Scientists from the Tennessee Technological University and the University of Colorado, Boulder, explain why large dams bring more rain.
First, the reservoir behind the dam produces excessive evaporation that falls to the earth as rain. This seems obvious.
But what's more, says the Newsweek article that reported on the finding, "dams increase atmospheric instabilities in the vertical profile of temperature and humidity."
The increased instability "enhances the amount of convective energy in the air above the reservoir." That means more thunderstorms of greater intensity than before. That, in turn, means higher and more frequent floods than engineers had calculated when they built the dam.
And that, say the scientists, "...raises concerns about dam safety."