The Effects Of Grain To Green Program On Regional Air Temperature In Northern Shaanxi Loess Plateau

Vegetation is an important component of terrestrial ecosystem,which plays an essential role in linking soil,atmosphere and hydrology.Between land and atmosphere,surface vegetation can,through biophysical and biochemical pathways,which makes it capable to impact the regional climate.In Northern Shaanxi Loess Plateau,irrational removal of nature vegetation by human activities caused severe soil erosion and deteriorated the local ecological environment.In order to restore the disturbed ecosystem,the Chinese government launched "Grain to Green" Program(GTGP).Under the implementation of GTGP,the ecological environment has exhibited significant improvement Therefore,it is necessary to identify the degree of climate change and evaluate the effect of the vegetation recovery on it,which could provide valuable reference to the studies of environment recovery and regional climate variation.Based on the content aforementioned,we used the land use data of 2000 and 2015,vegetation coverage,leaf area index and surface albedo in growing season in 2000-2015,based on the Weather Research and Forecast(WRF)model,to examine the trend of local temperature change and identify the interaction between temperature and vegetation variation.The main conclusions draw from this study including:(1)Between 2000 and 2015,the land cover patterns of Northern Shaanxi Loess Plateau changed remarkably.More than 3663.48 km2 croplands changed to grassland and woodland.Grassland and woodland increased by 2.56% and1.43%,respectively.Vegetation coverage and leaf area index in growing season increased significantly after the implementation of GTGP,increased by 1.37%/a(P<0.001),0.041/a(P<0.001),while the Albedo decreasing by-0.002/a(P<0.001).The change area mainly concentrated on the middle and southern part of the study area.(2)Before the implementation of GTGP,temperature in growing season kept significantly increasing in 1980-1999,as increased by 0.074 ℃ /a(P<0.01).After the implementation of GTGP,temperature stayed in a decrease trend in 2000-2015,with the decrease rate of-0.06 ℃ /a(P=0.025),especially in Yan’an,Shenmu and Yanchang meteorological stations.(3)Based on the WRF model,the impacts of land use and land cover change by GTGP on regional temperature were assessed.The WRF simulation results showed that differences in land use and land cover change patterns led to widespread reduction of temperature in growing season,average temperature decreased 0.078℃,especially in Yan’an,Shenmu and Yanchang meteorlogical stations(decreasing by 0.32 0.20 and 0.12℃,respectively).As indicated by the simulation results of WRF,we observed that the implementation of GTGP resulted in the increase of vegetation coverage,which led to the decrease of sensible heat flux and the increase of Latent heat flux,further took influences on the temperature variation in the study area jointly.