If hot summers like 2026 become normal, will Switzerland lose its water reservoir?

Lake Constance is more than a metre below its average summer level, and the water has reached about 27 degrees Celsius. That is roughly seven degrees above normal for late June. The lake has never had so little water in summer, according to the report.

The missing water points to a problem high in the Alps. Snow and glaciers act as Switzerland’s summer water reserve, feeding rivers and lakes after temperatures rise. Around half of Lake Constance’s water comes from melted snow, much of it through the Alpine Rhine, whose catchment area lies mainly in the canton of Graubünden.

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This winter, the snow reserve was not enough.

Normally, little water flows through the Alpine Rhine in autumn and winter because precipitation remains stored as snow. In May and June, melting snow increases the river’s flow. That meltwater helps offset the large amount of water that evaporates from Lake Constance during summer. It also keeps rivers cooler because snowmelt is cold.

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Then came the lack of precipitation over a very long period. Now, with these high temperatures and high evaporation, the drought is worsening further.

“This winter, the snow reserve was not enough,” Tobias Wechsler says. Long periods without precipitation then combined with high temperatures and high evaporation, worsening the drought. The summer of 2026 ranked among the hottest and driest since measurements began in 1864, with at least four heatwaves crossing Switzerland.

Researchers say such summers could become normal by the end of the century if current climate-protection measures remain in place. “This would accordingly be a normal day in 2099, but the extreme days could become even more extreme,” Wechsler says. Switzerland has already warmed by about three degrees Celsius since the pre-industrial period, compared with roughly 1.4 degrees globally.

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This would accordingly be a normal day in 2099, but the extreme days could become even more extreme.