Splash! Photo by Charlotte Sutte (C’23).
By Charlotte Suttee
10.18 inches of rain fell onto Sewanee January 2020. That makes the start of 2020 one of the rainiest Januarys on record. In the last issue, data concluded that 2017, 2018, and 2019 were the rainiest years in Sewanee’s recorded weather history (with the exception of unprecedented levels in 1975). The trendline measures a 10 percent increase in average rainfall since 1899.
“This is a climate trend,” said Keri Watson, assistant professor specializing in Earth and Environmental systems. “In the Southeast, we are expecting increases in precipitation. Instead of small events, we are expecting that precipitation to come in fewer rain events.”
“Typically for us, more rain is better,” said Sewanee Farm Manager Carolyn Hoagland. “At some point there is an inflection point where more rain would not be helpful… When there’s more rain there are more clouds. You would have decreasing temperatures, less sunshine to make sugars, but so far, we haven’t seen that… When it’s really wet, we can’t even walk on the soggy soil [on the farm] or we will damage it.”
On the other hand, if plants are stressed for water, they have to use their photosynthesis-generated sugars to create molecules that help them withstand the stress instead of growing more shoots and leaves.
Hoagland emphasized the benefits of current rain trends for the Sewanee’s crops: “During rain, more minerals are in the solution— they are more likely to be in the soil solution and are available to the plants. There is also less heat stress during the day.”
However, the trend is not only more rain, but rain in harder and more scattered events. They are powerful enough to rapidly alter the geography of the plateau. “Rockfalls are often preceded by heavy rains,” said Geology Professor Bran Potter. “I wouldn’t be surprised to see more of that here.”
In 1994, 4,100 cubic meters of Warren Point Sandstone on the northeastern side of the plateau collapsed onto the Racoon Mountain formation below it. The most significant contributing causes of the rockfall: the undercutting of the bluff by weathering the siltstone and 45.59 inches of rainfall in the six months before the collapse.
“We can’t look at where it has flooded in the past and predict that’s where it will flood in the future because we have rapidly changing trends,” said Watson. “The last three years are indicative of that.”
Downtown Sewanee is developing and the plan of recent is to double impervious surfaces, which prevents water from entering the ground and presents a flood hazard.
“I have family in Baton Rouge and Houston, both of which have recently had huge flooding events, and one reason why those flood events were so damaging was because they were huge, but another reason is because they hit houses that were not in [legally designated] flood zones.”
While the climate and rain trends of Sewanee may be predictable, the effects of the weather are becoming less so. Domain Manager Nathan Wilson encourages students to take a look at the data and peer-reviewed research about local weather and global climate.