Thick snow cover raises spring flood risk

Spring flowers like these crocuses prove their resilience despite the snow Keystone

The heavy precipitation on the north side of the Alps over the past few days has left more snow in some parts as there was in the record winter ten years ago.

The Institute for Snow and Avalanche Research in Davos says there is a risk of serious flooding in the coming months, as there was in 1999.

The research institute said a few of its weather stations have registered record amounts of snow, many others were close to all time highs and nearly all reported above average levels.

Compared to other extreme winters in the post-war period, there are no large regional differences this year, the institute said.

In a 24-hour period at the weekend, 24 centimetres of new snow fell on the Grimsel Pass, making the snow there more than four metres thick.

Three factors are decisive whether the spring snowmelt will lead to a repeat of the 1999 natural disaster, which cost an estimated SFr580 million ($507 million) in damage.

The snow’s water content plays a role, as does a combination of rain and relatively warm spring temperatures at high altitudes, according to the institute. Also important is new snowfall in spring, which happened in 1999 and could occur again this year.

Global warming has increased the likelihood of periods of intense precipitation, which was confirmed by a report commissioned by canton Bern last year.

The report added that floods in future could be worse than the 1999 event or the summer flood of 2005, which caused more than SFr2 billion in damage.

Under water

In the worst-case scenario, large areas of the canton could be under water for weeks, damaging infrastructure such as power plants and sewage treatment facilities as well as cutting off entire valleys.

Also cause for concern is the fact that the Swiss authorities still do not have a big picture of all the areas potentially at risk. So-called hazard maps being prepared by each canton will not be complete before 2011.

The maps are key to limiting flood damage since it will ban building in areas considered at high risk.

Flood control

The data included in the maps will also put pressure on communal and cantonal authorities to ensure that existing structures located in these areas are reinforced to withstand floods.

Since the 1999 natural disaster, many cities and towns have invested in flood control projects. The city of Lucerne, which suffered from an event in 2005, is investing SFr23 million to protect its old town.

Another lakeside town – Thun in canton Bern – is preparing for a final test on Tuesday of a more than one-kilometre-long, SFr53.5 million tunnel built under the city. The authorities can divert more than 100 cubic metres of water a second through the tunnel to regulate the amount flowing into the River Aare from Lake Thun.

Despite the flooding fears, the institute in Davos cautions that the unpredictability of a warm southern wind known as the Föhn makes any forecasting difficult.

A strong Föhn sweeping over the Alps could start the snowmelt process early, thereby reducing the flood risk, it said.

swissinfo

Recent floods

August 2007: Flooding. Total cost more than SFr200 million.

June 8, 2007: Three people died in flooding in Huttwil and Eriswil (canton Bern).

August 21-23, 2005: Eight people died after heavy rainfall and flooding in Bern and east and central Switzerland. Many road and rail connections were washed out, with the villages of Engelberg and Lauterbrunnen cut off. The damage came to SFr2.5 billion.

October 14/15, 2000: Persistent rain in canton Valais led to landslides and flooding. Sixteen people died, including 13 in the village of Gondo. The bill came to SFr500 million.

May 15, 1999: Damage estimated at SFr580 million was caused after storms in several regions, including Bern, Thun, Rheinfelden and Lake Constance.

September 24, 1993: After heavy rainfall, the River Saltina burst its banks, causing severe damage in the town of Brig. Two people died, with damage estimated at SFr600 million.

Summer 1987: Eight people died after storms in Poschivao and the Reuss plain in canton Uri. Damage totalled SFr1.3 billion ($1.09 billion).