Climate sensitivity of snow cover duration in Austria

The number of days with snow cover at Austrian climate stations, normalized by the maximum possible snow days within a season, is denoted n. This seasonal relative snow cover duration is considered a function of station height H and of the seasonal mean temperature T over Europe. When T increases, n decreases and vice versa. The function becomes saturated both for high stations at low European temperature (‘always snow’, n=1) and for low stations at high temperature (‘never snow’, n=0). In the saturated regions, the sensitivity s≡∂n(H, T)/∂T is practically zero, while in the transition region, s is extreme. The observed interannual fluctuations of T are considered here as simulation of a possible climate shift. s is determined for the climate stations of Austria from its snow cover record [1961–1990, 84 stations between 153 and 3105 m above sea level (a.s.1.)] by fitting the data of n for each individual station (local mode) as well as for all Austrian stations (global mode) with a hyperbolic tangent function. In the global mode, s reaches an extreme value of −0.34±0.04 K−1 in winter and −0.46±0.13 K−1 in spring. The implications of these results are discussed. Included in this discussion is the fact that a rise in the European temperature by 1 K may reduce the length of the snow cover period in the Austrian Alps by about 4 weeks in winter and 6 weeks in spring. However, these extreme values apply only to the height of maximum sensitivity (575 m in winter, 1373 m in spring); the actual sensitivity of individual stations located at higher or lower levels is less.