Evaporation components of a boreal forest: variations during the growing season

A Grelle, A Lundberg, A Lindroth, AS Morén… - Journal of …, 1997 - Elsevier
Journal of Hydrology, 1997Elsevier
To improve the understanding of interactions between the boreal forest and the climate
system as a key issue for global climate change, the water budget of a mixed pine and
spruce forest in central Sweden was estimated by measurements of the water flux
components and the total evaporation flux during the period 16 May–31 October 1995. Total
evaporation was measured using eddy correlation and the components were obtained using
measurements of precipitation, throughfall, tree transpiration, and forest floor evaporation …
To improve the understanding of interactions between the boreal forest and the climate system as a key issue for global climate change, the water budget of a mixed pine and spruce forest in central Sweden was estimated by measurements of the water flux components and the total evaporation flux during the period 16 May–31 October 1995. Total evaporation was measured using eddy correlation and the components were obtained using measurements of precipitation, throughfall, tree transpiration, and forest floor evaporation. On a daily basis, tree transpiration was the dominant evaporation component during the vegetation period. However, it could be efficiently blocked by a wet canopy associated with large interception evaporation. The accumulated total evaporation was 399mm, transpiration was 243mm, forest floor evaporation was 56mm and interception evaporation was 74mm. The accumulated sum of interception, transpiration, and floor evaporation was 51mm larger than the actual measured total evaporation. This difference was mainly attributed to the fact that transpiration was measured in a rather dense 50-year-old stand while total evaporation represented the average conditions of older, roughly 100-year-old stands. To compare eddy-correlation measurements with small-scale measurements of evaporation components, a source area analysis was made to select the flux data that give the best representation of the investigated stand. Especially under stable atmospheric conditions the requirements for surface homogeneity were very high and extreme care had to be taken to be aware of the flux source areas. Canopy water storage was determined by two methods: by the water balance of the canopy, which gave a result of 3.3mm; and by the so-called minimum method based on plots of throughfall versus precipitation, which gave a much lower value of 1.5mm. Seasonal interception evaporation constituted 30% of the precipitation.
Elsevier
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