Study Of Water Balance And Water Use Efficiency In The Loess Plateau Of China

The government introduced some of the reforestation project from 2000,such as the "Grain for Green Project".This study reveals the interactions of water balance and water use efficiency of different ecosystems using evapotranspiration,net primary productivity and climate variables(precipitation and temperature)under different tree cover combining with climatic date and remote sensing data to evaluate ecological effect of the afforestation and to analysis impact on the environment from 2000 to 2014.Results showed that(1)Tree cover experienced A significant rise(P<0.05),but nontree cover experienced fluctuation but a notably rise(P>0.05)in the past 15 years,2000~2014.Precipitation and temperature is a key factor led to the latitude zonal of tree cover,which increased from southwest to northeast.85% of area of tree cover are significant or not significantly increased in the Loess Plateau.Besides,the area of tree cover increased significantly with a significant reduction of nontree cover.(2)Precipitation increases from northwest to southeast.Temperature significantly correlation with altitude(P<0.05)and the mean Temperature is about 8.5℃ in the past 15 years.Tree cover was greater in rainy area than dry area,higher temperature area than lower temperature area when tree cover is low.But,the low temperature led to more tree cover than high temperature when tree cover is high.Lower of the coefficient of variation of precipitation led to more tree cover than higher.(3)Evapotranspiration and water balance experienced a notably rise(P>0.05)in the past 15 years(2000~2014)and precipitation is a key factor than temperature.Besides,evapotranspiration was greater in rainy area than dry area,higher temperature area than lower temperature area.Areas with higher or lower ratio are decreasing,while areas with medium ratio are expanding.The evapotranspiration increases with precipitation in different ecosystem except MH.(4)The climate and vegetation influence NPP and WUE.NPP increase area accounts is 88.9% in the total area on the Loess Plateau which increased significantly(P<0.01)from northwest to southeast.The NPP and WUE increases with tree cover in different ecosystem except FH.