The pre-melt season albedo and melt season timing of the Northern Hemisphere land areas have changed from 1982 to 2015
The albedo of the Northern Hemisphere land areas seasonally covered by snow have a significant effect on the global climate. Snow covered surface are brighter than other types of surface, such as vegetation or water bodies. It reflects most of the incoming solar radiation back to the atmosphere. Seasonal snow cover is very sensitive to environmental changes. The changes in snow covered area, duration of snow cover and snow surface reflective properties have a direct impact on the Earth's energy budget and thus, climate.
This study investigates the changes in the albedo of areas between 40°N and 80°N prior to melt season from 1982 to 2015. It also investigates the changes in the timing of the melt season. The study is based on optical satellite data. The albedo prior to melt season affects the melt season length and the melt processes during the melt period. It also indicates changes in the albedo during mid-winter.
The results show that the level of albedo has changed already prior to melt season and these significant changes concentrate to the areas of boreal forest zone. The pre melt albedo of the tundra areas remain unchanged. The direction of change depends on the area. The timing of the melt season has also changed in large areas, with spatial variability in the direction and magnitude of the change. The changes in melt season timing can be explained by changes in climate, most significantly the changes in air temperature.
The trends in pre melt season albedo. The red areas show increasing trends in albedo, that is, the surface is getting brighter. In the blue areas the surface is getting darker.
As a result of this study, a large dataset on melt season parameters was created. These datasets as well as the other results can be used to improve the modelling of climate in the areas covered by seasonal snow. The datasets have risen international attention and the data is planned to be used in different projects in several institutes around the world.
This work is part of the PhD work for a thesis which will be defended in 26 April 2019 at the University of Helsinki.
Further information:
researcher Kati Anttila, Finnish Meteorological Institute, tel. +358 50 441 2298, kati.anttila@fmi.fi
Anttila et al. 2018: The Role of Climate and Land Use in the Changes in Surface Albedo Prior to Snow Melt and the Timing of Melt Season of Seasonal Snow in Northern Land Areas of 40°N–80°N during 1982–2015. Remote Sensing, 10(10), 1619, https://doi.org/10.3390/rs10101619