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Correlation Analysis of Water and Heat Fluxes with Environmental Variables over Lawn in Semi-arid Area

WANG Xiuxin~(1,2) LIU Xin~2 CHEN Shenghai~2 ZHU Qijiang~2 HU Yumei~2 (1. College of Computer Science and Information Technology, Guangxi Normal University, Gnilin 541004, China; 2. State key Laboratory of Remote Sensing Science,Beijing Key Laboratory for Remote Sensing of Environment and Digital Cities, School of Geography, Beijing Normal University, Beijing 100875, China)  
Lawn is the important part of green space.The green space project of Green Olympics was proposed by Beijing municipal government and got large amount of financial investment. However how the project to improve ecological environment needs to be evaluated quantitatively.So it is very significant for us to study water,heat fluxes over lawn quantitatively. The surface energy fluxes and the environmental variables were measured continuously with two eddy covariance systems over wild lawn and bare farmland in the suburb of Beijing on May 2005.Base on the measurements,the different surface fluxes were analyzed and compared in this paper.The influent weights of environmental variables for the fluxes were gotten with correlation analysis.The results show that most of incident solar radiation is changed into the energy in vegetable transpiration and soil evaporation for lawn.Latent heat flux is the major term in energy budget investigation for lawn.On the contrary,sensible heat flux is the dominant consumer of net radiation for bare soil.Latent heat flux occupies about half of net radiation energy over lawn and is about 20% greater than that over bare soil.According to surface energy balance,as latent heat flux consumes most of net radiation energy over lawn,sensible heat flux becomes about 30% less than that over bare soil,and the energy gotten by soil under grass is near a half less than that by bare soil.The ground temperature of lawn is lower than that of bare soil in the daytime,the maximum temperature difference between two surfaces reaches about ten centigrade at the same moment.The atmospheric temperature at the height of 1.5 meter over lawn is about one centigrade lower than that over bare soil.The relative humidity over lawn is about 5% higher than that over bare soil.The fluxes are significantly correlated with several environmental variables such as net radiation,ground temperature,atmospheric temperature,and relative humidity (that is only for latent heat flux).The most important environmental variable controlling the fluxes is net radiation.Then the environmental variable impacting the fluxes rank as follows:the difference between ground temperature and atmospheric temperature,ground temperature,relative humidity (that is only for latent heat) and atmospheric temperature.Wind speed has less influence on the fluxes.It is also showed that the ground temperature of lawn influences the fluxes much less than that of bare soil,and the difference between ground temperature and atmospheric temperature affect sensible heat flux much more than the ground temperature.
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