From 29 June onwards, Switzerland's glaciers will have exhausted their snow reserves. Every litre of meltwater now causes them to lose mass - this is Glacier Loss Day. Between the extreme years of 2003 and 2022 alone, 200 square kilometres of ice - an area almost as large as the canton of Zug - have disappeared. This is reflected in the volume of meltwater, as analyses show: although ice loss was more severe in the summer of 2022 than in 2003, less water flowed off the glaciers.
In brief
- 29 June marks Glacier Loss Day, the day from which onwards the glaciers lose ice volume with every litre of meltwater.
- The pattern of glacier melt so far this year is similar to that in 2022 - the worst ever recorded in Switzerland.
- The loss of glacier area is already impacting the volume of water flowing from the glaciers during extreme years.
It has not been a good start of the year for Switzerland's glaciers, and things are getting even worse. In April, their snow cover was at record lows in some places or, at best, average for a few individual glaciers. In March, Saharan dust blew into Switzerland, and the country is currently sweltering under a heatwave. The result: the ice is melting at an extreme rate, and 29 June is already 'Glacier Loss Day' - the day from which all further melting begins to erode the glacier's mass. Any remaining snow on the glacier that could 'feed' it has already been offset by melting in the lower-lying areas, and every hot day directly reduces the ice volume.
In 2022, this day arrived a few days earlier, on 26 June. There had also been little snowfall in winter back then, and with three heatwaves, that year was the warmest in Switzerland (so far) since records began in 1864. Only during the heatwave of 2003 were summer temperatures higher. The glaciers melted more rapidly in 2022 than ever before, losing around six per cent of their mass over the course of the year. During the current heatwave, it seems as though 2026 is hot on its heels (see graph).
Extensive melting does have its benefits: water from the glaciers helps cushion falling water levels and rising water temperatures, as long as there is still sufficient glacier area remaining. In extreme years - that is, when meltwater is most needed - glacier retreat could, however, already be making itself felt. As researchers from the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) have shown, between June and August 2022, meltwater from glaciers contributed less to runoff in most of the catchment areas studied than it did during the same period in 2003 - even though the glaciers melted much more extensively in 2022.
"The decline in ice cover is already clearly noticeable," says Matthias Huss, glaciologist at ETH Zurich and the WSL. However, the reduction in meltwater between 2003 and 2022 remains an isolated case: "The melt rates, which have been extremely high every year since 2022 and have also been rising significantly in the multi-year average since 2003, are currently still masking this effect." This is why researchers are not yet observing a decline in meltwater. However, Huss warns that this will only be the case for a limited time - until the ice masses have shrunk so much that even extreme melt rates can no longer compensate for the loss of mass.
Reference
van Tiel M., Huss M., Zappa M., Jonas T., Farinotti D. (2026)
Hydrol. Earth Syst. Sci. 30(1), 23-43. doi: 10.5194/hess-30-23-2026
