Friday, February 8, 2013

Snow monitoring methods reduce flood risk

Julie Hunt in  Thanks to new monitoring techniques that improve flood forecasting, Switzerland is now less prone to the catastrophic type of flooding that has hit the country over the past few decades. “We can now compare the current situation with other situations in previous years, and tell the flood forecasters if there is significantly more snow than average in the mountains that is due to melt over the next couple of days,” says researcher Tobias Jonas.

Jonas is a hydrologist at the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), a Davos-based institute carrying out cutting-edge work in the field.

The research is important as half of Switzerland is over 1,000 metres above sea level and a quarter over 2,000 metres, so roughly a third of all annual precipitation is snow. When it melts, it can lead to spring floods. In May 1999, heavy rainfall coincided with the main snowmelt period, resulting in devastating floods causing damage totalling SFr580 million ($626 million).

The disaster raised awareness of snow hydrology in general and led to the monitoring of snow water resources being integrated into the federal flood forecasting system. Keeping track of the distribution of snow is vital for predicting run off - the water that flows over the land when the soil is saturated and excess water from rain, melt water or other sources cannot be absorbed.

Water produced by melting snow is known by hydrologists as the “snow water equivalent” (SWE). Until recently, this was very difficult to quantify. There are only about 40 monitoring stations in Switzerland providing SWE data and the measurements are fairly infrequent, as they are time consuming. Teams of scientists have to dig holes in the snow right down to ground level to extract ice cores, which are then weighed.

...This new technique of combining actual measurements with models enabled the WSL to provide daily maps that show how much water the snow will yield at 350 different stations throughout Switzerland. Snow hydrological bulletins are then sent to flood forecasters....

Frozen Hinterstockensee seen from Stockhornbahn, Iglucamp on the left, shot by Chin tin tin, Wikimedia Commons, under the Creative Commons Attribution 3.0 Unported license

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