Time series of monthly snow making days for 20 weather stations in Germany and Austria, colour coded by increasing altitude, 21 year running mean (centred moving average). In October, there is a clear decrease in snow making days at the two highest stations, starting around 1960. This decrease is present in November and December at the second highest station, while it is less evident at the highest station. The lower stations remain at a roughly constant level, although some appear to show a downward trend in the later years of the time series. None of the stations show pronounced changes before 1960. Graphic: Hartl, et al., 2018 / Global and Planetary Change

ABSTRACT: Ski resorts increasingly rely on snow making to ensure good quality skiing regardless of the variability of the natural snow cover. This study aims to quantify past changes in snow making conditions based on an analysis of long-term wet bulb temperature time series from 20 weather stations in Germany and Austria. The weather stations are located at a range of altitudes from 267 m to 3109 m, in the vicinity of ski resorts. The lengths of the time-series range from 54 to 83 years. Using a threshold mean daily wet bulb temperature of −2 °C we define ‘potential snow making days’ and track changes in the number of snow making days in the months of the early skiing season (October, November, December) by computing linear trends, comparing consecutive 20 year periods, and Mann-Kendall trend testing of overlapping sub-periods. The number of snow making days changes least in October and most in December when averaged over all stations. Very high stations show more change in October and less change in December than the lower stations. Several stations show a significant decrease of snow making days per month, particularly in more recent sub-periods, but trends vary strongly between stations and for different sub-periods. Sub-periods with positive trends are present in earlier phases of the time series at some stations and inter-annual variability is generally 1–2 orders of magnitude greater than detected trends. Detailed microclimatic studies are necessary to determine potential future effects of changes in snow making conditions on the scale of a ski resort.

Analysis of past changes in wet bulb temperature in relation to snow making conditions based on long term observations Austria and Germany