Natural Hazards
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2 / 2 0 0 7 ENVIRONMENT 4 ENVIRONMENT 2/07 NATURAL HAZARDS NATURAL HAZARDS IN THE ALPINE REGION Switzerland at a glance 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 com- pared 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. Switzerland lies in the temperate cli - Swiss Central Plateau is one of the most around 65,000 kilometres, and due to mate zone of the centre of western Eu - densely populated areas in Europe. the extreme differences in altitude of rope and borders on France, Germany, up to 4,000 metres over a relatively Austria, Liechtenstein and Italy. It’s ter - High levels of runoff small area between the Alps and the ritory totals 41,285 square kilometres Due to the prevailing westerly winds Central Plateau, floods can occur al - (km 2), of which almost two thirds are and the country’s proximity to the At - most everywhere in Switzerland. More - located in the Alpine region. The inten - lantic Ocean, the Mediterranean Sea over, the steepness of the terrain exac - sively developed residential and eco - and the North Sea, a lot of humid air is erbates erosion and hence, also, the nomic zone is concentrated on the rel - blown towards the Alps. Rain fronts of - risks posed by landslides and debris atively flat Central Plateau which only ten accumulate for days in front of this flows. Warmer periods, when the sea - accounts for 23 percent of the coun - meteorological barrier, giving Switzer - sonal snow and glacier melt in the try’s territory. Nestled between the Jura land above-average annual precipita - Alpine region coincide with intensive mountains in the north west and the tion volumes of 1,457 litres per square storms or orographic precipitation, are foothills of the Alps in the south, this metre (m 2). A good two thirds of this, particularly critical. In this situation, plain, which ranges from 50 to 100 i.e. almost 1,000 litres per m 2, is dis - rivers and lakes often break their banks kilometres in width, extends in a charged to other countries through an and flood the valley plains. north-east direction from Lake Geneva intricate network of streams and rivers. to Lake Constance. The mean water runoff in Switzerland Wide range of hazards is almost four times higher than that in in the mountains Densely populated Central Plateau the rest of Europe and the world. Thus, However, the mountain regions are The vast majority of Switzerland’s pop - a total of 40 billion cubic metres of wa - significantly more vulnerable to natur - ulation of around 7.5 million people ter flow into the Mediterranean, North al hazards than the Central Plateau. live in the lowland. In addition to the Sea and the Black Sea via the main Heavy snowfall and unfavourably centres of industrial production, the rivers, i.e. the Rhine, Rhone, Ticino structured snow cover create a risk of majority of the important service oper - (via the Po) and Inn (via the Danube). avalanches at high altitudes, while ations and the main road, rail and avia - This explains Switzerland’s crucial role heavy rainfall during the warmer sea - tion infrastructure, all of the major as a water reservoir for western Europe. sons can trigger landslides and debris cities, i.e. Geneva, Lausanne, Bern, flows. Rock fall and rock slides can also Lucerne, Zurich and Basle, are located Almost countrywide flood risk put both settlements and important here. Thus, with a population density Due to the extensive network of water transport routes at risk, as demonstrat - of almost 600 people per km 2, the courses, whose combined length totals ed, for example, by the blocking of the ENVIRONMENT 2/07 NATURAL HAZARDS 5 Land Use in Switzerland Settlement Agriculture (not including Alpine farming) Alpine farming Basle Lake Constance Rhine Forest Zurich Water bodies Glaciers, firn Reuss Other unproductive areas Aar Lucerne Berne Lausanne Lake Geneva Geneva Rhone Lugano Federal Statistical Office FSO, GEOSTAT / FOEN Gotthard motorway, a key cross-Alpine land, however when they arise they forests and water bodies, hazard map - road axis between northern and south - represent the natural hazard with the ping and the planning, construction ern Europe, in 2006. The above-average greatest potential for damage. Individ - and maintenance of protective struc - climate warming in the Alpine region ual areas such as Valais and the Basle tures – however they receive financial and the resulting thawing of the per - region are at greater risk from earth - and expert support from the federal au - mafrost and retreat of the glaciers will quakes than other parts of the country. thorities. The Federal Office for the En - cause greater volumes of loose material vironment is responsible for the