Effects of climate change on evapotranspiration and soil water availability in Norway spruce forests in southern Finland: An ecosystem model based approach

Norway spruce (Picea abies) is sensitive to decreases in soil water availability. In this study, we simulated how the climate change may influence the hydrological processes with impacts on the growth of Norway spruce in three sites located in southern Finland (61^oN). The sites differed from each other in regard to the climate and soil water conditions; however, the initial structure of the tree stands was similar. Under the current climate, the canopy surface evaporation (E_c) increased, whereas the transpiration (E_t) remained at a constant rate over the simulation period, as the seedlings in the initial stand grew to full maturity. Under the changing climate, on average, the cumulative of E_c and E_g (evaporation from soil surface) were 16% and 14% higher than those under the current climate, respectively, whereas the cumulative E_t was 12% lower. The leaf area index (L) increased constantly on the sites with high (S_H) and medium (S_M) soil moisture, unlike on the site with low (S_L) soil moisture. The canopy conductance (g_cs) declined rapidly and earlier on the site S_L, which implied the acclimation of stomatal behaviour to drought. The increasing water loss through evaporation decreased the water infiltration into the soil profile, resulting in an increasing soil water deficit (W_d), especially on the site S_L. It also occurred earlier in all three sites under the changing climate. It was predicted that climate change will create a suboptimal environment for Norway spruce in southern Finland, particularly on the upland sites with lower groundwater table.