This article is republished from The Conversation under a Creative Commons license.
Snow is a defining feature of mountain ranges, and of winter itself for much of the world. But beyond its scenic value, snow plays a vital role in mountain ecosystems, as well as a range of human socioeconomic activity, and it is one of the climatic elements most sensitive to global warming. In recent decades, its quantity, duration and behavior have all changed significantly.
Snow varies a lot, both in terms of where and when it appears. In the mountains of the Iberia peninsula, winters can be abundantly snowy, or have almost no snow at all.
But this variability is not uniform. Lower elevations and areas such as the eastern Pyrenees have more irregular snow cover because of their position in relation to Atlantic air flows—the western and northern mountain ranges act as a barrier, capturing most of the moisture and leaving drier conditions to the east. This phenomenon, known as rain shadow, can also be observed in other Spanish mountains such as the Sierra Nevada in Granada, Andalusia.
At the local level, terrain and wind also influence snow accumulation. Together, these factors cause spatial and temporal snowfall trends to vary greatly.
Less Snow in the Northern Hemisphere
Across the northern hemisphere, snow cover has declined rapidly since the 1980s, mainly because of rising temperatures linked to anthropogenic climate change. This has given rise to what is known as hydrological snow drought, which occurs when snow accumulation is insufficient or melting is too quick, resulting in a deficit compared to a particular historical period.
Even so, at high altitudes and higher latitudes, snow accumulation during the cold season depends more on precipitation than on temperature. In the mid-latitudes of the Mediterranean basin, precipitation varies greatly from one year—and even one decade—to the next, with no clear trends observed throughout different historical periods.
In the Pyrenees, at high altitudes (over 2,000m) where temperatures remain below freezing, recent trends (2000–2020) are neutral or slightly positive. However, longer periods (1958–2017) have shown an overall decrease in the number of days with snow on the ground and in average snow depth.
Furthermore, this mountain range has shown an increasingly early and intense melt, associated with an increase in the energy available to melt the snow. This has also been linked to more frequent anticyclones during spring. These periods of atmospheric stability favor the entry of warm air masses, increase radiation and sensible heat, and accelerate melting. They now occur at higher temperatures due to global warming.
The Pyrenees’ Future
Studies based on climate simulations all project a decrease in snowfall in the northern hemisphere, regardless of climate model and greenhouse gas emissions scenario.
In the Pyrenees, projections point to a general reduction in snowfall, especially at lower altitudes, where small increases in temperature determine whether precipitation falls as snow or rain.
Even so, snow will not disappear from this mountain range altogether, even by the end of the century. Projections for the end of the 21st century (2080–2100) project reductions in snowfall ranging from -9% in a moderate emissions scenario (between 2,500 and 3,000 m) and -29% in a high emissions scenario (between 1,000 and 1,500 m), compared to the historical climate period (1960–2006).
These changes will also affect the length of the snow season, the speed of melting, and runoff peaks (the water that flows over the surface). A 1°C increase could reduce seasonal snowfall at 1,500 m by up to 30 %.
Furthermore, other studies have linked increased temperatures caused by climate change to extreme snowfall events like Storm Filomena in 2021. This is because higher temperatures contribute to increased evaporation, meaning more moisture in the atmosphere. If the temperature is below zero, this falls as snow.
Impacts on the Climate and Ecosystems
Snow is vital for mountain areas. It acts as a natural hydrological regulator, storing water during the cold months and releasing it gradually in spring and summer. A decline in snow cover alters runoff peaks, affects the availability of water resources, and impacts hydroelectric production.
Snow also plays a fundamental role in the global climate due to its high albedo, meaning its ability to reflect large amounts of solar radiation. The loss of snow cover increases energy absorption at the surface, generating feedback loops that increase the temperature.
Changes in snow also influence mountain ecosystems, the phenology (biological cycles) of plants and the evolution of glaciers, which depend on persistent snow cover to delay the exposure of ice during the summer. In addition, the increase in episodes of rain on snow, favoured by higher temperatures, can trigger rapid flooding, such as that which occurred in the municipality of Vielha (Lleida, Catalonia) in 2013, with high economic costs.
In this context, climate change poses a structural challenge to natural and economic systems in mountain areas. Addressing this new scenario requires progress in adaptation and mitigation strategies that enable the proper management of water, land and mountain activities.
Josep Bonsoms, Postdoctoral researcher and professor, Universitat de Barcelona
This article is republished from The Conversation under a Creative Commons license. Read the original article.
