Fens and bogs represent a considerable part of the boreal forest area of Scandinavia, but have not received much attention. To understand their role in the water and energy balances an investigation was carried out during the spring and summer of 1994 as a part of the NOPEX program. Groundwater level, precipitation and energy budget parameters were measured at the Ryggmossen bog, 35 km Northwest of Uppsala. The evaporation (10 min averages) was determined by the Energy Balance Bowen Ratio method and a reference evaporation (10 min averages) was also calculated according to Penman (1948). The results of the evaporation and energy balance study showed that the actual evaporation was 60% of the reference evaporation and that the evaporation rate was dependent on the groundwater depth. The weather during the period was warm with extremely low precipitation. The evaporation therefore decreased during the summer in response to the increased depth to the groundwater table. A relation was found between the groundwater level recession rate and the evaporation rate. The albedo increased during the summer and any occasional decrease could be attributed to individual rain storms.

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