Switzerland braces for second heatwave as drought deepens and water levels sink to record lows

Heatwave alert and expected temperatures

MétéoSuisse issued a level-3 heatwave warning on Monday for the Swiss Plateau from Geneva to Basel, the Three Lakes region, and Ticino. The alert runs at least until Monday 13 July. South of the Alps, high temperatures arrived over the weekend; Locarno broke its daily record for 5 July, reaching 34°C against the previous 33.6°C set in 1952.

North of the Alps, the heat builds from Tuesday, first in the northwest and then across the lowlands by Thursday. Maximums of 31–35°C are forecast, with the Basel region, Geneva, Valais, and the upper Aare valley likely to see 33–37°C on Thursday and Friday. Night-time lows will stay between 15°C and 23°C, warmer in cities where heat dissipates more slowly. Tropical nights are possible towards the weekend.

It won't be quite as hot as in June.

I currently do not expect the coming heatwave to reach the extent of the exceptional heatwave of late June and early July.

Drought and water shortages

Switzerland has been drying out for months. Over the past 90 days, precipitation on the northern side of the Alps and in Valais has been only about half the climatological average, according to the Federal Office for the Environment (Bafu). The agency’s drought index, which factors in two years of rain and snow, soil moisture, and river and lake levels, now classifies most areas as dry, very dry, or extremely dry.

Several rivers in the Jura, central, and western midlands are carrying less water than usual. Lake Constance is lower than ever recorded at this time of year. Levels in Lake Walen, Lake Zug, and Lake Sempach are also unusually low. Reservoirs stood at their second-lowest end-of-June level in a decade, and the situation for glaciers is described as catastrophic.

The drought will probably keep us quite busy.

Health and safety risks

MétéoSuisse warns of a significant risk of health problems and physical discomfort during a level-3 event. People are advised to drink at least 1.5 litres of unsweetened, non-alcoholic fluids per day and to avoid strenuous activity in the hottest hours. Neither people nor animals should be left in parked cars.

Forest fire danger is rising as soils dry further. The strong west wind expected in north-eastern Switzerland will accelerate evaporation. Small water bodies are already reaching bathtub temperatures, and fish die-offs cannot be ruled out. Agriculture urgently needs irrigation, especially for arable land.

Weather pattern and outlook

A stable high-pressure system centred over the near Atlantic is extending towards central and western Europe, locking in sunny, hot conditions. Meteorologists describe an Omega block, where the jetstream forms a horseshoe-shaped wave that traps the high between two lows, causing the weather to stall for days or even weeks.

The powerful anticyclone centred over the near Atlantic will gradually extend towards central and western Europe in the coming days, bringing a period of stable and hot weather across the whole country.

Thunderstorms are possible between Friday and Sunday, but they are expected to bring only temporary and localised relief. A widespread, soaking rain is not in the forecast. The end of the heatwave remains highly uncertain.