Abstract:The water and energy exchanges in forests form one of the most important hydro-meteorological systems. There have been far fewer investigations of the water and heat exchange in high latitude forests than of those in warm, humid regions. There have been few observations of this system in Siberia for an entire growing season, including the snowmelt and leaf-fall seasons. In this study, the characteristics of the energy and water budgets in an eastern Siberian larch forest were investigated from the snowmelt season to the leaf-fall season. The latent heat flux was strongly affected by the transpiration activity of the larch trees and increased quickly as the larch stand began to foliate. The sensible heat dropped at that time, although the net all-wave radiation increased. Consequently, the seasonal variation in the Bowen ratio was clearly 'U'-shaped, and the minimum value (1Ð0) occurred in June and July. The Bowen ratio was very high (10-25) in early spring, just before leaf opening. The canopy resistance for a big leaf model far exceeded the aerodynamic resistance and fluctuated over a much wider range. The canopy resistance was strongly restricted by the saturation deficit, and its minimum value was 100 s m 1 (10 mm s 1 in conductance). This minimum canopy resistance is higher than values obtained for forests in warm, humid regions, but is similar to those measured in other boreal conifer forests. It has been suggested that the senescence of leaves also affects the canopy resistance, which was higher in the leaf-fall season than in the foliated season. The mean evapotranspiration rate from 21 April 1998 to 7 September 1998 was 1Ð16 mm day 1 , and the maximum rate, 2Ð9 mm day 1 , occurred at the beginning of July. For the growing season from 1 June to 31 August, this rate was 1Ð5 mm day 1 . The total evapotranspiration from the forest (151 mm) exceeded the amount of precipitation (106 mm) and was equal to 73% of the total water input (211 mm), including the snow water equivalent. The understory evapotranspiration reached 35% of the total evapotranspiration, and the interception evaporation was 15% of the gross precipitation. The understory evapotranspiration was high and the interception evaporation was low because the canopy was sparse and the leaf area index was low.

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Marked increases in active‐layer and upper permafrost temperatures occurred in the central Lena River basin in association with abrupt increases in active‐layer soil moisture following the summer of 2005. The positive trend in soil temperature‐moisture relations was observed at monitoring sites in the Yakutsk area, regardless of vegetation and soil type. The increase in soil temperature appears to have started in response to the large amounts of snow that accumulated in the winter of 2004. Abnormally high pre‐winter rainfall and snowfall in the following three years accelerated soil warming through the effects of greater latent heat of freezing and insulation from atmospheric cooling in winter. The consecutive positive anomalies of snow depth and rainfall, which occurred widely in the central and southern Lena River basin during this three‐year period, increased soil moisture and appear to have altered the active‐layer thermal properties, which likely induced widespread warming of the surface layer of permafrost in this region. Copyright © 2009 John Wiley & Sons, Ltd.

Abstract:Soil moisture and its isotopic composition were observed at Spasskaya Pad experimental forest near Yakutsk, Russia, during summer in 1998Russia, during summer in , 1999Russia, during summer in , and 2000. The amount of soil water (plus ice) was estimated from volumetric soil water content obtained with time domain reflectometry. Soil moisture and its υ 18 O showed large interannual variation depending on the amount of summer rainfall. The soil water υ 18 O decreased with soil moisture during a dry summer (1998), indicating that ice meltwater from a deeper soil layer was transported upward. On the other hand, during a wet summer (1999), the υ 18 O of soil water increased due to percolation of summer rain with high υ 18 O values. Infiltration after spring snowmelt can be traced down to 15 cm by the increase in the amount of soil water and decrease in the υ 18 O because of the low υ 18 O of deposited snow. About half of the snow water equivalent (about 50 mm) recharged the surface soil. The pulse of the snow meltwater was, however, less important than the amount of summer rainfall for intra-annual variation of soil moisture.Excess water at the time just before soil freezing, which is controlled by the amount of summer rainfall, was stored as ice during winter. This water storage stabilizes the rate of evapotranspiration. Soil water stored in the upper part of the active layer (surface to about 120 cm) can be a water source for transpiration in the following summer. On the other hand, once water was stored in the lower part of the active layer (deeper than about 120 cm), it would not be used by plants in the following summer, because the lower part of the active layer thaws in late summer after the plant growing season is over.