The ?Climate Adaptation Strategy for the Grimsel Area? responds to challenges resulting from the combination of i) climate change impacts on natural hazard potentials and ii) pre-existing socio-economic and socio-cultural context vulnerabilities.
The Grimsel area is characterised by high exposure to gravitational and hydrological hazard processes, such as rock fall, mudflows, torrential processes, landslides, avalanches, and floods through aggradation. In consequence of permafrost thawing and glacier retreat, different parts of the region have been affected by major natural hazard events involving mass movements on an annual basis and to an increasing extent in recent years. Due to the temperature-driven rise in elevation of the permafrost line, mobilisation of debris in consequence of glacier ablation, increasing likelihood of heavy rainfall events, and the rising snowline, it is expected that major mass movement events will become more likely also during the summer in the future.
Annual mean temperature in Switzerland has already increased by 2.0°C between 1864 and 2017, compared to 0.9°C globally (CH2018, 2018). According to the most recent Climate Scenarios for Switzerland 2018 (CH2018, 2018), until the end of the 21st century annual mean temperature over entire Switzerland may increase by up to 6.9°C since the pre-industrial era (5.4°C compared to the reference period 1981-2010) for the unabated emissions scenario RCP8.5. For the 2°C-compliant mitigation scenario RCP2.6, warming will likely be in the range of 2.1 ? 3.4°C above pre-industrial levels (0.6 ? 1.9°C compared to the 1981-2010 period). Even stronger warming is expected to occur in the summer season. In the long term, unmitigated climate change (RCP8.5) will likely cause mean precipitation over Switzerland to decrease during summer and to increase during winter. Depending on the region, projected median increase in winter precipitation by 2100 ranges from +12% to +22%, and the median decrease in summer precipitation ranges from -10% to -24%. It is estimated that under the RCP8.5 scenario the zero degree level will rise by 700 to 1050 meters in winter (compared to 1981-2010). This will result in a likely decrease of snowfall sums by more than -50% and a decline of mean winter snow cover by -80% at low elevations. There is robust evidence that there will be more frequent and intense heavy rainfall events, particularly in the winter half year, with the intensities of peak events showing the largest changes: for RCP8.5, rainfall amounts during day-long heavy precipitation events with 100 year return intervals are projected to increase by 10 - 25% until 2100. The combined effects of increasing winter precipitation, a rising share of rainfall instead of snow, and intensifying extreme rainfall events will have severe implications for the risk of flooding and other natural hazard processes.
The Swiss national analysis of climate-related risks and opportunities (Köllner et al., 2017) has identified increasing frequency and/or spatial extension of mass movements due to glacier retreat and permafrost thawing, including in areas that were previously not affected, as a priority climate change risk for several Swiss regions, including the Swiss Alps. Without adaptation measures, decreasing slope stability and more frequent mass movements are likely to increase the risk of damage to human lives and material assets (buildings, infrastructure, indirect damages, decreases in storage capacities of water reservoirs) to a considerable extent.
In the Grimsel area, high current problem pressure from mudflows and local flooding in parts of the municipal territories was an important driver for initiating development of the climate adaptation strategy. In their assessment of future challenges, the participating stakeholders concluded that threats caused by a range of hydro-gravitational hazards are likely to increase under conditions of progressing climate change, including an extension of hazard-prone periods into the summer season (Bender-Gàl et al., 2016). The resulting risks directly affect the only cantonal road, which is the main public transport connection in and out of the region, the secondary road system, buildings and settlements, the supply infrastructure (drinking water, power lines, telecommunication), and facilities related to hydropower production, which is a main economic asset of the region.
Climate change impacts on natural hazards are closely related to manifold issues of regional development in this peripheral rural area. Growing risks from natural hazard processes overlap and interact with other external pressures and socio-economic trends in force within the region, often exacerbating them. These non-climatic factors include: demographic change (rural out-migration, ageing of the population); limitations to settlement development due to natural conditions; limited public financial capacities for structural protection measures; impaired risk perceptions of the population (affecting perceived quality of life); dependence of attractiveness for tourism and of employment levels on continuity of the road connection. Climate-driven natural hazards influence these factors of regional development by affecting three key prerequisites of sustainable regional development, and by threatening their necessary balance, namely: i) transport connectivity and reliability of public infrastructure, ii) safety, and iii) quality of life.