Abstract
Abstract. Simulations by the EURO-CORDEX (European branch of the Coordinated Regional Climate Downscaling Experiment) regional climate models indicate a widespread future decrease in snow water equivalent (SWE) in northern Europe. This concurs with the negative interannual correlation between SWE and winter temperature in the southern parts of the domain but not with the positive correlation observed further north and over the Scandinavian mountains. To better understand these similarities and differences, interannual variations and projected future changes in SWE are attributed to anomalies or changes in three factors: total precipitation, the snowfall fraction of precipitation and the fraction of accumulated snowfall that remains on the ground (the snow-on-ground fraction). In areas with relatively mild winter climate, the latter two terms govern both the long-term change and interannual variability, resulting in less snow with higher temperatures. In colder areas, however, interannual SWE variability is dominated by variations in total precipitation. Since total precipitation is positively correlated with temperature, more snow tends to accumulate in milder winters. Still, even in these areas, SWE is projected to decrease in the future due to the reduced snowfall and snow-on-ground fractions in response to higher temperatures. Although winter total precipitation is projected to increase, its increase is smaller than would be expected from the interannual covariation of temperature and precipitation and is therefore insufficient to compensate the lower snowfall and snow-on-ground fractions. Furthermore, interannual SWE variability in northern Europe in the simulated warmer future climate is increasingly governed by variations in the snowfall and snow-on-ground fractions and less by variations in total precipitation.
Highlights
Due to its location near the western margin of the Eurasian continent, northern Europe experiences large interannual variations in winter climate associated with variations in the atmospheric circulation (Tuomenvirta et al, 2000; HansenBauer and Førland, 2000; Chen, 2000; Lehtonen, 2015; Saffioti et al, 2016; Räisänen, 2019)
Three main questions are explored. (i) Which factors control the interannual variability of snow amount in northern Europe? (ii) How do the dynamics of the interannual variability differ from those of the projected long-term climate change? (iii) And how does the projected climate change affect the dynamics of interannual variability?
In the Introduction, three main questions were posed. (i) Which factors control the interannual variability of snow amount in northern Europe? (ii) How do the dynamics of the interannual variability differ from those of the projected long-term climate change? (iii) And how does the long-term climate change affect the dynamics of interannual variability? The answers, based on the ERA5-Land reanalysis and the EURO-CORDEX regional climate models (RCMs) simulations, can be summarized as follows
Summary
Due to its location near the western margin of the Eurasian continent, northern Europe experiences large interannual variations in winter climate associated with variations in the atmospheric circulation (Tuomenvirta et al, 2000; HansenBauer and Førland, 2000; Chen, 2000; Lehtonen, 2015; Saffioti et al, 2016; Räisänen, 2019). Record-breaking positive anomalies of 3–5 ◦C in the November-to-March mean temperature extended from southern Sweden to southern and central Finland, the Baltic States and western Russia, whereas the precipitation surplus was unusually large especially in Finland. This contrast was confirmed by station measurements of snow depth. Sodankylä in central Finnish Lapland (S in Fig. 1) reached a snow depth of 127 cm on 15 April 2020, exceeding its previous record of 119 cm from April 2000
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