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Vegetation cover affects the speed of snowmelt in tundra regions

04 April 2012 Finnish Meteorological Institute

Climate change has increased vegetation in Arctic tundra regions. According to a recent study, the increase in vegetation in tundra regions may further accelerate global warming.

The main objective of the study conducted by the Finnish Meteorological Institute was to use satellite observations for determining how the amount of vegetation affects snowmelt and thereby terrestrial albedo in the Arctic tundra regions. Satellite observations were collected from snowmelt periods (March–June) in 1995–2011.

“The study revealed that vegetation was thicker in Norway. One reason is that reindeer grazing is more intensive in Finland. The findings also indicated that snow almost always melted earlier in Norway than in Finland,” says Research Scientist Juval Cohen of the Finnish Meteorological Institute. With the exception of the differences in vegetation, the other prevailing conditions, such as temperature, precipitation and solar radiation, were almost the same in both countries. The difference in the melting of snow between Finland and Norway affects the albedo on land. During the snowmelt period, the albedo was almost always higher in Finland.

“Reducing vegetation or retaining the bare tundra would postpone the melting of snow in spring. This, in turn, could possibly slow down global warming,” says Cohen interpreting the findings of the study.

Snow melts earlier in spring

Owing to global warming, snow melts earlier in spring than it did a few decades ago. The earlier melting of snow has a major impact on the reflectivity, or albedo, of land areas. The albedo on land contributes to Earth’s energy balance, since it determines the ratio between solar radiation reflected by surfaces and radiation absorbed by surfaces. Snow has a considerably higher albedo than bare ground because snow is bright and reflects most of the incoming sunlight back into space. In contrast, snow-free ground is much darker and absorbs most of the incoming solar energy.

Global warming has also moved the tree line towards the north and has increased vegetation in Arctic tundra regions because plants can now survive in places that would have been too cold before. Reindeer husbandry also affects vegetation growth in the tundra regions of Lapland. More intense reindeer grazing reduces vegetation on the ground because the reindeer both eat and trample the plants. In some areas, the differences in vegetation on the two sides of fences separating grazing grounds are so great that they are clearly visible in satellite images.

The study calculated the difference in the solar energy absorbed in Finland and in Norway during the snowmelt period, in order to obtain a better idea of the impact of albedo on Earth’s energy balance. According to the calculations, the amount of solar radiation absorbed in Norway was greater than in Finland, owing to a lower albedo.

“In April and May in Norway, an area of 100 x 100 kilometres absorbs about 100,000 terajoules more solar radiation than a corresponding area in Finland. This is enough energy to melt an ice cube roughly 330 x 1,000 x 1,000 metres in size.

http://www.ncoetundra.utu.fi/

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