Wednesday, July 10, 2019

Bathtubs: Or When Words Fail

Frederick MD's Baker Park on Monday (source Frederick News Post)

Following a massive rain event that resulted in dramatic flooding along the I-270 Corridor between Frederick MD into Washington DC and suburban Virginia, I read a headline in the Washington Post that included the phrase “why the D.C. area was deluged by a month’s worth of rain in an hour.”  The article said:

The record-setting cloudburst unleashed four inches of water in a single hour, way too much for a paved-over, heavily populated urban area to cope with at the height of the morning rush.  The sheets of rain, with nowhere to run off, turned major roads into rivers while streams and creeks shot up 10 feet in less than an hour. The rushing water stranded scores of people in their vehicles, poured into businesses and the Metro system, submerged cars in parking lots, swamped basements and caused some roads to cave in, forming massive sinkholes.

Yes, it was a lot of rain that fell in a short period of time in an area marked by urban development (e.g., hard surfaces with limited drainage ability). But I kept reading for an answer to the question “Why?” Why the deluge? The article devolved into a discussion of warm air masses, stalled frontal boundaries and convective cells. But it still didn’t answer the question “Why?”

Then came the very last sentences in the article. Almost as an afterthought, a tepid explanation of the “why” behind the massive storm was tacked to the end of the piece by the author, simply:

Storm environments with these exceptionally high amounts of atmospheric water content are expected to increase from climate change-induced rising temperatures. And it’s plausible Monday’s rainstorm was intensified by the climate warming that has already occurred.

So much for a substantive explanation.

Fortunately, another article (a story published by WAMU, American University's radio station) in Washington, DC, did a much better job outlining both the evolution of the problem and the path going forward, as it is being laid out by FEMA and others.  The WAMU story correctly points out that:

This week’s flooding was caused by a short, intense storm that dumped water faster than stormwater pipes could carry it away. This is called interior flooding.  D.C. is also vulnerable to riverine flooding and tidal flooding. Both of these come from our rivers, but from different directions. Tidal flooding occurs when a coastal storm surge pushes up from the Chesapeake Bay, making the Potomac and Anacostia rise out of their banks. Riverine flooding occurs when a storm upstream brings too much water down the rivers.

More importantly, the article lays out the specifics of the climate problem and describes what city government is doing to address it and plan for the future.

Climate change is making all three types of flooding worse. Sea level is rising — already, the Potomac has risen 11 inches, and could go up another three feet. This makes tidal and riverine flooding more likely. At the same time, climate change is increasing the intensity of storms in the mid-Atlantic, meaning interior flooding is more likely, too. What was once considered a one-in-100-year storm could be a one-in-15-year storm by 2080….  Now, the District is spending $5 million to create a new, more accurate flood map that will take into account all three types of flooding as well as climate change, showing residents in much more accurate detail which areas are most ask risk.

“The modeling will tell us where to prioritize, and where the areas are more bathtub-like within the District,” says Tommy Wells, director of the District Department of Energy and Environment.  Wells says addressing those bathtub-like areas, where floodwaters can build up without draining, will be a major undertaking. It may require replacing some stormwater pipes with larger ones, and also rethinking other public areas that could hold water temporarily during an intense rainfall, keeping it from flooding homes and businesses.  “That next park that we build or redo or refurbish — maybe we need to drop that park down two or three feet so that water will be held there in the event of a major storm,” says Wells.


Update (a day later): A DC Area TV news story focused on the dramatic flooding in Frederick, MD's Baker Park (pictured at the top of this entry).  They said the massive deluge in the park was done on purpose.  It was the result of a deliberate flood mitigation system put in place to steer water away from populated areas!

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