ALBERT

Description: The southern mountainous taiga of eastern Siberia has a sparse larch canopy and an understory dominated by a thick moss layer. The physiology of moss is very different from that of other plants, as mosses lack roots and vascular systems and take up water directly. During May 2002, we conducted hydrological and meteorological measurements in the taiga of eastern Siberia to investigate the role of understory moss on water and energy balances within a leafless larch forest. We found that below-leafless canopy net all-wave radiation partitions into 39% latent heat flux and 39% sensible heat flux, while the mean daily Bowen ratio is about 1. Ground heat flux on the moss surface is also an important factor, as it comprises 22% of net all-wave radiation. Evaporation from moss beneath the leafless canopy was 24 mm during the 1-month observation period, representing 23% of the water flux into the larch forest. This finding implies that moss intercepted 23% of the water flux into the larch forest. In addition, evaporation from the moss understory during May 2002 comprised 22% of total evapotranspiration previously estimated above the canopy (April-October 2001). We conclude that moss is an important component of the water and energy balance in larch forests in the taiga region. Copyright © 2007 John Wiley & Sons, Ltd.

Description: For a larch forest site near Yakutsk, energy and water fluxes are estimated and their variations are investigated using a one-dimensional land surface model with daily routine data. The estimation period is 1986-2000, including the period before the start of tower observation (1997) on the left bank of the Lena River. The land surface model includes three submodels: vegetation, snow cover, and soil. The model can calculate water and energy fluxes above and within the forest if meteorological data over the forest are given as input. Data used in this study are Baseline Meteorological Data in Siberia (BMDS) Version 3. This set comprises daily data of main meteorological elements. The procedure is as follows: (1) preparation of equations between routine Yakutsk data and larch tower data; (2) estimation of past meteorological data over the taiga using those equations; and (3) estimation of fluxes using the one-dimensional model. The date of leaf-out start is parameterized with soil temperature and accumulated air temperature. It corresponds to the green-up time obtained from satellite normalized difference vegetation index (NDVI) data. Estimated monthly deviation of net radiation, Rn, is 10 Wm-2. Its maximum is 20 Wm-2. The monthly deviation of latent heat flux, LE, is less than 12 Wm-2. Its warm season average is less than 7 Wm-2. Although the magnitude of LE is almost zero in December and January, and several Wm-2 aside from these 2 months, the sensible heat flux, H, sometimes becomes negative during the cold season. The variation of evapotranspiration is considerably smaller than that of precipitation. The evapotranspiration (E) normalized by potential evaporation (Ep), E/Ep is 0.37-04 in the warm season; it tends to be large when leaf-out starts early. The amount of evapotranspiration in the warm season can be estimated from Ep within an error of 5 mm using this relationship. Copyright © 2007 John Wiley & Sons, Ltd.

Description: This study investigates the hydrometeorological effects of intercepted snow in an intensely cold region. Observation of meteorological and hydrological elements in severely cold conditions, such as those in Siberia, is very difficult. One such typical element is that of snow interception. Therefore, this study applies a land surface model, which includes a relatively simple interception model for snowfall, to a taiga forest in eastern Siberia that is dominated by deciduous larch. The simulation demonstrates that solid water storage in the canopy is present from October to March. The finding concurs with photographs of the study site. Intercepted snow and ice decrease rapidly in March because of sublimation. Evaporation is low (0.01-0.05 mm day-1) in midwinter because the air temperature is very low. The average ratio of interception evaporation to precipitation is 0.16 in winter (October-March), 0.03-0.09 in midwinter, and 0.57 in March. Net radiation roughly balances with the sensible heat flux in midwinter. The albedo is almost constant at 0.35 in midwinter. Frost is negligible on the canopy in these simulations. Copyright © 2007 John Wiley & Sons, Ltd.

Description: In order to better understand the water cycle over tundra, micro-meteorological observations were carried out over tundra near Tiksi, northeastern Siberia, and seasonal variations in the energy budget components were estimated for a period of 2 years. As an average for 1998 and 1999, net radiation was partitioned into a sensible heat flux of 25-30%, to a latent heat flux of 50-55%, and to a soil conductive heat flux of 15-25%. These ratios were changed by wind direction. The southwesterly winds were warm and dry, reducing sensible heat flux or changing its direction towards the ground surface, while northeasterly winds were cold, resulting in a sensible heat flux into the atmosphere from the tundra surface. Southwesterly winds were associated with cyclone intrusions into this area, and northeasterly winds were associated with anti-cyclones. More frequent intrusions of cyclones would decrease the sensible heat flux and increase the latent heat flux. Copyright © 2007 John Wiley & Sons, Ltd.

Description: We attempted to clarify the runoff characteristics of a permafrost watershed in the southern mountainous region of eastern Siberia using hydrological and meteorological data obtained by the State Hydrological Institute in Russia from 1976 to 1985. We analysed seasonal changes in the direct runoff ratio and recession gradient during the permafrost thawing period. Thawing depth began to increase from the beginning of May and continued to increase until the end of September, exceeding 150 cm. Annual precipitation and discharge were in the range 525-649 mm and 205-391 mm respectively. The sum of the annual evapotranspiration and changes in water storage ranged from 235 to 365 mm. The mean daily evapotranspiration in June, July, August and September was 1·5 min day-1, 1·7 mm day-1, 1·5 mm day-1, and 0·5 mm day-1 respectively. The direct runoff ratio was highest in June, decreasing from 0·8 in June to 0·2 in September. The recession gradient also decreased from June to September. Since the frozen soil functioned as an impermeable layer, the soil water storage capacity in the thawing part of the soil, the depth of which changed over time, controlled the runoff characteristics. Copyright © 2005 John Wiley & Sons, Ltd.

Description: 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 (1.0) 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 value 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 1.16 mm day-1, and the maximum rate, 2.9 mm day-1, occurred at the beginning of July. For the growing season from 1 June to 31 August, this rate was 1.5 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. Copyright © 2001 John Wiley & Sons, Ltd.