Abstract
Abstract. Land cover changes can impact the climate by influencing the surface energy and water balance. Naturally treeless or sparsely treed peatlands were extensively drained to stimulate forest growth in Finland over the second half of 20th century. The aim of this study is to investigate the biogeophysical effects of peatland forestation on regional climate in Finland. Two sets of 18-year climate simulations were done with the regional climate model REMO by using land cover data based on pre-drainage (1920s) and post-drainage (2000s) Finnish national forest inventories. In the most intensive peatland forestation area, located in the middle west of Finland, the results show a warming in April of up to 0.43 K in monthly-averaged daily mean 2 m air temperature, whereas a slight cooling from May to October of less than 0.1 K in general is found. Consequently, snow clearance days over that area are advanced up to 5 days in the mean of 15 years. No clear signal is found for precipitation. Through analysing the simulated temperature and energy balance terms, as well as snow depth over five selected subregions, a positive feedback induced by peatland forestation is found between decreased surface albedo and increased surface air temperature in the snow-melting period. Our modelled results show good qualitative agreements with the observational data. In general, decreased surface albedo in the snow-melting period and increased evapotranspiration in the growing period are the most important biogeophysical aspects induced by peatland forestation that cause changes in climate. The results from this study can be further integrally analysed with biogeochemical effects of peatland forestation to provide background information for adapting future forest management to mitigate climate warming effects. Moreover, they provide insights about the impacts of projected forestation of tundra at high latitudes due to climate change.
Highlights
Climate response to anthropogenic land cover change happens more locally and occurs on a much shorter time scale compared to global warming due to increased greenhouse gases (GHG) (IPCC, 2013)
There are two regions in northern Finland that show opposite changes compared to the peatland forestation area in the middle west of Finland with cooling in the spring and warming in the growing season
An increase of less than 0.2 K is seen in T2 m in the southeast of Finland in July and August as well as in the very south of Finland throughout the growing season, which is mainly due to the change from mixed forest to coniferous forest and the increased artificial areas respectively
Summary
Climate response to anthropogenic land cover change happens more locally and occurs on a much shorter time scale compared to global warming due to increased greenhouse gases (GHG) (IPCC, 2013). For the climate impacts of past large-scale afforestation, studies show that the most obvious effects of the increase of forests in boreal areas are warming during snow-cover periods due to decreased surface albedo and cooling in summertime from increased evapotranspiration (ET) in tropical areas with sufficient soil moisture (Bala et al, 2007; Betts, 2000; Betts et al, 2007). In Finland, it is the dominant land cover change over the last half century due to the high fraction of pristine peatland and the need for timber production.
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