How much energy does it take to produce a torrential downpour?

Recently, the Duluth-Superior metro area had devastating flooding a result of rainfall totals of 10 inches or more in some locations. You may have seen photographs of the damage wrought by the flood waters — washed-out roads, flooded homes, ruined crops, etc.

Even in the face of such dramatic damage it is easy to overlook the enormous amount of energy that is involved in simply processing the water involved in such enormous amounts of precipitation.

Water is the only chemical in our atmosphere that can readily exist in all three of its phases — solid, liquid and gas. When 1 gram of water transitions from the high energy vapor phase (in which water is just another invisible gas) to the more familiar liquid phase (rain), 600 calories of energy are released to the atmosphere.

If 10 inches of rain were ever to fall over Dane County (with an area of 1,221 square miles), that would amount to 125 billion kilograms of water which, of course, would have originated from 125 billion kilograms of water vapor.

Since each gram of that huge amount of water vapor would have released 600 calories of energy to the atmosphere when it was condensed, a total of 75 quadrillion calories would have been released to the atmosphere to produce a 10-inch rainfall over Dane County. That is enough energy to power the Madison metro area for just a shade under 30 years. Clearly, a lot is going on energetically behind the scenes.

Category: Phenomena
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