The Research Of Model Of Forest Soil Evaporation Based On Canopy Structure

Soil evaporation is the important expenditure of forests water balance. It occupies an important position in the research of forest water balance. Beginnings with factors of impacting on forest soil evaporation, this paper research the relationship between soil evaporation and canopy structure and find their mathematical relationship. Finally, we can obtain the forest soil evaporation model through deducing the relationship. The purpose of this research is avoiding the complex physical nature of soil evaporation to explore a mathematic model of forest soil evaporation. Using this model, we can obtain soil evaporation from canopy structure. The main research findings are as follows:1. Among the microclimate factors, the order of the ability of effect on soil evaporation is as follows: Forest air temperature > Forest air humidity > Forest wind speed > Forest illumination strength. The correlation index between forest air temperature humidity and soil evaporation are 0.91 and 0.86. This reaches a very significant degree. The same as forest wind speed, the relativity between forest illumination strength and soil evaporation is small. It hasn't reach a significant degree. Forest air temperature and soil evaporation are exponentially related. Forest air humidity and soil evaporation are linearly related. Correlation models are as follows: E=21.961e 0.0831T R2=0.8928 E—Soil evaporation(g);T—Forest air temperature(℃) E=21.394H-745.613 R2=0.8499 E—Soil evaporation(g);H—Forest air humidity(%)2. Forest soil water content and soil evaporation are linearly related. They reaches a very significant degree. Correlation model is as follows: E=41.837W-605.97 R2=0.8295 E—Soil evaporation(g);W—0-30cm soil water content(%)3. Canopy structure(canopy density, tree height, thickness of canopy) and forest air temperature and humidity have closely related. The following regression equations can be obtained by multiple regression analysis.The equation of forest air temperature(T), canopy density(X1), tree height(X2) and thickness of canopy(X3) is as follow: T=28.81-3.295X1-0.19X2-0.885X3 R2=0.896The equation of forest air humidity(H), canopy density(X1) and tree height(X2) is as follow: H=27.612+4.096X1+0.032X2 R2=0.9764. Integrating the above equations and introducing the atmospheric factors, the mathematical model that based on canopy structure and soil moisture status can be obtained. E- Soil evaporation(g);T- Forest air temperature(℃);T0-Daily average air temperature out fores(t℃);H- Forest air humidity(%);H0- Daily average air humidity out forest(%);W- 0-30cm soil water content(%);X1- canopy density;X2- tree height(m);X3- thickness of canopy(m)。—X—1-Average canopy structure of the area;—X—2-Average tree height of the area(m);—X—3-Average thickness of canopy of the area(m).