Forest fire risk usually occurs during and after winters with little snow, after long periods of dry weather and during summer heatwaves, and especially if such conditions coincide with strong winds (e.g. foehn). All these factors can severely dehydrate trees, shrubs and the forest floor.
Forest fires in Switzerland most often affect small areas. Besides the valleys that are regularly exposed to the foehn, the primarily endangered regions are Valais, Graubünden and Ticino. People are seldom endangered by forest fires because Swiss legislation prohibits the construction of housing in forests.
The forest fire risk indicates the probability of a forest fire occurring. It can be exacerbated e.g. by people engaging in leisure activities, so that action needs to be taken even if the danger of a forest fire is low.
Ground and surface fires are unlikely to occur. Tree crowns are not affected. A lightning strike is unlikely to cause a fire.
Speed of spread: Usually slow.
Ground and surface fires may occur. Tree crowns are unlikely to be affected. A lightning strike may cause a fire.
Speed of spread: Slow to medium.
Ground and surface fires may occur. Individual tree crowns may also be affected. Lightning strikes are likely to cause a fire.
Speed of spread: Rapid in open terrain, medium in forest.
Hot surface fires spreading to individual tree crowns may occur. Burning embers may be thrown and spark new fires. Lightning strikes are highly likely to cause a fire.
Speed of spread: Rapid in open terrain and in forest.
Very hot ground fires and widespread crown fires may occur. Burning embers may be thrown over large distances and spark new fires. Lightning strikes are highly likely to cause a fire.
Speed of spread: Very rapid over long periods in open terrain and in forest.