Influence of snow making on albedo and local radiative forcing in an alpine area

In the present paper, the climate cooling potential of technical snow making on ski slopes is investigated with regard to radiative forcing. It is well-known, that snow shows a higher degree of reflection compared to other ground surfaces. During snow-poor winters, guaranteeing snow covered ski slopes by using snow making may therefore lead to an increase in the albedo of a mountainous region. Since increasing albedo engenders a negative radiative forcing, the cooling potential of snow production on ski slopes is of particular relevance in the context of the current climate debate. Investigations were however generally performed for flat surfaces. Several studies nevertheless demonstrated that the topography leads to a substantial decrease in the mean albedo of a given region. This is attributable to shading effects and to slope inclinations. The present study was therefore dedicated to the accurate simulation of the impact of the albedo increase of ski slopes on the mean albedo and on the resulting change in shortwave radiative budget of a chosen mountainous region. We used therefore a state of the art 3-dimensional radiative transfer model. The investigations were carried out for the skiing area Saalbach-Hinterglemm in Austria. Broadband snow albedo values between 0.61 and 0.62 in cloudless conditions and 0.64 and 0.65 in cloudy conditions for solar zenith angle (sza) between 30 and 80 degrees were used for the simulations. An uncertainty of ?0.17 was taken into account. First a sensitivity study was performed, that showed a substantial decrease in the mean albedo of the ski slopes as a function of slope inclination. A strong impact of topography and of surrounding trees on the mean albedo of the ski slopes of up to 40% and 14% respectively was found at high sza under clear sky conditions. Compared to snow free conditions an increase in albedo between 0.18 and 0.36 was observed, the higher values for smaller sza and assuming no trees in the surroundings. Only related to the ski slopes a radiative forcing between -7 and -35 W/m2 was obtained. If the long-term snow cover conditions were taken into account, snow making lead to a change in albedo, only, in March and April. The increase in albedo was just below 0.10 in April and 0.02 in March, resulting in a radiative forcing around -12 W/m2 and around -1.5 W/m2 respectively. Though, in order to analyze an eventual cooling effect on climate the whole carbon footprint related to the production of technical snow making shall be determined.

Automated summary

This study investigates the climate cooling potential of technical snow making on ski slopes, showing that the high reflectivity of snow can reduce radiative forcing to a certain extent, which is relevant to the current climate debate. The impact of topography and surrounding environment on snow albedo is significant and should be taken into consideration. In long-term snow cover conditions, technical snow making only affects albedo in March and April.