Now, we’re told, we have a new reason to fear climate change: Record rainfalls are straining the capacity of combined-sewer overflow (CSO) systems in Richmond, Lynchburg and Alexandria. In heavy rains, the antiquated systems, which combine stormwater runoff and wastewater, release untreated wastewater into the river.
“We’re on the frontlines dealing with climate change,” Grace LeRose, program manager for the Richmond public utilities, told The Virginia Mercury. “We’re seeing bigger and more frequent storms that are going to tax our system even more.”
In May and June the city experienced 23 inches of rain, the highest ever recorded. That year, contends the Virginia Mercury, was indicative of a longer-term trend. There was a 33% increase in the number of heavy rainstorms in Virginia, and an 11% increase from the largest storms between 1948 and 2011.
Of course, you can make statistics say anything you want them to, so I thought I’d do some checking.
I consulted the weather.com rainfall database for Richmond. One set of tables displays a Top 10 list of monthly precipitation broken down by month. I arrayed the Top 10 months by year on a spreadsheet. You can see the results in the table above. It is readily apparent that years with months of heavy rainfall occur in clusters. There is a cluster around 1890, another in the mid-1930s, another in the late 1950s, another in the late 1970s, another in the early 2000s, and another in the last few years.
These heavy rainfall clusters do appear to be increasing in frequency, which is consistent with the idea that heavy rainfall events are increasing in intensity — although it’s also consistent with the idea that we’re just having more rainy days as opposed to more heavy rains.
It is also worth noting that the Top 10 month for rainfall in Richmond for all recorded time occurred in July 1945. That month saw 18.87 inches of rain. The next wettest month, Sept. 1999, experienced 16.6 inches, followed by Aug. 2004 with 16.3 inches.
May and June 2018 set a two-month record of 23.67 inches, as the Virginia Mercury points out. But June 2018 had only 13.32 inches.
If you’re cherry picking multiple-month periods for comparison, 1889 saw a four-month wet period with 39.96 inches of precipitation. That was 130 years ago in the pre-Global Warming days.
I also wonder why 1948 was selected as a base year. That year didn’t see a single Top 10 rainfall month. Would Virginia have seen a 33% increase in the number of heavy rainstorms if the base-line had been 1938 or 1958? Is there something magical about looking back 70 years, as opposed to any other number of years?
The question of how best to measure trends in the intensity of rainfall is not one easily resolved. But I don’t know that it matters. The fact is, Richmond, Lynchburg and Alexandria need to overhaul their ancient stormwater/sewer systems today, regardless of how precipitation has increased over the past century or how much it will continue to increase over the next century. CSOs have been prone to overflowing since they were built, and that reality hasn’t changed.
Perhaps a more useful question is to ask how Virginia’s older cities can cope with extreme weather events. Is it a better investment of scarce resources to build water treatment facilities with bigger capacity or to “soften” the city’s infrastructure of roofs, sidewalks, roads and streets to make them capable of filtering, storing, and slowing the release of rainwater? Richmond went through a flurry of building “rain gardens” a few years back. The rain gardens were looking pretty forlorn and neglected the last time I looked.
It’s probably easier (if not more cost effective) just to apply for state and federal grants, issue some bonds, and engineer a massive hard infrastructure project. That’s what Richmond is doing. The city is in the process of upgrading its wastewater plant, adding 65 million gallons per day over its existing 75 million gallons per day. I hope it’s worth the investment.
Leave a Reply
You must be logged in to post a comment.