The degradation of mountain permafrost is an additional consequence of persistently high temperatures which can lead to slope instabilities which threaten settlements and communication routes. … In many mountainous regions, tourist resorts such as those in the Alps have spread into high-risk areas, and these will be increasingly endangered by slope instability (1).

On north facing slopes in the Alps, permafrost occurs at altitudes above 2600 m, on south facing slopes above 3000 m, and in zones with long-lasting avalanche snow at altitudes several hundred metres lower (5). Permafrost is also sensitive to snow cover, topography, aspect and ground surface material (6).

Recent studies show ongoing permafrost warming in the European Alps: during the twentieth century, permafrost warmed by 0.5 to 0.8°C in the upper tens of metres (7), particularly at higher elevations, with accompanying thickening of the seasonal active layer (8). Changes in snow cover thickness and duration also affect sub-surface temperatures and permafrost distribution (7,8); therefore decreasing snowfall will promote permafrost degradation, irrespective of changes in air temperature.

The European Alps is sensitive to such changes because it is located at the boundary between different moisture source regions, its glaciers and permafrost are in long-term decay, and hazardous events can readily impact on areas of high population density in alpine valleys (13).

The geomorphological and wider landscape impacts of the 2003 and 2005 events can be considered analogous to the probable hazardous impacts of future climate changes in the eastern European Alps, under which meteorological variability will be more common. In turn, this has implications for risk management in the Alps (13).

Global warming and mountaineering

Glacier retreat and permafrost degradation seem to be the two most important processes in the context of global warming and mountaineering. Both provide additional rock material for different kinds of mass movement processes. Unstable material provides new potential starting zones for different kinds of mass movements such as debris flows, landslides, or rockfall. Numerous classical ice climbs in the Eastern Alps have become heavily affected by rockfall and falling stones as well due to rocks melting out at the ice margins (26).

Both glacier retreat and permafrost degradation can also reduce morphodynamics locally, thereby decreasing the occurrence of natural hazards (27). Hence, it cannot be generally stated that the mountains are becoming more dangerous throughout. There is still little known about the frequency of the mentioned hazard events, and to date there are no time series available to prove that these events have become more frequent in the long run (27).

The impact of a hot summer: 2003

The summer of 2003 was characterized by the hottest temperatures in the last 500 years in Central Europe (9) and the warmest summer in a 1250 year long record for the European Alps (10). Summer precipitation in Austria and Switzerland was only 50 per cent of average (11), which had also been preceded by a dry spring (February–June).

In 2003 the thaw depth in permafrost on bedrock slopes was twice the average of previous years and indicates a strong coupling between atmospheric and ground temperatures (7). Permafrost degradation set into action by this warming was reflected in increased rock-fall activity throughout the Alps during summer 2003 (7). In particular, localities near the lower elevational limit of the discontinuous permafrost are very sensitive to changes, and respond with a short time lag (of days–months). For example, a large rock-fall event at the elevation of the lower permafrost boundary on the Matterhorn (Switzerland), July 2003, revealed weakened interstitial ice at the back of the rock-fall scar (12). Large-scale responses to warming permafrost, such as deep-seated slope instabilities, may show a delay of decades or centuries (7,8).

The observed increase in periglacial and glacial hazards, as during the 2003 event, is concentrated in high-altitude areas where it impacts on small settlements and mountaineering/skiing infrastructure (paths, huts). Public awareness of these mountain hazards (as opposed to floods and snow avalanches) is generally low. Despite a low direct effect on society, these high-mountain hazards increase the availability of easily mobilized debris and so increase future hazard risk. The 2005 event showed the connectivity between process chains or cascades resulting from such mountain-hazard events, which lead in turn to high sediment transport through landslides and other processes, and their impacts on valley settlements (13).

The impact of heavy downpour: 2005

In August 2005, Central Europe and especially the Alpine region was affected by severe floods accompanied by river-bank erosion and sediment transport, as well as debris flows, rock falls and landslides in the smaller catchments (14). These events caused the most catastrophic flood damage in the last 100 years with respect to loss of life and damage to infrastructure, communication routes and agriculture (15). In Switzerland, the August 2005 event caused one quarter of all damage by floods, debris flows, landslides and rock falls recorded since 1972 (16).

