0941-B1
Peter Greminger[1]
For centuries, avalanches, mudslides, falls of stones and rocks, landslides and floods have all been part of the landscape of the Alpine region and of the way in which the landscape has changed. The increases in settlements and development mean that about a million people now live in the Swiss Alpine region, and this population is repeatedly threatened locally by natural hazards. Thanks to the efforts made by the state, the threat of avalanches and flooding has been reduced. However, the risk of damage to property from natural disasters has increased. Therefore, the prevention of any further increase in the risk of such damage represents a considerable challenge for the future. Possible measures include spatial planning, conservation of protection forests, early-warning systems, organizational measures, protective structures, prevention measures to deal with disasters, and measures to restore normal conditions after natural disasters. Economic, ecological, safety and social aspects must all be taken into account.
Global statistics, as well as those for Switzerland, show that damage from extreme weather events occurs repeatedly in places where avalanches, mudslides, rockfalls, landslides and flooding have for centuries been part of the landscape. In many cases, we ourselves have increased the risk to human beings posed by natural hazards.
New areas have been opened up in the Alps for settlements, recreation and transport, although these areas had previously been barely accessible, and had been considered to be extremely dangerous. This has been made possible by the construction of road and rail tunnels several kilometres in length, and of galleries, bridges and cable railways, and also by the use of avalanche protection structures, nets to give protection from rockfalls and other protective barriers. About a million people in Switzerland now live in areas that, at the local level, are repeatedly threatened by the forces of nature and suffer damage.
The municipality of Brienz, in the Bernese Oberland, provides an example of how the development of settlements between 1870 and 1993 has enlarged the areas at risk from mudslides and from rivers overflowing their banks (see Fig. 1).
Fig. 1 Hazard situation in the municipality of Brienz (Bernese Oberland) - comparison between 1870 and 1993
In exploiting the Alpine region, human civilisation has always exposed itself to the forces of nature(see Fig. 2). Extreme weather conditions, combined with the steepness of the terrain and its susceptibility to erosion, create distinctive dynamics of natural processes. The hazard potential has changed dramatically over the past hundred years. Until about 1900, the threat was primarily due to severe over-exploitation of the mountain forests, to the extent that settlements and transport routes were inadequately protected against avalanches, rockfalls, landslides, flooding and mudslides. Nowadays, the damage potential is continually increasing, mainly because of increasingly intensive exploitation of areas at risk, and the related appreciation in the value of assets in these areas.
In mountainous areas where, in the past, avalanches and mudslides generally only presented a threat to seasonally used Alpine buildings, grassland and crops, buildings can now be found which are occupied throughout the year, together with important routes for passenger and freight traffic, and tourist infrastructure.
In addition, the threat posed by climate change is increasing the hazard potential. Although there is not yet any exact scientific proof, present-day understanding of climate processes suggests that warming of the climate will be accompanied by extremely strong winds, and (especially on the South side of the Alps) by heavy precipitation. Increasingly severe flooding in the winter and during transitional periods is also expected.
Fig. 2 Fatalities resulting from avalanches, flooding, mudslides and landslides between 1937 and 2000. Over the past 30 years, on average about 10 people have lost their lives each year in accidents caused by natural disasters in settlements or on roads. If deaths from high-risk activities and fashionable sports such as off-piste skiing and canyoning are included, the total increases to about 40 fatalities per year (source: Swiss Federal Institute for Forest, Snow and Landscape Research/Swiss Federal Institute for Snow and Avalanche Research)
In view of current changes in legislation relating to forestry and to water management, together with the development of the insurance business over the past hundred years, the authorities, insurers and voluntary organisations have developed procedures to ensure protection from natural hazards, and to cope with natural disasters. In addition, the fire brigade and civil defence forces are now trained and equipped to limit the damage from natural disasters by means of rescue and evacuation operations, and to ensure a rapid return to normal in the affected area. Sound emergency planning is a prerequisite if such procedures are to be effective.
Training of the public services for natural hazard protection is linked to the call for improved safety in relation to natural hazards. This demand is reinforced by the fact that the collective safety of the population is accorded greater priority than the risk to individuals.
As can be seen from the case of the Gotthard railway line (Fig. 3), the requirements for safety have changed over the past hundred years, influenced by the increase in potential damage and natural hazard risk.
