Vulnerabilities - Present risk of landslides

In the last two years Sweden has suffered several landslides with consequences that could have been very serious. Heavy precipitation and increased flows in watercourses as well as raised and variable groundwater levels will increase the risk of landslides. The increased risks will arise principally in areas where there is already a high risk today. This applies to the area around Lake Vänern, the valley of the Göta Älv river, eastern Svealand and almost the whole of the east coast (1).

It is estimated that more than 200,000 buildings are located close to water in areas where the risk of landslides will increase. Local conditions dictate where the risks will be greatest (1).

Over 55 large landslides, with a spread of at least one hectare, have occurred in Sweden over the past 100 years. Major landslides include the Surte landslide in 1950, the Göta landslide in 1957 and the Tuve landslide in 1977, plus the slide in Vagnhärad in 1997. The Surte, Göta and Tuve slides all claimed lives. The landslides caused immense damage primarily to buildings, but also to infrastructure. In the Göta Älv valley, shipping is often affected by underwater slides. The direct costs for the landslide in Vagnhärad have been calculated at SEK 120-130 million (1).

In December 2006, a major landslide occurred south of Munkedal. The slide covered a stretch measuring 550 metres long and 250 metres wide in a valley along which the E6 road and the Bohus rail line run. The soil in the valley, which contains quick clay, shifted around 20 metres sidewards and 7 metres downwards at its peak. Several cars were caught up in the landslide and some people were injured. The landslide caused serious damage to the road and railway, as well as telephone cables embedded in the banks (1).

The most likely soils to suffer landslides are marine clays which, due to rising land levels, have risen above sea level (quick clay). Particularly susceptible areas include the Göta Älv valley and other valleys in western Sweden. The topography of the land along the Göta Älv today has largely been formed through a number of major landslides. Clays inclined towards landslide can also be found in the Stockholm area, along the Norrland coast and in many other locations around the country. Slides on sand and silt slopes are common in the valleys of the large Norrland rivers (1).

Vulnerabilities - Future risk of landslides

Climate change with heavier and harder precipitation, as well as changed ground water levels, increases susceptibility to land collapse, landslide and erosion. The southwestern/western parts of the country and stretches of the east coast are particularly exposed. Low developments in areas susceptible to landslide are most at risk. In other areas the risk is falling as the snow melt season is becoming longer and the spring flood and high flows are decreasing in magnitude (1).

The risk of landslides is predicted to increase in many parts of Sweden. Towards the end of the century, it is estimated that around 220,000 properties will be situated in areas prone to landslides. The value of these amounts to almost SEK 320 billion. The cost of damage to electrical, water and sewage systems has been estimated at approximately SEK 15 billion. The value of the forest and arable land that is situated in areas where there is a risk of landslides is approximately SEK 14 billion and SEK 1.5 billion respectively (1).

According to the Swedish Geotechnical Institute's statistics for the river Göta älv, at least 2% of the stretches susceptible to landslide (clay-rich areas) will suffer landslides in a 50-year time span (Swedish Geotechnical Institute, 2007). If this scenario should apply to the entire country, then 4% of the areas susceptible to landslide would suffer landslides during the next 100 years. According to the above calculations, this corresponds to property values of about SEK 12 billion plus water supply and sewage systems, forestland and farmland at a value in excess of SEK 1 billion (1).

Adaptation strategies

It has been shown in case studies that preventive measures in the vast majority of cases cost significantly less than if a landslide occurs, even just a small landslide. It is therefore important for society to implement measures at those locations where the risk of landslides is judged to be great (1).

References

The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for Sweden.

1. Swedish Commission on Climate and Vulnerability (2007)