Inter-annual and seasonal variations of energy and water vapour fluxes above a tropical seasonal rain forest in Xishuangbanna, SW China
西双版纳热带季节雨林水热通量

The values and variation characteristics of energy components,the relation of these energy components with net radiation and the characteristics of water balance in the forest were analyzed,based on the observation data of energy fluxes,meteorological parameters and biomass in a tropical seasonal rain forest in Xishuangbanna from January 2003 to December 2004.The results showed that annual net radiation was 3516.4 MJ/(m2 a)and 3516.6 MJ/(m2 a)in 2003 and 2004,respectively,of which 46% and 44% were used in latent heat flux,12% and 11% were lost as sensible heat flux.Annual mean canopy surface conductance was 10.3 mm/s and 10.0 mm/s in 2003 and 2004,respectively.Moreover,canopy surface conductance was lower in dry-hot season than those in fog-cool and rainy season.Canopy surface conductance correlated significantly and positively with leaf area index,but negatively with water vapour pressure deficit.In general,canopy surface conductance was not affected directly by soil water content,but highly depended on soil moisture status when soil water content was below 0.15 m3/m3.Annual total evapotranspiration was 663 mm and 634 mm in 2003 and 2004,respectively.Influenced by heavy fog and canopy surface conduction,the evapotranspiration of this forest ecosystem in dry season was lower than that in the rainy season,which was considered as one of the most important reasons that tropical seasonal rain forest could survive and flourish in Xishuangbanna at limit of water and heat.