Fig. 3 Changes in the requirements for safety for the Gotthard railway, from about 1900 to about 2000 - a
Fig. 3 Changes in the requirements for safety for the Gotthard railway, from about 1900 to about 2000 - b
The current increase in the frequency of extreme weather events and their damaging consequences reflects the fact that even highly developed safety technology cannot guarantee absolute protection from natural hazards.
Furthermore, in a characteristically Alpine region such as the Grisons, 450 natural hazard sites have been identified along the 1,600 km of its road network. For financial, technical and ecological reasons, it would be impossible to provide protection from all hazards by means of structural measures.
However, public awareness of the limits of technical feasibility is decreasing. Nowadays, even in mountainous regions, the public expects to have roads that can be used safely, around the clock, despite climatic and topographical constraints.
The declared aim of the authorities is to adapt land-use planning to natural hazards with the highest priority, despite the fact that it is not possible to ensure safety for everyone and for everything. This is not only a matter of resources, which are limited, but also a question of space and of what already exists in a densely populated Alpine country such as Switzerland. It is of great importance to know where natural processes may become a hazard for human beings. Only if we know where a danger may arise can we protect ourselves against it. A stepwise approach is to be recommended.
The first step is therefore to identify the natural hazards, in order to adapt spatial planning to them. It is necessary to distinguish between the knowledge that is required to give a general overview at the level of regional master plans and the detailed information relating to individual plots that provides the basis for a municipal hazard zone plan. For a master plan, the hazard information map is generally sufficient, whereas to demarcate a hazard zone, an accurate hazard map (based on expert opinion) is necessary.
Different natural hazards need to be assessed in terms of their probability of occurrence and severity (intensity), as shown in Fig. 4. For this purpose, it is necessary to study not only individual hazard processes, but also the interactions between processes such as mudslides and avalanches. By combining the potential hazard and community vulnerability, conclusions may be drawn with regard to the possible level of damage.
Fig. 4 Hazard levels for assessment of the danger of flooding
The results of the hazard assessment serve as the basis for the third step: taking natural hazards into account in spatial planning. The regional administration is responsible for preparing the master plan, whereas the municipalities are responsible for local planning, considering natural hazards. This is normally done by referring to hazard maps in land-use planning at the level of individual plots, and involves regulating land use on the basis of risk. In areas that have already become densely populated, and which have little potential for development, the pressure on the authorities to take risks is greater than in areas where there is still considerable potential for development (see Fig. 5).
The final step consists of providing suitable protection from natural hazards in cases where people and/or property of considerable value are at risk from avalanches, landslides, erosion, falls of ice or rocks, or flooding, and the possibilities offered by spatial planning have been exhausted. This involves the use of forestry measures, such as conservation of protective forest; organisational precautions, such as early-warning systems, evacuation and road closure; structural measures, e.g. providing protection from avalanches and floods; and appropriate emergency planning.
In a country such as Switzerland, characterised by lakes, mountains and forests, the possibilities of land-use planning are limited, although they are accorded very high priority. This is one of the reasons for the sharp increase in the value of property at risk and for the fact that nowadays, it is necessary to consider the acceptability and reasonableness of natural hazard risks, rather than expecting complete protection.
Fig. 5 Procedure for taking natural hazards into account in land-use planning
Experience accumulated over the past 50 years in dealing with avalanche risks and the associated land-use planning gives grounds for optimism, although in this case the problem is spatially restricted compared with that of flooding. The large number of fatalities and buildings damaged by avalanches over the centuries shows that even in the past, buildings were constructed and occupied in locations exposed to risks. Often, buildings that had been destroyed were rebuilt on the same foundations. The risk was obviously accepted, despite the danger experienced.
In the winter of 1999 - despite the increased number of people (tourists and local population) and buildings (hotels etc.) in the affected regions, a denser road network and increased traffic - much less damage (in terms of people and property) was caused than in the winter of 1951. The closure of roads and railway lines and the evacuation of buildings in yellow and blue zones had positive effects. As a result of the consideration given to hazard maps, the number of buildings damaged was noticeably lower. The avalanches of the winter of 1999 demonstrated the value of consistent, preventive, integrated protection against natural hazards.
