Semi-arid Underlying Surface To Air Interaction

Based on three years(2003～2005) of the eddy covariance (EC) observation over the semi-arid area (44°25′N, 122°52′E, 184m a.s.l) in Tongyu, Northeast China over the degraded grassland and the cropland surface, the seasonal and diurnal variations of the exchange of the water,energy and CO2 flux have been investigated. Tongyu observational station is also one of the reference sites of the CEOP(Coordinated Enhanced Observing Period ).The main results are in the following:1. The rainfall was strongly influenced by the land cover in the semiarid area and had strong heterogeneity in growing season (from May to September), especially during the convective weather system in summer.2. The latent heat flux is larger over the cropland surface than that over degraded land surface in the growing season, while in the non-growing season, their difference is very few. The sensible heat flux is the main part of the available energy except that in the growing season in the semiarid area. In the growing season the latent heat flux has the same order with the sensible heat flux. The net radiation flux has seasonal variation, while in winter is less than the half of that in summer. The soil heat flux at the ground surface over the cropland surface is smaller than that over the degraded grassland surface in the growing season. The available energy over the cropland surface is larger than that over the degraded grassland surface in the growing season. The available energy over the cropland surface is larger than that over the degraded grassland surface in the growing season, while in the non-growing season there is very little difference.3. The soil volumetric water content is less than 15% in the surface layer 0-20cm ) in the non-growing season. In the growing season the soil volumetric water content has a good correlation with the rainfall. The soil volumetric water content has a rapid increase during the snowmelt period. The soil water content in the thin soil layer(at 0.05m,0.10m and 0.20m) clearly indicated the pronounced annual wet-dry cycle. 4. The CO2 flux is less than 0.2 mg m-2s-1 over two ecosystems except the growing season . during the growing season, the carbon dioxide flux over the cropland ecosystem is a little larger than that over the degraded grassland ecosystem.5. The land surface parameters, such as surface roughness , surface albedo and bulk transfer coefficient, are determined for the cropland and the degraded grassland. And their seasonal variations and differences between the two land surface are also given.6. The results of water balance over the two land surface show that the water deficit over the cropland is obvious.