According to the National Climate Assessment, the most extreme precipitation events (those in the 99th percentile of intensity) have increased in every region of the contiguous states since the 1950s. In the U.S., the highest precipitation events seem to be occurring more in the Northeast and across the Midwest. Image via National Climate Assessment
Depending on where you live, you could call 2014 the year of the drought, or the year of the deluge. In early August 2014, we have seen several significant rainfall events occur across the United States. During the week of August 10, for example, a slow moving area of low pressure across the Great Lakes and New England produced widespread showers and storms. Yesterday (August 19), parts of Phoenix (yes, the desert) recorded over four inches of rain in a short time period, thanks to an upper level low pushing into the western United States. Are extreme rainfall events related to climate change, and/or has urban sprawl contributed to flash flooding events due to more concrete and poor sewer systems? The answers to both questions are probably yes.
Is global warming responsible for the increase in urban flooding in the past few years? As we’ve all heard by now, computer models suggest that, as Earth’s climate warms, we are more than likely to see bigger swings in both rainfall events and droughts. Meanwhile, it’s super important to note that you cannot point to a single event and link it, clearly, to climate change or global warming.
However, after seeing repetitive episodes of extreme flooding – such as the floods in Nashville (2010) or Atlanta (2009) and such as the floods of August, 2014 – you might wonder when we will finally conclude that global warming is responsible. Some climate experts are now beginning to make this connection. According to Dr. Marshall Shepherd, Director of the Atmospheric Sciences Program at University of Georgia and host of WxGeeks on the Weather Channel, both humans and climate change do play a role in urban flooding. Shepherd says there is a unique formula that comes to mind regarding extreme rainfall events. That is:
Urban Flooding = Increase in intensity of top 1% rain events + expanding urban impervious land cover + storm water management engineered for rainstorms of “last century”
He explains how most of the flooding events that have occurred over the past 10 years are a result of “extreme meteorological conditions, urbanization, and people.”
One factor, he says, is the sheer size of cities, which are growing and becoming more spread out. As cities continue to expand in size, it’s as if a target has gotten larger and easier to hit. According to Shepherd:
If the bullseye is tripled in size, I probably have a better chance of hitting the bullseye more often. Warming climate is likely increasing the urban flood bullseye, making the probability of such flooding more likely.
Theresa Anderson, whose Ph.D. in Atmospheric Sciences at the University of Georgia came from research into hydrometeorology, says heavy rainfall and other extreme weather can severely impact big cities.
These heavy rain events are devastating for cities. Urban areas, which are expanding andaggregating, are not equipped to handle large volumes of water due to outdated storm water management, impervious surfaces, lack of vegetation, etc. Unfortunately, that leads to major flooding over a short period.
Dr. Marshall Shepherd
Hopefully these events are anomalies, but when considering the predictions of an accelerating water cycle, record rainfall events may be more likely.
Bottom line: Under conditions of a warming climate, a growing population and subsequent urban sprawl mean that extreme precipitation events are affecting cities more now than they did before 1970. Not one extreme weather event can be linked to global warming; however, computer models suggest that accelerating the water cycle via climate change will continue to bring about unusual precipitation events, including drought or flash flooding. Urban planners are beginning to speak of the need to adapt and improve cities’ infrastructures – for example, their drainage systems – to help reduce urban floods.
FULL STORY, PHOTOS, VIDEOS OF FLOODING AROUND THE U.S.: http://earthsky.org/earth/unusual-precipitation-patterns-in-the-u-s?utm_source=EarthSky+News&utm_campaign=65fa9730ca-EarthSky_News&utm_medium=email&utm_term=0_c643945d79-65fa9730ca-307928925
