What would the Nashville, Tennessee flood of May, 2010 look like if it happened 100 years from now?

What is it about?

We know from previous studies that in a warming climate, there will be a shift towards more extreme rainfall events. Here, I wanted to take a present-day heavy rain event, and fast-forward 100 years to see how the storm would change in the future if a certain amount of warming were to occur. I selected a case that produced extreme flooding in the states of Kentucky and Tennessee, in the south-central USA. To test how the storm would have looked in the future, I first simulated the storm with a weather model using current conditions. The model simulation turned out pretty well. Then, I used an estimate of future warming, and applied this to the model input data, and re-ran the simulation with everything else set up the same. My initial idea was that winds in the lower atmosphere would intensify, and bring even more moisture into the system in a self-reinforcing way. However, this is not what the results showed. In the future, warmer simulation it did rain significantly more, with an increase in the maximum precipitation amount of 35-40%, which is remarkable given how much it rained in the present day event. But the cause of the increase was mostly just due to stronger updrafts in the thunderstorm cells themselves, rather than a systematically stronger transport by the winds over a larger area.

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Why is it important?

This study presented a method that can be used to assess how extreme weather events change as the climate changes. I have used a similar method to study several different weather phenomena. There are limits to the method, but it provides unique insights as to how extreme weather events will respond to different climates (it can be applied to warming or cooling scenarios). The models used to study large-scale climate change are too coarse to capture extreme weather like this, so this method provides a unique view. One of the many serious impacts of climate change is the potential for increased flooding. Here, we can get a glimpse of how peak rainfall rates, and storm-total precipitation in an extreme weather event would differ for a given amount of warming. This kind of information could be used to help cities prepare for future flooding events, for example by installing drainage systems with larger capacity, adding retention facilities, and increasing the amount of permeable surfaces in order to reduce runoff.

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