Jeff Masters says, in contemplating the recent flooding disasters:
An inordinate number of major U.S. floods this year
We’ve had an inordinate number of severe floods in the U.S. so far this year. The worst was the May Tennessee flood, which killed 31 people–the highest death toll from a non-tropical cyclone flooding event in the U.S. since 1994, and the most devastating disaster in Tennessee since the Civil War. The Tennessee floods were rated as a 1000-year flood for Middle Tennessee, West Tennessee, South Central and Western Kentucky and northern Mississippi.
We cannot say that any of this year’s flooding disasters were definitely due to global warming, and part of the reason for this year’s numerous U.S. flooding disasters is simply bad luck. However, higher temperatures do cause an increased chance of heavy precipitation events, and it is likely that the flooding in some of this year’s U.S. flooding disasters were significantly enhanced by the presence of more water vapor in the air due to global warming. We can expect a large increase in flooding disasters in the U.S. and worldwide if the climate continues to warm as expected.
I think Nielsen-Gammon was wrong in his analysis of the Nashville flood.