The hazard situation in the Alpine country of Switzerland is influenced by the significant differences in altitude over a small area and relatively high precipitation volumes as compared with the rest of Western Europe. Floods, in particular, can arise almost everywhere as water run-off per square meter is almost four times the global mean.
Text: Beat Jordi
Switzerland lies in the temperate climate zone of the centre of Western Europe and borders on France, Germany, Austria, Liechtenstein and Italy. Its territory totals 41,285 square kilometres (km2), of which almost two thirds are located in the Alpine region. The intensively developed residential and economic zone is concentrated on the relatively flat Central Plateau which only accounts for 23 percent of the country’s territory. Nestled between the Jura mountains in the north west and the foothills of the Alps in the south, this plain, which ranges from 50 to 100 kilometres in width, extends in a north-east direction from Lake Geneva to Lake Constance.
Densely populated Central Plateau
The vast majority of Switzerland’s population of around 8.2 million people live in the lowland. In addition to the centres of industrial production, the majority of the important service operations and the main road, rail and aviation infrastructure, all of the major cities, i.e. Geneva, Lausanne, Bern, Lucerne, Zurich and Basle, are located there. Thus, with a population density of more than 600 people per km2, the Swiss Central Plateau is one of the most densely populated areas in Europe.
High levels of runoff
Due to the prevailing westerly winds and the country’s proximity to the Atlantic Ocean, the Mediterranean Sea and the North Sea, a lot of humid air is blown towards the Alps. Rain fronts often accumulate for days in front of this meteorological barrier, giving Switzerland above-average annual precipitation volumes of around 1,460 litres per square metre (m2). A good two thirds of this, i.e. almost 1,000 litres per m2, is discharged to other countries through an intricate network of streams and rivers. The mean water runoff in Switzerland is almost four times higher than that in the rest of Europe and the world. Thus, a total of 40 billion cubic metres of water flow into the Mediterranean, North Sea and the Black Sea via the main rivers, i.e. the Rhine, Rhone, Ticino (via the Po) and Inn (via the Danube). This explains Switzerland’s crucial role as a water reservoir for Western Europe.
Almost countrywide flood risk
Due to the extensive network of water courses, whose combined length totals around 65,000 kilometres, and due to the extreme differences in altitude of up to 4,000 metres over a relatively small area between the Alps and the Central Plateau, floods can occur almost everywhere in Switzerland. Moreover, the steepness of the terrain exacerbates erosion and hence, also, the risks posed by landslides and debris flows. Warmer periods, when the seasonal snow and glacier melt in the Alpine region coincide with intensive storms or orographic precipitation, are particularly critical. In this situation, rivers and lakes often break their banks and flood the valley plains.
Wide range of hazards in the mountains
However, the mountain regions are significantly more vulnerable to natural hazards than the Central Plateau. Heavy snowfall and unfavourably structured snow cover create a risk of avalanches at high altitudes, while heavy rainfall during the warmer seasons can trigger landslides and debris flows. Rockfall and landslides can also put both settlements and important transport routes at risk, as demonstrated, for example, by the blocking of the Gotthard motorway, a key cross-Alpine road axis between northern and southern Europe, in 2006. The above-average climate warming in the Alpine region and the resulting thawing of the permafrost and retreat of the glaciers will cause greater volumes of loose material to be mobilized in the future, a development which represents an additional threat to settlements, transport routes and other infrastructure. Longer periods of drought also increase the risk of forest fires, particularly in the south of Switzerland. Overall, climate change is expected to increase the intensity of precipitation and storms, prompting the need for more measures to limit the extent of the damage caused by floods, hail and severe storms. Earthquakes tend to be a rare occurrence in Switzerland, however when they arise they represent the natural hazard with the greatest potential for damage.
Safety as a public service
The protection of the population and important assets against natural hazards is provided as a public service by the state. In the federal state of Switzerland, this task is perceived as the joint task of the Confederation, cantons and municipalities. The authorities on all three levels work closely with each other in this area, which requires close cooperation. Thus, for example, the 26 cantons are responsible for the maintenance of the protection forests and water bodies, hazard mapping and the planning, construction and maintenance of protective structures – however they receive financial and expert support from the federal authorities. The Federal Office for the Environment (FOEN) is responsible for the strategic management of these tasks and guarantees safety at national level on the basis of uniform standards. It is up to the 26 cantons to decide whether to organize these tasks centrally or to delegate some of them to the political municipalities, of which there are 2,324 (status: 1.1.2015) in Switzerland. Thus, the system accommodates the cultures of political cohabitation which vary from region to region.
Download this edition (PDF, 5 MB, 20.05.2015)2/2015 Living with Natural Hazards
Last modification 20.05.2015