Water, water everywhere--Is climate change to blame?

It’s no secret that this has been a wet year. In fact, after record January and July rainfalls, the U.S. Forest Service’s Coweeta Hydrologic Lab is approaching its annual average already, at the end of July! Is all of this rain evidence of climate change?

Scientists emphasize that no single storm or flood can be attributed to climate change. After all, big storms and floods are part of the climate history of this region. But we can examine historical records for gradual changes in rainfall, and we can look at future projections to see what types of weather may be more likely in the future.

Marshall Shepherd, a University of Georgia professor, president of the American Meteorological Society, and researcher with the Coweeta Long Term Ecological Research (LTER) Program, provided a useful analogy: “No single home run in baseball can be attributed to steroid use, but steroid use likely increased the length and number of home runs during the ‘steroid era’ of the past two decades.” Do we see similar changes when we look at the big picture of climate in the region?

The U.S. Forest Service has collected nearly 80 years of weather data at the Coweeta Hydrologic Lab. While the USFS does not attempt to predict future climate, their data provide a window into history. A comprehensive study of Coweeta weather records from the 1930s to the 1980s found few climate trends, but an analysis of the last 30 years shows a different rainfall trend: dry years have become even drier, and wet years have become wetter.

These recent historical patterns are consistent with climate change predictions and with the findings of Shepherd and his colleagues at the University of Georgia. It’s important to understand the particular way that climate is affecting Southern Appalachia: the most important changes likely have to do not with average annual rainfall, but rather with the variability in precipitation. This is why it is not surprising to have so much rain right on the heels of last year’s drought, or to find that Coweeta’s wettest year on record (2009) came just two years after the driest.

Shepherd’s research shows that both droughts and flood-producing storms have become more frequent and extreme in Southern Appalachia, and as the climate changes we can expect even more droughts and floods.

Farmers already understand that yearly averages don’t tell the whole story. The timing of wet and dry spells and the intensity of rain are often more important. USFS data show that, over the last 30 years, summer months have been drier than historical averages while fall months have become wetter. During most autumn months, the increase was simply because it rained more often, but in September we have seen an increase in high-intensity, short-duration storms, including those linked to tropical storms. These are precisely the types of storms that are most likely to trigger landslides and flash floods.

So... is all of this water a result of climate change? Let’s just say that extremely wet years are consistent with a decades-long trend of increasing rainfall extremes and with the best predictions that we can make about the future.

If we continue to experience wetter wet years and more major storms, we are likely to see more flooding and landslides as well. With that in mind, we at the Coweeta LTER are currently proposing to study the potential risks and impacts of extremely heavy rains. The goal is to understand and map vulnerability to heavy rains, thereby helping people stay out of harm’s way and informing policy decisions.


This column is produced by members of the Coweeta Listening Project (CLP), a branch of the Coweeta Long Term Ecological Research Program. Views expressed here are not representative of the USDA Forest Service or the Coweeta Hydrologic Lab. Please share questions, comments, or suggestions for future topics at cwtlistn@uga.edu or Coweeta Listening Project, UGA, 210 Field St., Room 204, Athens, Georgia 30602.


Original Citation: The Coweeta Listening Project. Franklin Press. Column on "Science, Public Policy, Community." Page B4. August 2, 2013.