Watching the snow melt predicts flooding and drought

In 1997 floods attributed to melting snow in the Dakotas and Minnesota caused damage costing upwards of $3 billion dollars. Between December '96 and January '97 melting snow, in addition to torrential rain, caused $2-$3 billion in damages in California, Washington, Idaho, Nevada, and Montana.

To help mitigate such disasters, the Airborne Snow Survey monitors the snow on the ground in 25 states and 7 Canadian provinces during the winter and early spring, and it checks more than just how deep the snow is.

"The real question of interest is the amount of snow water equivalent on the ground. That is, the amount of water in the snow pack when it melts," says Tom Carroll, who works on the Airborne Snow Survey program.

In the summer, the Airborne Snow Survey planes fly over designated flight lines, and take a reading of background radiation coming from the Earth. This is the amount of electromagnetic radiation that is always being emitted from elements in the soil. Then, in the winter, the planes fly over the flight lines again, and take another radiation reading. This reading will be different from the first, depending on how much water (in the form of snow) is covering the ground. When the summer and winter measurements are compared, researchers can determine the snow water equivalent.

The information is used by National River Forecast Centers to predict likely areas of snowmelt flooding, or drought. If the snow water equivalent is high, the forecast centers can issue flood watches and warnings for the rivers in question. "The good news about snowmelt flooding," says hydrometeorologist Frank Richards, is that "it tends to be kind of a slow motion event. You see it coming and you can warn people to get out of the way."

In the same way, Richards says farmers can be warned about droughts and plant drought resistant crops. "In terms of water management, a mistake could be a billion dollar mistake in terms of mis-estimating the amount of snow."