Snow coverage

Description of the results

At higher altitudes (2000 to 3000 m and above 3000 m) the winter snow cover was almost stable during the study period, with more than 70% of the area being covered by snow. At lower altitudes (1000 to 2000 m, < 1000 m), however, there were noteable year-to-year variations and a slight trend towards decreasing snow cover over the last 20 years. Until now, the winter of 2016/17 was the winter with the lowest snow cover at these altitudes. The winter of 2022 was the winter with the second lowest (for altitudes below 1000 m) and the fourth lowest (for areas between 1000 and 2000 m) snow cover since 2022. 2022 was the year with the lowest snow cover for all areas below 2000 m since 2002, especially in spring (March to April) (see Fig. 2).

Low snow cover in winter leads to low snow runoff in late spring/early summer and can lead to water shortages in agriculture, tourism, industry and energy production.

Water scarcity was an important issue in northern Italy in 2022, as a combination of low snow cover, lack of precipitation and a very warm spring and summer with above-average temperatures have a major impact on water availability.

Figure 2 shows that the snow cover values in the period from October 2021 to March 2022 are below the long-term average and close to the lowest values observed in the period 2000 to 2021. The first quarter of 2022 is characterized by a lack of precipitation in the form of rain and snow across northern Italy. Changes in snow cover have a variety of impacts on Alpine flora and fauna, tourism, water availability for hydropower and agriculture.

European and international comparison

In general, snow cover has changed considerably in recent years (1) (2). Several recent studies have shown that the amount and duration of snow cover has decreased over the last 20 to 30 years, although there is considerable variation in the reference years and areas. The areas most affected are the Andes, parts of the Himalayas and the North American mountain ranges. Over the years, in the Alps, the decline in snow cover extent and duration has not been constant. In analyses based on ground-based snow depth data, the average trend from November to May is -8.4% per decade (1971 to 2019), while snow duration is decreasing by -5.6% per decade (3).

Method

The graph is derived from daily MODIS satellite images. The images were processed using an algorithm developed by Eurac Research (4) to determine the snow cover. The algorithm was developed taking into account the specificities of mountainous areas (topography and heterogeneity of cover) and using MODIS data at 250 m resolution. The result is a product with a better resolution than the MODIS MOD10 product developed by NASA (500 m). From these daily images, average values of snow cover in South Tyrol were calculated, with interpolation to compensate for missing information due to frequent cloud cover. These daily averages were then used to calculate the annual averages and the respective minimum and maximum values. It is important to note that although the MODIS satellite only provides information for the last 20 years and therefore long-term trends cannot be assessed, these data are a very important source of information as they provide the highest possible ground resolution, which is essential for understanding variations, especially in mountainous areas.

Sectors affected

• Water management

• Agriculture

• Natural hazard

• Hydropower

• Tourism

Related indicators

References

(1) Beniston, M., Farinotti, D., Stoffel, M., Andreassen, L. M., Coppola, E., Eckert, N., Fantini, A., Giacona, F., Hauck, C., Huss, M., Huwald, H., Lehning, M., López-Moreno, J.-I., Magnusson, J., Marty, C., Morán-Tejéda, E., Morin, S., Naaim, M., Provenzale, A., Rabatel, A., Six, D., Stötter, J., Strasser, U., Terzago, S., and Vincent, C., 2018: The European mountain cryosphere: a review of its current state, trends, and future challenges, The Cryosphere 12, 759-794. https://doi.org/10.5194/tc-12-759-2018

(2) Notarnicola, C., 2020: Hotspots of snow cover changes in global mountain regions over 2000-2018. Rem. Sen. Environ. 243, 111781. https://doi.org/10.1016/j.rse.2020.111781

(3) Matiu, M., Crespi, A., Bertoldi, G., Carmagnola, C. M., Marty, C., Morin, S., Schöner, W., Cat Berro, D., Chiogna, G., De Gregorio, L., Kotlarski, S., Majone, B., Resch, G., Terzago, S., Valt, M., Beozzo, W., Cianfarra, P., Gouttevin, I., Marcolini, G., Notarnicola, C., Petitta, M., Scherrer, S. C., Strasser, U., Winkler, M., Zebisch, M., Cicogna, A., Cremonini, R., Debernardi, A., Faletto, M., Gaddo, M., Giovannini, L., Mercalli, L., Soubeyroux, J.-M., Sušnik, A., Trenti, A., Urbani, S., and Weilguni, V., 2021: Observed snow depth trends in the European Alps: 1971 to 2019, The Cryosphere, 15, 1343–1382. https://doi.org/10.5194/tc-15-1343-2021

(4) Notarnicola, C.; Duguay, M.; Moelg, N.; Schellenberger, T.; Tetzlaff, A.; Monsorno, R.; Costa, A.; Steurer, C.; Zebisch, M. Snow Cover Maps from MODIS Images at 250 m Resolution, Part 1: Algorithm Description. Remote Sens. 2013, 5, 110-126. doi:10.3390/rs5010110

Contact

Eurac Research: Alexander Jacob, Carlo Marin, Claudia Notarnicola, Valentina Premier, Bartolomeo Ventura, Institute for Earth Observation