Water and Energy Exchanges at Forests and a Grassland in Eastern Siberia Evaluated Using a One-Dimensional Land Surface Model

Abstract

Water and energy exchanges are evaluated for two larch forests, one pine forest, and one grassland area in eastern Siberia near Yakutsk using a one-dimensional land surface model. Diurnal and seasonal variations of fluxes are simulated reasonably with general stomatal parameters at all sites. In the grassland site, the Bowen ratio is 0.2 in midsummer; it is smaller than that in forest sites (about 1). Sensitivity tests indicate that leaf area should be given accurately along with total plant area index including stem and branch areas. If both plant and leaf areas are given, the outline of seasonal heat balance can be simulated using the same stomatal parameters for forests and grassland sites with the model. In the larch site on the left bank of the Lena River, although input precipitation varies widely from 82 to 236 mm year to year from 1998 through 2000, calculated total evapotranspiration varies only within a range of 50 mm around 238 mm in the larch site. Understory evapotranspiration contributes 37%?44% to total evapotranspiration; interception is 15%?21% of precipitation. Evapotranspiration normalized by potential evaporation is 0.37 for larch sites almost independent of year; for grassland it is 0.52. At some sites, evapotranspiration in the warm season exceeds precipitation, thereby implying either a warm-season depletion of water storage in the soil column (most likely melted water from the thawing of the soil) or a horizontal transport of subsurface melt water from neighboring areas, or both.