Climatic changes have been observed since 1864, including a significant increase in temperatures and a rise in heat waves and heavy precipitation. These phenomena are occurring alongside an intensification of dry spells, particularly during the summer months. On the MeteoSwiss website, you will find comprehensive information on drought and dry spells in Switzerland. This page brings together various aspects of this topic.
Since measurements began, some of which date as far back as 1864, marked changes in a number of climate variables have been observed:
A warmer atmosphere can store more humidity, which makes for heavier precipitation. This does not necessarily mean an increase in total precipitation, though. In fact, there has been no significant change in total summer precipitation since measurements began. At the same time, the higher temperatures lead to increased evaporation, which is, in turn, conducive to drought.
Drought occurs when there is no precipitation for an extended period of time. Combined with hot days and high levels of evaporation, this dryness leads to drought in summer. This can put pressure on agriculture and forests.
Dry winters lack the snow and rain needed to fill the reservoirs for spring and summer, as well as presenting a challenge for snow sports.
There are various climate indices for drought. One commonly used indicator is the maximum number of consecutive dry days per year on which less than 1 mm of precipitation is measured. For other indicators, see “Drought indicators” below.
In Switzerland, an increase in drought can be seen for the period of 1981–2020, especially in the summer. This is due on the one hand to a slight decrease in precipitation and on the other hand to increased evaporation caused by climate warming in recent decades.
Without climate change mitigation, the average precipitation amount in the summer months will shrink, and evaporation will increase. The ground will become drier, there will be fewer rainy days, and the longest precipitation-free periods will last longer.
Drought is measured with the help of a number of different climate indices, including the Standardized Precipitation Evapotranspiration Index (SPEI), which looks at the water balance over a specific period of time. A negative SPEI signifies drier conditions in comparison to the long-term average, while a positive SPEI represents wetter conditions. If the SPEI value goes below -2, this means it is “extremely dry”, and with a value of above +2, it is “extremely wet”.
Evapotranspiration – the combination of evaporation and transpiration in plants – plays a central role in the occurrence of drought. Explanations of this and its influence on drought can be found on the page “Drought indicators”.
These publications contain detailed analyses and annual summaries of climate and weather phenomena, including drought.