Effect of reindeer grazing on snowmelt, albedo and energy balance based on satellite data analyses

Surface albedo has a major influence on the energy balance of the Earth. The albedo difference between snow-covered and snow-free tundra is high. Earlier studies have shown that taller and denser vegetation causes earlier snowmelt, and that shrub height and abundance, as well as the total biomass in summer reindeer pastures are lower than in winter pastures. Therefore, reindeer summer grazing could eventually delay the snowmelt and decrease the absorbed solar energy on the ground. The effect of reindeer summer grazing on the vegetation, snowmelt timing, surface albedo and ground heating is investigated in this study by comparing summer and non-summer pastures in the northern tundra areas of Fennoscandia. A comparison of vegetation types, NDVI, fractional snow cover and albedo between the Finnish year-round (including summer) pastures and the Norwegian non-summer (winter or spring/autumn) pastures is performed. Other factors influencing the snowmelt, such as surface air temperature, ground elevation and incoming solar radiation are taken into account. Information about the vegetation on the ground is based on a vegetation map compiled from Landsat TM/ETM + satellite data and ancillary map information. The NDVI, snowmelt and albedo analyses are performed using multi-temporal remote sensing data such as GlobSnow SE and MODIS based NDVI, snow and albedo products. The results here support previous studies and indicate that vegetation in the summer pastures is shorter and sparser and that snowmelt there occurs later than in the more densely vegetated, non-summer pastures. More shrubs protruding above the snowpack and earlier snowmelt on the Norwegian side lower the albedo during the snowmelt season. This causes higher solar energy absorption of up to 6 W/m2 in the snowmelt season and contributes up to 0.5 W/m2 to the yearly energy balance. Therefore this study suggests that summer reindeer herding can be used to delay snowmelt, increase surface albedo and to decrease the ground heating in the snowmelt season.