Flux variation in a Siberian taiga forest near Yakutsk estimated by a one-dimensional model with routine data, 1986-2000

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, R_n, 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 (E_p), E/E_p 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 E_p within an error of 5 mm using this relationship.