Given that only 10 percent of forest fires have a natural cause (lightning), it can be assumed that 90 percent of such fires are caused by inappropriate human behaviour (discarding glowing cigarette butts, barbecue fires that are not completely extinguished etc.). 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.