Extreme events threaten human life, affect man-made structures and disturb human activities. The increase in the vulnerability of people and structures in cases of disaster is inextricably linked with technological advances.
The need for security within modern society is characterised by diverse categories of risk (Table 1).
Table 1 Risk categories
|
Risk category |
Examples |
|
Global risks |
Risks of disaster geopolitical climatic demographic religious biological |
|
Local risks |
disasters major damage to communities/individuals environmental damage economic damage |
|
Political and legal risks |
social/cultural/ethical changes administration of justice changes in political/legal framework (federal government, canton, municipality etc.) inconsistent political decisions |
|
Financial risks |
excessive demands on the community changes in interest rates, tax revenues, inflation |
Given the variety of categories of risk, it is obvious that protection from natural hazards can only be one component of public-sector risk management oriented towards sustainability. Technical feasibility, ecological factors and, increasingly, economic considerations all impose limits on the reduction of risks, including the risk posed by natural hazards to human beings, animals and property. Neither the public sector nor private individuals can now afford to meet the cost of minimising the residual risk of natural hazards.
In the case of processes such as avalanches and rockfalls, life-threatening situations occur suddenly, and populations are subjected to an unacceptable risk. Therefore, in such cases, measures such as avoidance and prohibitions are of the utmost importance.
In the case of slow-acting processes such as flooding, there is normally little danger to life, though there is considerable potential for damage to property. Sites by inland waters have always been attractive for the establishment of settlements, offering water power and the transportation and recreational advantages of lakes. The risk of occasional flooding was accepted and prepared for. The advantages enjoyed in times free of flooding were greater than the losses caused by occasional flood damage. In the past, damage was limited by appropriate measures such as cautious use of basements and the preparation of platforms. Nowadays, awareness of and commitment to such extraordinary situations is decreasing, as is individual responsibility; instead, complete protection is expected.
Before the introduction of revised legislation on water management and on forestry in 1991, the only basis for land-use planning was the avalanche hazard maps. No attention was paid to any other types of natural hazard. In cases where human beings were exposed to a risk of natural hazard, since no hazard zones had been demarcated, the problem of a life-threatening hazard was resolved between the authorities, the insurance companies and the landowners concerned. From the present point of view, natural hazards are properties of a specific location and have to be taken into account when determining land use. Adverse consequences are purchased with the associated land and must therefore be borne by the landowner. In the use of land, opportunities and risks are closely linked, so they must be borne by the individual. It would not be fair if the potential for profit were exploited by the individual, while the risks had to be borne by the authorities, insurance companies and the state.
According to the report to the Standing Committee of the Alpine Convention on the 1999 winter of avalanches, the carrying capacity of the fragile Alpine ecosystem and the feasibility of achieving an appropriate standard of safety at Alpine tourist sites have reached their limits. Therefore, even greater importance should be attached to calls for sustainable development in mountainous areas.
Although planning the future of the Alpine region is not simple, it is ultimately a matter of maintaining mountain areas as attractive places to live in. This means preserving an intact landscape and allowing only forms of exploitation that are appropriate to the site and to the risks, with the best possible protection of nature and landscape.
On 15 August 1997, a heavy storm broke over the region of Sachseln in Central Switzerland. In just two hours, up to 150 litres of water fell per square metre. Over 400 landslides from the steep mountain slopes were set in motion, many of them taking the form of mudslides in the stream courses. This material mixed with the raging floods, and vast volumes of water and mud destroyed the village of Sachseln, blocked roads, rail links and infrastructure supply lines and buried extensive areas of fertile cultivated land. The total cost of the damage incurred was in excess of CHF 100 million. In order to reach a better understanding of the links between forest vegetation and the landslides, the Swiss Research Institute for Forest, Snow and Landscape (WSL) was commissioned to carry out studies on the limits of the influence of forest in such circumstances. The following conclusions were reached in these studies:
The state of the forest plays an important role: in the forested part of the study area, there were ten times more landslides in locations with poor quality forest (see Fig. 6).
Under otherwise comparable conditions, there were significantly fewer - one third fewer - landslides in the forested areas than in the non-forested areas (see Fig. 7).
Stable forest stands comprising mosaics of trees of different species, ages and heights offer the best protection.
Fig. 6 The influence of the state of forests on the number of landslides.
