Heavy rains were not the only cause of recent urban flooding, according to University of Georgia research meteorologist Marshall Shepherd. His June 2010 study also blames what he call ‘impervious cover’ – that is, roofs, streets, and sidewalks – for major flooding in Atlanta in 2009 and Nashville and Oklahoma City in 2010.
Marshall Shepherd: What we found with the Atlanta floods, and indeed many of the recent floods in 2010, is that it was a perfect convergence of several meteorological factors. But one of the other interesting aspects of this flooding event is the real signature of the impervious surfaces of the urban land cover.
Impervious surfaces, like roofs of buildings, sidewalks and parking lots, don’t absorb the rainwater the way soil does. The water runs off.
Marshall Shepherd: Coupled with streams and lakes that were already nearing capacity in terms of soil moisture, when you dump a lot of rainfall on urban impervious surfaces, it runs off in volumes quite rapidly. And it really had nowhere to go.
Dr. Shepherd said that humans are playing a bigger role than before in creating conditions that are ripe for floods in cities.
Marshall Shepherd: What we’re clearly seeing is that the role of human beings and their impervious surface is as much a part of the hydrological water cycle system in cities as the natural environment itself. These go hand in hand.
Dr. Marshall spoke more about the recent urban flooding.
Marshall Shepherd: The Atlanta floods of 2009 were really historic floods. We’re talking about 100 to 500 year flood events in many cases. And with the recent flooding in 2010 and places like Nashville and Oklahoma City, we were really interested in the context of that flood, it’s really historic nature and whether there are any possible implications as it relates to climate change and meteorological hazards in general.
Looking forward, Dr. Shepherd voiced concern over elevated risk to cities from flooding.
Marshall Shepherd: With each of the flooding events that we’ve seen recently in 2009 and 2010, there are certainly meteorological explanations. But what is important to note is that two things are happening. Urban impervious surfaces are increasing, which exacerbates these flooding events even more than they would have even a hundred years ago. And secondly, the Intergovernmental Panel on Climate Change has noted that the frequency and/or the intensity of extreme flooding events is expected to increase under a globally warmer climate. Now it’s certainly irresponsible at this point to suggest that these recent flooding events are directly linked to climate change, although these types of events are certainly consistent with what we would expect as our climate warms. So, really the message that we want to convey in this work is that the combination of increased impervious surfaces and the specter of increasing events like this under changing climate scenarios should certainly cause us to think about how we deal with these types of flooding events going forward.
Isn’t it kind of obvious, that pavement and roofs, etc. contribute ot such events?
Yet cities continue to cover every inch of blank area with houses and shopping areas.
Here in Oklahoma City, many wheatfields or other farmland/open areas are rapidly being converted to more lucrative housing and shopping districts. In the 20+ years we have lived here, we have seen many open areas get covered. the development we live in is only 25-30 years old. It would take a lot of rain to actually flood our development as seen on the South and North sides of town. We live on the West side of town, but are only about four miles west of the North Canadian River (now Oklahoma River in town). If it became worse than it has been, then it might happen. It would seem more likely to be hit by a tornado than flooded out where we live. (We have been missed by tornadoes as well, so far). Maybe it will take a University professor/scientist to wake up city planners, I don’t know.
With houses so close together (our house is less than ten feet from either neighbor’s house on each side and about 15 feet in front to the street, in back maybe 30 feet with both back yards), there is no place for absorption on any scale. In the development we lived in south of Winston-Salem, NC we had 1/2 acre plot with plenty of land to absorb the rains. In OKC with about 60×100 +/- no room. Some developemnts West of us have 5 acre plots, so it is not all small. Much of the city is small plots.
Speaking of the significant of roads……….
“We stand now where two roads diverge…… The road we have long been traveling is deceptively easy, a smooth superhighway on which we progress with great speed, but at its end lies disaster. The other fork of the road-the one “less traveled by”-offers our last, our only chance to reach a destination that assures the preservation of the earth.”
-Rachel Carson
Even though I am one who has come late to that fateful crossroads where two roads to the future diverge, perhaps it is not yet too late to make a difference that makes a difference by choosing the path to sustainability now.
-Steve Salmony
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