Did Hurricane Joaquin Cause the South Carolina Flood of October 2015?

What is it about?

Record flooding took place across the state of South Carolina in early October, 2015, resulting in over $2B in damage and more than 25 fatalities. At the time of the flooding, Hurricane Joaquin was located offshore. Were these events connected? To answer this question, we used a computer model to simulate the flooding event as it happened (with Hurricane Joaquin), and then we ran experiments in which Joaquin was removed at the start of the model simulation. We that without Joaquin, very heavy rain still fell over the Southeastern US, but that the heaviest rainfall shifted northward into North Carolina. So we cannot conclude that Joaquin caused the flooding rains, but that it did influence their intensity and location by changing the upper-level flow pattern. Changes in the upper flow due to Joaquin played a larger role than supplying moisture, a role for Joaquin that had been previously speculated.

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Why is it important?

The flooding which took place over SC in early October, 2015, caused extreme societal impacts, and it is important to understand what causes such events. Specifically, given the nearby presence of Hurricane Joaquin during this event, we sought to understand any possible linkages between the flooding rains and the hurricane. If such flooding is directly associated with hurricanes, then predicting these events is closely tied to hurricane prediction. However, in this case, the events were somewhat independent, which means that accurate predictions of both the hurricane and the separate disturbance connected with the flooding are required.

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