Climate Teleconnections Influencing Historical Variations, Trends, and Shifts in Snow Cover Days in Finland

Abstract

<p>Snow cover days (SCDs), the number of days with snow water equivalent (SWE) greater than a given threshold, play a vital role in the climate system, hydrological cycle, and sustainable development in cold regions. This study used long-term (1951–2022) simulated daily SWE time series based on a temperature-index snowmelt model at Kaisaniemi, Kajaani, and Sodankylä stations in the south, center, and north of Finland, respectively. Days with simulated SWE > 1 mm were defined as possible (PSCDs), > 2.5 mm as shallow (SSCDs), and > 7.5 mm as deep (DSCDs) snow cover days. The Mann-Kendall trend free pre-whitening (MK-TFPW) test to detect statistically significant (<em>p</em> < 0.05) trends and the sequential <em>t</em>-test analysis of regime shift (STARS) to determine possible transitions in annual PSCDs, SSCDs, and DSCDs in Finland were used. On average, annual PSCDs, SSCDs, and DSCDs were about 130, 125, and 114 days at Kaisaniemi; 187, 183, and 173 days at Kajaani; and 216, 212, and 204 days at Sodankylä, respectively. At all these three stations, annual PSCDs, SSCDs, and DSCDs showed statistically significant (<em>p</em> < 0.05) decreasing trends (ranging from 0.31 to 0.94 days year^-1) during the water years (September-August) 1951–2022. In Finland, 1988 was a negative shift point for annual PSCDs, SSCDs, and DSCDs, by about 18.8–22.4 days. Such variability, trends, and shifts in annual PSCDs, SSCDs, and DSCDs were mainly controlled by the effects of wintertime surface air temperature (SAT) and precipitation fluctuations in different phases of climate teleconnections on snowpack hydrological processes (SHPs). In both northern and southern Finland, accordingly, annual SCDs were most strongly influenced by the Arctic Oscillation (AO). In central parts, however, the East Atlantic/West Russia (EA/WR) was the only influential climate teleconnection for interannual variations in SCDs over time.</p>