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Rainfall Estimates Are Outdated for Effective Stormwater Management Design

Whether it's pollinators, urban runoff, stream stabilization, or litter; within the field of conservation we all have different interests; and that's fine. Conservation topics are as diverse as the world we live in. However, the relentless cacophony of general news media paired with tailor made social media algorithms is likely resulting in important topics being overlooked by people who would otherwise be genuinely interested or concerned.

Enter my favorite type of blog post to write, an article review. It is my opportunity to rebroadcast a slice of my newsfeed to, hopefully, a different set of eyes.

Jim Morrison of the Washington Post recently published an article on April 9, 2021 with the headline "As rainstorms grow more severe and frequent, communities fail to prepare for the risks. "

The article introduced a new-to-me phrase "rain bombs." It's a very apt way to describe the intense, short duration, and perhaps unpredictable rain events which have become more common in recent years.

An eye-opening excerpt from the article states; "In 2019, researchers at the University of Wisconsin found that design guidelines based on Atlas 14 were dangerously inadequate. Looking at records from more than 900 weather stations from 1950 to 2017, they determined that 100-year storms — those with a 1 percent chance of occurring in a given year — were happening almost twice as often in the eastern half of the country as Atlas 14 predicted." Clearly things must change.

From my perspective, some of the obstacles to implementing accurate rainfall estimates in stormwater design are:

  • Higher initial cost to developers who would need to build bigger stormwater basins to handle the runoff.
  • Reluctance of cities to require more stringent standards for fear of losing development projects.
  • Lack of funds for interested cities to develop an accurate rainfall study.
  • State required design standards over-ruling local municipal desires.
  • Vacillating political trends related to climate science hamstring much needed on-going rainfall estimate studies.
  • Concern over real economic impacts related to building costs, property valuation, infrastructure costs (i.e. taxes), and much more. Stormwater truly effects everyone, whether they know it or not.

Thankfully, smart people are aware of this issue and working to correct it. In Ohio, the Construction General Permit (OHC000005) used current rainfall estimates during the renewal process in 2018. The result raised the standard for water quality treatment from the first 0.75 inches of rainfall to the first 0.90 inches of rainfall. The 0.90-inch number was however a compromise solution between what the data showed and feedback from the public comment period (i.e. lobbying groups). Additionally, the article mentions that there are bipartisan bills in Congress to provide funding to NOAA to keep the estimates updated.

I believe that we need to collectively, as a society, comes to grips with the fact that continuing our current path is unsustainable. Let us follow the data to determine the facts, create policy to address the problems, and allocate funds to implement solutions.

Blog author: Brent Eysenbach, Senior Program Manager - Stormwater & Technical Services

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