strate - to be mobilized in the future, a devel - Safety as a public service gic management of these tasks and opment which represents an additional The protection of the population and guarantees safety at national level on threat to settlements, transport routes important material assets against nat - the basis of uniform standards. It is up and other infrastructure. Longer peri - ural hazards is provided as a public to the 26 cantons to decide whether to ods of drought also increase the risk of service by the state. In the federal state organize these tasks centrally or to del - forest fires, particularly in the south of of Switzerland, this task is perceived as egate some of them to the political mu - Switzerland. Overall, climate change is the joint task of the Confederation, nicipalities, of which there are over expected to increase the intensity of cantons and municipalities. The auth- 2,700 in Switzerland. Thus, the system precipitation and storms, prompting orities on all three levels work closely accommodates the cultures of political the need for more measures to limit the with each other in this area, which re - cohabitation which vary from region extent of the damage caused by floods, quires close cooperation. Thus, for ex - to region. hail and severe storms. Earthquakes ample, the 26 cantons are responsible tend to be a rare occurrence in Switzer - for the maintenance of the protection Beat Jordi 6 ENVIRONMENT 2/07 NATURAL HAZARDS HAZARD PREVENTION There is no such thing as absolute safety As a mountainous country with considerable variations in altitude over a relatively small area, Switzerland is particularly vulnerable to the various types of natural hazards. Swiss society is in a position to reduce existing risks to human life and material assets to an acceptable level, however there is no such thing as absolute safety. On the night of 23 August 2005, the extreme events, its discharge corridor houses on the alluvial fan bordered swollen Glyssibach torrent burst its in the village is being widened consid - directly on the old torrent bed. The narrow banks and discharged thou - erably to 18 to 21 metres and secured families affected by this measure found sands of tonnes of debris and mud into by means of massive dikes. An even alternative solutions and were compen - a neighbourhood of Brienz in the can - wider channel is needed in the flatter sated for the loss of land by the munic - ton of Bern. Following heavy rain estuary area where the Glyssibach tor - ipalitiy. throughout the Alpine foothills, nu - rent deposited its debris on a number merous landslides were triggered on of occasions in the past. For reasons of The renunciation of land use the steep slopes of the Brienzer Rot- space, it will be necessary to sacrifice in high risk areas horn mountain, the contents of which some of the existing development land As in Brienz, a row of 14 houses in were conveyed down to the valley at in this case as some of the destroyed Chippis near Siders on the river Rhone top speed by the mountain torrents. continued on page 8 Ten buildings failed to withstand this force of nature and were completely Flood damage in Switzerland between 1972 and 2002 destroyed by the deluge of debris and water from the Glyssibach, and a fur - ther 18 houses suffered extensive dam - age. Two people lost their lives on the night of the disaster, however the ma - jority of people who were taken by complete surprise by the event – and, in some cases, roused from their sleep – managed to make it to safety in good time. More space for mountain torrents Just a short time after the devastating debris flows, the Bernese cantonal au - thorities responsible for flood protec - tion in the region decided – in consul - tation with the federal authorities and the affected municipality – that some of the houses destroyed by the flood WSL should not be rebuilt in the same loca - tion. To create sufficient space for the As demonstrated by an analysis of flood damage between 1972 and 2002, large areas of torrent’s bed load in the case of future Switzerland are flood-prone. Each blue dot on the map marks a loss event. ENVIRONMENT 2/07 NATURAL HAZARDS 7 Swiss Air Force The destruction of part of Brienz village in the canton of Bern by debris flow from the Glyssibach torrent during the storm of August 2005. Flood damage in Switzerland between 1972 and 2005 annual damage (adjusted for inflation) cumulative damages (adjusted for inflation) The scale of the damage caused by annual damage cumulative damages floods is increasing. The storms in million CHF in million CHF of August 2005 – with heavy 3000 15 000 flooding in Central Switzerland and Bernese Oberland – were the most expensive extreme event ever 2500 suffered by Switzerland.