Snow cover in the Alps has been melting almost three days earlier per decade since the 1960s. This trend is temperature related and cannot be offset by heavier snowfall. By the end of the century, the snow cover at 2,500 meters could disappear a month earlier than today, as simulations by environmental scientists at the University of Basel demonstrate.
Global warming requires huge adjustments in tourism, hydropower generation and agriculture in alpine areas. But the flora and fauna must also adapt to rising temperatures. By the end of the century, continuous snow cover for 30 days below 1,600 meters is expected to be a rare occurrence. “The snow cover protects alpine plants from frost and the growing season begins after the snow melts. Changes in snowmelt have a very strong influence on this period, ”explains Dr. Maria Vorkauf from the Department of Environmental Sciences at the University of Basel. She did intensive research on the physiology of alpine plants for her doctoral thesis.
New measurements at high altitude
In a new study, Vorkauf and his colleagues at the University of Basel and the Institute for Snow and Avalanche Research examined how the date of snowmelt has changed in recent decades and what changes may be expected by the end of the 21st century. For a long time, only a few sets of high altitude snow cover measurements were available, as measurements were usually only made near inhabited areas within 2000 meters. This changed with the IMIS measurement network, which entered service in 2000. It automatically records snow depths between 2,000 and 3,000 meters every half hour. The researchers combined this data with series of measurements from 23 lower stations with manual measurements dating back to at least 1958.
Analysis of the data showed that between 1958 and 2019, snow cover between 1,000 and 2,500 meters melted on average 2.8 days earlier each decade. This change was not linear, but was particularly marked in the late 1980s and early 1990s. This corresponds to large increases in temperature during this period which have been verified by climate research.
Simulation of the Alpine future
On the basis of the measurements analyzed, the researchers developed a model making it possible to predict the future evolution 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 coherent climate protection measures, the date of snowmelt in the last third of the 21st century is likely to change. advance six days per decade. This means that at the end of the century, snowmelt at an altitude of 2,500 meters would occur about a month earlier than today.
Research has also shown that early snowmelt at high altitudes cannot be offset by higher precipitation in winter, as climate models predict for Switzerland. “As soon as the three-week moving average of daily air temperatures exceeds 5 ° C, the snow melts relatively quickly,” explains Vorkauf. “At high altitudes in particular, the temperature is much greater than the depth of the snow cover.”
Early flowering and higher risk of frost
In the future, early snowmelt could extend the growing season of alpine plants by about a third. As studies on other alpine plant species know, an earlier start to the growing season results in fewer flowers, less leaf growth, and a lower survival rate due to the higher risk of frost. “Some species like the alpine sedge, which is typical of alpine meadows, will grow and flower earlier due to early snowmelt,” says Vorkauf.
Although temperatures in alpine areas rise more rapidly, alpine plant species are not more strongly affected by climate change than those in other elevations. “The topography and exposure of the alpine terrain create very diverse micro-climates on a small scale. Inside these, plants can retreat for short distances at the same altitude, ”explains Vorkauf. As a result, alpine plant species do not have to “flee” to heights, as is often assumed.
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