Long dry spells are already having an impact on agriculture and forestry, as well as shipping and other industries. Due to the decreases in summer precipitation, and because evaporation is increasing due to climate change, the problem of drought in summer will continue to become more pressing in the future. In the driest areas of Switzerland, snow and glacier melt are important water sources. The receding of the glaciers and expected snow deficits will place additional challenges on these areas in the future.
Mountains and valleys not only play a major role in determining temperature, they are also central to the distribution of precipitation. With an average annual precipitation of 543 mm in the 1991-2020 period, the driest place in the MeteoSwiss observation network is Stalden-Ackersand in the dry Visper valley in the canton of Valais. This is around half the amount of precipitation that falls in a year in central Switzerland. The longest uninterrupted dry phase was recorded in Lugano in 1988, with 77 consecutive days without precipitation.
Switzerland is in a moderate climate zone, and much longer dry periods have been recorded in other parts of the world. In the Chilean city of Arica, there were 172 months without precipitation between the years 1903 and 1918.
The wettest place in the MeteoSwiss observation network is Säntis, which sees 2,840 mm of precipitation in an average year. When a large amount of water falls from the sky in a short space of time, this increases the risk for landslides and flooding in a local area. The largest amounts of precipitation falling within a short space of time are normally seen in Ticino, where the southern orographic effect is responsible for large amounts of precipitation. In central Switzerland, heavy precipitation is mainly caused by thunderstorms. For this reason, the heaviest downpours occur primarily in the summer months.
Because warmer air can retain more water, climate change is contributing to the fact that heavy precipitation events are increasing. Records are one-off events, however. This is true for all weather parameters, but particularly for precipitation. A record-breaking weather event needs various factors to come together (including the weather situation at the time of the occurrence, the region of Switzerland in question, and the changes in weather over several days or weeks preceding the event). This is why some of the record precipitation events happened a long way back in the 20th century, in spite of climate change.
The table below provides an overview of record precipitation values in Switzerland, and compares them to records seen in the rest of the world.