MODIS (2001-2022) snow cover variability over Italy: a focus on the Alps and Apennines chain

Snow cover plays an essential role in regulating the Earth’s climate and it has significant impacts on human well-being in several parts of the world. In this study, the distribution of snow cover variables over the whole Italian territory, which includes the southern part of the Alps and the Apennines chain, are analysed between 2000 and 2022 using MODIS data acquired from Terra and Aqua platforms. In particular, after a pre-processing of the data, the start (SOS), the length (LOS) and the end (EOS) of the snow season have been calculated. As expected, the LOS shows the highest mean values over the Alps with an average equal to about 90 days for elevations above 500 m a.s.l. Conversely, the lowest values are seen over the Po Plain area with about 5 days for elevations lower than 500 m a.s.l. Moving to the south, the Apennine region shows higher values again for higher elevations with a mean value equal to 6 days in the West region and to 10 days in the East region. A clear dependence of LOS from elevation is evident, even if the large spread of the obtained values for each elevation underlines how also the dependence from other variables (e.g. slope, aspect, latitude and longitude) should be taken into account. 

The LOS series at the Italian scale shows a significant negative trend (between -5.1 days per decade and -0.6 days per decade, p-value ≤ 0.1) at elevations higher than 3500 m a.s.l. especially due to the signal observed over the Alps. Conversely, for elevations lower than 3500 m a.s.l., the trend is negative and significant only in the Apennines east region (between 500 m a.s.l. and 1500 m a.s.l.) with values between -9.9 and -6.2 days per decade (p-value ≤ 0.05).