Fig. 7 The influence of forest vegetation on the size of landslides. Thanks to its extensive root networks, forest cover reduces the size of landslides and thus makes an important contribution to the bedload balance in the water-shed area.
Good forest quality can only be achieved on a permanent basis through constant maintenance and regeneration. Specific interventions should be carried out according to the principles of minimum protection forest maintenance in areas where such maintenance is necessary and can produce lasting effects.
The following decision aid is intended for use by forestry services in their efforts to ensure minimum protection forest maintenance (see Fig. 8). For purposes of evaluation, a systematic monitoring system is also being developed, which will be implemented by foresters at selected representative control points. The aim of this monitoring is to manage the natural development of the forest in such a way as to guarantee uninterrupted fulfilment of the protective function while minimising the work involved.
Fig. 8 Decision aid for implementation of minimum protection forest maintenance measures
There is a need to stem the increase in damaging events by means of an appropriate protection strategy, based on the three key factors of sustainability: "social solidarity", "a favourable approach to the environment" and "economic capacity".
Fig. 9 Overall protection strategies should provide balanced protection against natural hazards
For reasons of sustainability and of safety, it is essential that the following protection measures be applied (in descending order of priority):
Avoidance of areas exposed to the risk of natural hazards
Conservation of forests with a protective function
Land use adapted to the actual risk
Prevention of increased risks along transport routes and in settlements as a result of intensified use and appreciation in value
Organisational measures, such as early-warning systems, evacuation, road closure, etc.
Maintenance of existing protection structures
New protection structures.
Complete protection from natural hazards is not possible, and natural disasters will continue to be a threat to life. This means that, in the future, solidarity will be required between victims and those unaffected, and between areas exposed to lesser and greater risks (e.g. mountain areas). Companies providing property insurance have an important part to play in this process.
The following measures are to be recommended:
Early identification of natural hazards and consideration of such hazards in spatial planning
Improvements to national and international communications through increased use of internet technology
Forward-looking measures to avoid injury to human beings and damage to settlements and infrastructure using appropriate means, such as land-use planning, maintenance of protection forest, early-warning systems, introduction of organisational measures (e.g. evacuation), dialogue on risk, and construction of protection structures, maintaining an overall site-specific view, with an awareness of costs and of the environment
Promotion of knowledge to ensure risk-adapted land use, taking into account safety, economic, ecological and social criteria
Promotion of dialogue on risk
Production of a single cadastral register of hazards and protection measures, including all natural hazards
Consistent, targeted support for sustainable development, involving reduced environmental impacts due to human beings, and careful use of scarce, non-renewable raw materials.
Borter, P. 1999: Risikonalyse bei gravitativen Naturgefahren, Methode. Bundesamt für Umwelt, Wald und Landschaft (BUWAL), Berne
Bundesamt für Forstwesen und Eidg. Institut für Schnee- und Lawinenforschung: 1984 Richtlininien zur Berücksichtigung der Lawinengefahr bei raumwirksamen Tätigkeiten.
Bundesamt für Umwelt, Wald und Landschaft (BUWAL) 1997: Empfehlungen zur Berücksichtigung der Massenbewegungsgefahren bei raumwirksamen Tätigkeiten
Bundesamt für Umwelt, Wald und Landschaft (BUWAL) 2001: Bericht zum Lawinenwinter 1998/1999 im Auftrag des ständigen Ausschusses der Alpenkonferenz. SRU-323 - D
Greminger, P 2003: Bericht über die Unwetterschäden im Alpenraum in den Jahren 2000 und 2001 Alpenkonvention. In preparation (2003).
Heinimann, H. R. et al. 1998: Methoden zur Analyse und Bewertung von Naturgefahren. Umwelt-Materialien Nr. 85, Naturgefahren. ed. Bundesamt für Umwelt, Wald und Landschaft (BUWAL), Berne
Rickli, Ch.; 2001: Untersuchung zum Einfluss der Vegetation auf oberflächennahe Rutschprozesse anhand der Unwetterereignisse in Sachseln OW; (2001). Birmensdorf (WSL), Bern (BUWAL)
| [1] Director of Protection
Forest and Natural Hazards Sector, Swiss Forest Agency, Swiss Agency for
the Environment, Forests and Landscape (SAEFL), CH-3003 Berne, Switzerland.
Email: [email protected] |