Many specially adapted Alpine plants depend on the annual snows which blanket the mountain range as a form of insulation, but as snowmelt begins earlier each year due to the climate crisis, these plants are increasingly losing this protective layer, exposing them to deadly frosts, researchers say.
Snow cover in the European mountain range has been melting around three days earlier per decade since the 1960s.
By the end of this century, snow at 2,500 metres could be around for a month less than it is today, and continuous snow cover for 30 days a year below 1,600 metres is expected to be a rare occurrence.
“Snow cover protects alpine plants from frost and the growing season begins after the snowmelt,” said Dr Maria Vorkauf of the Department of Environmental Sciences at the University of Basel, who researched alpine plant physiology for her doctoral dissertation.
“Changes in the snowmelt have a very strong influence on this period,” she said.
Dr Vorkauf and colleagues at the University of Basel and the Institute for Snow and Avalanche Research investigated how the date of snowmelt has changed in recent decades and what shifts can be expected by the end of the 21st century.
They said that for a long time, only a few measurement series of snow cover at high elevations were available, as they were usually only made near inhabited regions below 2,000 metres.
This changed with the creation of a network of almost 200 measuring stations which went into operation in 2000.
The network automatically records the snow depth between 2,000 and 3,000 metres every half hour. The researchers combined this data with measurement series from 23 lower-lying stations with manual measurements going back to at least 1958.
The researchers’ analysis of the data revealed that between 1958 and 2019, snow cover between 1,000 and 2,500 metres melted an average of 2.8 days earlier every decade.
This shift was not linear, but was particularly strong in the late 1980s and early 1990s. This corresponds to strong temperature increases in this time period that have been verified by climate research.
The research team then developed a model which makes it possible to forecast the future development of alpine snow cover.
They combined their data with the latest climate scenarios for Switzerland. If greenhouse gas emissions continue to rise as they have so far, without consistent climate protection measures, the date of snowmelt in the last third of the 21st century is likely to move forward by six days per decade.
This means that by the end of the century, snowmelt at 2,500 metres elevation would occur about one month earlier than today.
The research also showed that the earlier snowmelt at high elevations cannot be compensated for by greater precipitation in the winter, as is predicted by climate models for Switzerland.
“As soon as the three-week running mean of daily air temperatures exceeds 5C, snow melts relatively quickly,” said Dr Vorkauf.
“At high elevations in particular, temperature is much more important than the depth of the snow cover.”
In the future, the early snowmelt could extend the growing season of alpine plants by about a third,” the research team’s models suggested.
For many alpine plant species, an earlier start to the growing season leads to fewer flowers, less leaf growth and a lower survival rate due to the higher risk of frost.
"Some species such as the Alpine sedge, which is typical of alpine grasslands, will grow and flower earlier because of the early snowmelt,” said Dr Vorkauf.
Although temperatures in alpine areas are rising faster, alpine plant species are not more strongly affected by climate change than those at other elevations.
“The topography and exposure of alpine terrain creates very diverse microclimates on a small scale. Within these, plants can retreat over short distances at the same elevation,” Dr Vorkauf said.
As a result, alpine plant species do not have to “flee” to the heights, as is often assumed.
The research is published in the journal Climatic Change.