In Austria alone, 115 debris flows and 111 other landslides were recorded (17), mainly with medium to high sediment volumes. A few debris-flow events transported more than 100,000 m3of sediment (14). A substantial part of the sediment load (debris and woody debris) accumulated as torrent fans in the main valleys. Some of the debris flows delivered their sediment load into mountain rivers and contributed to the high sediment transport in the river downstream, in addition to the sediment produced locally (14). The strong geomorphological activity during the flood event resulted in changes to channel courses, enhanced bank overtopping and sediment deposition outside the main channels. This led to substantial flood damage on inhabited areas and infrastructure along the river channels (14).

The 2005 event caused losses of up to 555 million Euro across Austria, of which 442 million Euro occurred in the western states of Austria (18).

Austria uses design events with a 100 year recurrence interval for floods and 150 years for debris flows. The 2005 event was far beyond these design events and therefore historical experience, meaning that the record of past events is no longer sufficient for hazard assessment. ... The role of climate change in the Alps, which the 2003 and 2005 events probably prefigure, has significant implications for hazard triggering and mitigation (13).

In 2005, Austria spent a total of EUR 122 million on preventive measures against torrential flooding, avalanches and erosion, with the federal government providing EUR 69 million of that (2).

The impact of wildfires

Rockfall risk is related to the risk of wildfires. Increased rockfall activity of rather smaller rock blocks is recognizable during as well as after the wildfire. The destabilization of small rock blocks and the burn of tree roots may also cause the destabilization of larger rock masses (36).

Future projections mostly indicate an overall decrease in snow depth and snow cover duration at lower elevation, but the probability of occurrence of occasionally large snow precipitation events is projected to remain possible throughout most of the 21st century (29). An overall 20 and 30% decrease of natural avalanche activity in the French Alps is estimated for the mid and end of the 21st century, respectively, under a moderate (A1B) scenario of climate change, compared to the reference period 1960 – 1990 (34). The overall number and runout distance of snow avalanches is projected to decrease in regions and elevations experiencing significant reduction in snow cover (35)

Avalanches involving wet snow are projected to occur more frequently during the winter at all elevations due to surface melt or rain-on-snow (34, for the French Alps).

In summary, there is medium evidence andhigh agreement that observed changes in avalanches in mountain regions will be exacerbated in the future, with generally a decrease in hazard at lower elevation, and mixed changes at higher elevation (increase in avalanches involving wet snow, no clear direction of trend for overall avalanche activity) (29).

• Improve public preparedness and personal responsibility by encouraging participation in emergency planning. To properly inform the public, risk management plans must address both emergency preparedness and early warning systems.
• Incorporate climate change adaptation into spatial planning. A few examples to create a sustainable regional development that is less vulnerable to natural hazards are: financial incentives, establishing hazard zones, setting appropriate construction standards of buildings and infrastructure in risk areas, keeping endangered spaces free of development, and performing hazard assessments through the use of hazard mapping.
• Involve local stakeholders in a risk dialogue. The dialogue includes meetings between important stakeholders, such as land and real estate owners, as well as those responsible for infrastructure and the public sector.
• Encourage cross-border networking on integrated risk management.
• Encourage a ‘common language’ and harmonised procedures when developing and using hazard maps.
• Increase the size of flood plains, floodwater conduits and basins. Governments need to consider multiple uses of the same land and consider strict legal binding instruments that ensure a priority for flood retention areas is given.
• Think of flood risk management in terms of an entire river basin to find solutions that are sustainable. Horizontal and vertical cooperation between all levels of government and the private sector are essential.
• When planning for natural hazard risks consider all the environmental risks within a defined area. Natural hazards—floods, droughts, landslides—generate risks that are interrelated and so should be addressed jointly.
• Use risk-management tools to explore the social and economic consequences of various adaptation measures. Risk planning tools allow for the integration of a wide range of strategies that reduce the risks of natural hazards, including spatial planning instruments, technical protection structures, specific protection measures for individual buildings and early-warning systems.
• Support the collection and interpretation of local climate change data.