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“In the Pyrenees the snow used to last until May and now only until April”


Climate change in Pyrenees is causing the snowpack to melt about a month earlier, that the trees grow taller and are ‘thinning’ the permafrost, that is, the icy cover of the ground. One of the consequences will be a contribution of meltwater in periods other than the current one and the growth of forests at levels where there are none now.

How is global warming affecting the Pyrenees?

As it is a mountain area, the changes induced by global warming are observed in an accelerated manner or with a more marked increase. In the Pyrenees we can corroborate that the glaciers, although they are very small and have been reducing their thickness for 200 years, in the last 40 years this decrease has been more marked.

And what state is the snow cover in?

The thing with snow is that we have a lot of variability. One year there is a lot of snow and the next, very little. Therefore, it is very difficult to see the changes. What is happening is that the snow cover disappears sooner, it no longer lasts so many months. Some time ago, the snowy blanket could remain until the end of May in a very relevant extension; today this extension decreases much earlier, at the end of April.

Does this happen because it melts faster or because of the lack of precipitation in the form of snow?

If we talk about climate trends, we do not observe large changes in precipitation, but we do see changes in temperature. The temperature, especially in spring or summer, increases more markedly. In this way, although we accumulate similar amounts of snow, as higher temperatures occur earlier, the snow will disappear sooner. It would be more linked to the thermal increase than to a precipitation trend. There are years when it snows a lot and others when it snows little, but this also happened to us 50 years ago.

In the Alps, for example, although more precipitation is expected, less will occur in the form of snow. Is this expected to happen in the Pyrenees as well?

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Yes, that is what the climate change scenarios show us in relation to the Pyrenees. In the future, although the temperature in winter will not notice an increase as marked as in summer or spring, the snowfall will arrive later and end sooner. If we add to this that during the warm season it will be hotter, the result is that the snow cover will last less and, therefore, the mountain and high mountain pastures will have more time of exposure to solar radiation. and at temperature, therefore, they will be able to grow more.

In other high mountain areas, such as Mount Teide, what scientists clearly see is an increase in night temperatures. Do you see a similar trend?

In urban areas these tropical nights can be observed, but in mountain areas we find another peculiarity in order to study them and that is that while other places have climate records of up to 100 or 80 years, in mountain areas it is difficult to go beyond the 80s, and especially if we are at a higher altitude. Therefore, we cannot know very well if we are really having an increase in warm nights or in the global climate trend.

There are several impacts referred to for the ecosystem of the Pyrenees, can any of them be seen already?

In the Pyrenees what we see is that gradually in recent years the trees are colonizing higher areas. The bushes are reaching areas where before there were only grasses, because there is a better temperature and there is no snow; and in time they will give rise to a forest. That is a remarkable change for the ecosystem, because the forests also demand water. The forest mass will cause part of the precipitation not to revert to the river courses, but to the forest itself.

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Another impact highlighted by a recent study on the Alps in Switzerland is the loss of water supply in the future.

In the Ebro valley, for example, there is an increase in water between May and June because the snow is going to melt. By shortening the period in which we have available snow, perhaps it will melt in March or April, that means that the water that we had available for a warmer period of the year, we will have it much sooner. This is going to force us to learn to manage river channels with different characteristics.

“The bushes are reaching areas where before there were only grasses, because there is a better temperature and there is no snow; and with time they will give way to a forest”

Your research team has found evidence that there is also permafrost in the Pyrenees, what does it mean and what are the risks of melting?

Yes, in some areas of the Pyrenees there is permafrost (frozen ground) in the snowiest areas. Normally, the snow protects it from solar radiation and temperature increases, but if we have less snow, the permafrost will be exposed to the summer heat earlier and will gradually disappear.

And what consequences can it have?

In the Pyrenees its disappearance does not entail a consequence of great weight except for the people who may be in the vicinity. However, in other areas of the planet, such as Siberia, where permafrost forms all the soil, there is a destabilization of the land where there are areas with roads and buildings. Also in these areas, where permafrost occupies a significant area, gases can be released into the atmosphere. In our latitudes the worst consequence is the destabilization of certain walls. This, on a climbing route, can have safety issues and if there was someone climbing this wall, their life would be in danger.

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