August 1 will be shorter and less severe as the new pump systems are built out, but they cannot be eliminated altogether.
Not the first extreme event this summer
Already this summer, there have been several other extreme rainfall events in Miami-Dade and Broward Counties. From June 6-8, the City of Weston experienced nearly 13 inches of rainfall over a three-day period,3 the equivalent of a 25-year storm which has a 4% chance of occurring in any given year.2 This was the storm that shut down the Sawgrass Mills Mall for three days, and by our calculations could have cost the State upwards of $1.3 million in sales tax revenue.4
We still have a lot to learn about how we can adapt to and mitigate the effects of sea level rise. It is becoming increasingly clear that even with strong government action, there is a need for individual actions as well. Miami Beach is at the beginning of its adaptation journey, and we all can learn from the experiences of a community leading the world in adapting to sea level rise.
At Brizaga, we are here to provide actionable information for individuals and businesses to make well-informed decisions in the face of the challenges associated with sea level rise. It is the missing puzzle piece in creating strong, resilient and vibrant communities for decades to come. Stay tuned for some exciting announcements in the coming weeks! Sign up for our mailing list to be the first to find out.
2. National Oceanographic and Atmospheric Administration (NOAA) Atlas 14 Point Precipitation Frequency Estimates
3. Community Collaborative Rain, Hail & Snow Network (CoCoRaHS)
4. Miami Herald (http://www.miamiherald.com/news/business/article155227249.html)