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 seas onal relative snow cover duration is considered a function of station heigh t 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 sta tions at low European temperature ('always snow', n = 1) and for low statio ns at high temperature ('never snow', n = 0). In the saturated regions, the sensitivity s = partial derivative n(H, T)partial derivative T is practica lly zero, while in the transition region, s is extreme. The observed intera nnual fluctuations of T are considered here as simulation of a possible cli mate shift. s is determined for the climate stations of Austria from its sn ow cover record [1961-1990, 84 stations between 153 and 3105 m above sea le vel (a.s.l.)] by fitting the data of n for each individual station (local m ode) as well as for all Austrian stations (global mode) with a hyperbolic t angent 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 discussio n 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 w inter and 6 weeks in spring. However, these extreme values apply only to th e height of maximum sensitivity (575 m in winter, 1373 m in spring); the ac tual sensitivity of individual stations Located at higher or lower levels i s less. Copyright (C) 2000 Royal Meteorological Society.