Leggi in italiano

A landslide above the Chambon lake and the Chambon tunnel, by the Lautaret pass in Mont-de-Lans, near Les Deux Alpes, eastern France, on July 5, 2015. Credit: Philippe Desmazes/AFP via Getty Images.

Landslides put lives at risk and cause substantial damage to settlements, but it’s still unclear how they will be affected by climate change. To find out, a study has simulated how a past extreme event could have happened differently in a warming climate. The results suggest that without efforts to cut greenhouse gas emissions, the area affected by landslides could grow by 45%. But also that creating more climate-resilient forests could help to reduce the hazard – especially if paired with emissions reduction1.

In June 2009, three days of heavy rainfall and thunderstorms in Austria triggered more than 3,000 landslides in the Feldbach district in the South–Eastern Alps. A state of emergency was declared and houses had to be evacuated.“What impact would an event like this have in a warmer climate,” asks Giuseppe Zappa, researcher at the Institute of Atmospheric Sciences and Climate, National Research Council of Italy, one of the authors of the study. “Landslides depend on local, geographical factors such as terrain and vegetation, but are triggered by meteorological events, and many of these factors are affected by climate change.”

To answer the question, the team integrated data from the 2009 landslides with global climate and local, high-resolution models, and adopted an event storyline approach. First they simulated the 2009 event as it happened, and then they did so again using different storylines, i.e. varying conditions. Using past events to characterise future scenarios has been highlighted by the Intergovernmental Panel on Climate Change as an effective strategy to communicate the risks posed by climate change, as it references situations that people may still remember vividly.If a 2009-like event were to happen in a climate that was 4°C warmer – the worst possible scenario – the area affected by landslides could be up to 45% wider than today. “We found that, in this scenario, the events that trigger intense summer rainfall in Austria may actually happen less frequently,” continues Zappa. “However, the increase in intensity would greatly surpass this reduction.”

For all the storylines, the key to limiting future landslides is keeping carbon emissions within the Paris Agreement. That would cause the area affected by landslides to increase by less than 10%, but these effects could be compensated by improving the root system of local forests – replacing spruce trees with broad-leaf species – and by increasing forest cover. These changes in land management were considered beneficial in all the storylines.

There is still uncertainty about how global warming will affect soil moisture. The study points out that higher temperatures may cause water in the soil to evaporate more quickly, reducing the risk of landslides. According to Luca Ciabatta, hydrologist at the Research Institute of Geo-Hydrological Protection in Perugia, “this study is innovative in considering the impact of soil moisture on landslides, a factor that is often overlooked”.

Another unknown is how climate change will affect precipitation and soil in specific areas. “When considering risks caused by climate change, some uncertainty will always remain,” says Zappa. “But it’s crucial to evaluate what the worst-case scenario is, to inform risk assessments and plan adaptation strategies.”