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Widespread drainage measures, which were carried out mainly in the period 1950-
1990 on Finnish mires, have had significant climatic consequences, part of them being
temporary, part permanent. The aim of this study was to prepare charts of these climatic
effects by combining three sources of knowledge: (I) the climatic effect of drainage (e, °C),
as given by (Solantie 1994, 1998) for a 100% mire area in the climatically most affecting
stage, (2) fresh grid-square statistics of the proportion of drained mires compared
with the total area, and (3) annual statistics of the proportion of drained mires in various
stages having characteristic climatic effects, compiled by the Finnish Forest Research
Institute. Three charts show the maximum cooling effect of peatland drainage in Finland
during the first 15 years after the drainage in the period 1973-1982, as drained
mires in such a stage of drainage were then most common. Two charts show the warming
effect after successful afforestation and canopy closure; the canopy acts as a radiation
shelter and a mixing generator for the air beneath. In the middle boreal natural
zone, that most heavily drained, the mean monthly minimum temperatures in the period
1973-1982 were reduced by 1.5°C and the yearly frost-free period was shortened by 17
days. As a result of successful afforestation, the annual minimum temperature in the
middle boreal zone will be raised by 2°C to 3°C by the year 2005.
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Solantie,
The Finnish Meteorological Institute, P.O. Box 503, FIN-00101 Helsinki, Finland
Sähköposti:
ei.tietoa@nn.oo
