Influence Of Vegetation Change On Climate In The Loess Plateau Under The Background Of Grain To Green Program

With the continuous warming of the global climate,people pay more and more attention to the regulation function of terrestrial ecosystems on the climate system,and vegetation management measures are considered to be an important means to alleviate climate warming.As the key link of the global carbon cycle,vegetation is the main source of material and energy,as well as an important link in the matten cycle and energy flow of the biosphere,and is the foundation of most of the earth ecosystems.The Loess Plateau is one of the areas where human activities have the most serious disturbance to the ecological environment.In 1999,China officially implemented the policy named GTG in the Loess Plateau region.This management measure is considered to be a large ecological restoration and rural planning project on a global scale..The policy of returning farmland to forests aims to restore the weak ecosystems in western China and reduce the serious consequences of a series of natural disasters such as drought,sandstorms,floods,mountain torrents and mudslides in western China.After years of continuous implementation of the policy of returning farmland to forests on the Loess Plateau,great achievements have been made.Among them,a total of 515 million mu of forests and grasses have been returned.The area of forests has accounted for more than 4% of the global green area during the same period.Bring many "ecological dividends."This article took the conversion of farmland to forest on the Loess Plateau as the background,mainly study and analyze the changes of vegetation coverage,precipitation and temperature in the Loess Plateau for many years;and analyze the impact of such significant changes in vegetation coverage on the precipitation and temperature of the Loess Plateau.The main conclusions are as follows:(1)The trends of vegetation NDVI,precipitation and temperature in the Loess Plateau have been obtained for many years.From 1982 to 2019,the vegetation NDVI of the Loess Plateau showed an overall upward trend,especially since the policy of returning farmland to forests was implemented in 1999,the maximum and extreme monthly maximum composite value of the vegetation NDVI of the Loess Plateau increased compared with before 1999.From the perspective of the spatial distribution trend,the vegetation NDVI of the Loess Plateau increases approximately stepwise from northwest to southeast,and the vegetation NDVI of more than 95% of the areas has increased significantly.Precipitation on the Loess Plateau shows a significant increase over time,and spatially shows a stepwise increase trend from northwest to southeast.The temperature in the northwestern part of the Loess Plateau is obviously lower than that in other regions.On the whole,the temperature range of the Loess Plateau has not changed much over the years.(2)It reveals the impact of different resolutions and physical parameterization schemes on climate simulation when using WRF mid-and short-term weather and climate models for numerical simulation,and obtains the optimal horizontal resolution and a set of better physical parameterization schemes suitable for the Loess Plateau region.When the horizontal resolution is larger,the simulation effect of precipitation and temperature is worse.When the horizontal resolution is 10 km,the spatial correlation between the simulated value and the observed value is 0.6121.The cloud microphysical parameterization scheme has little effect on the simulation of precipitation and temperature;when the Tiedtke scheme is selected in the cumulus convection parameterization scheme,the simulation of precipitation and temperature are closer to the real situation;the simulation experiment of the MYJ scheme in the boundary layer scheme Better than other programs.(3)The WRF model is used to analyze the changes in precipitation and temperature under different land use backgrounds,namely under different vegetation coverage conditions on the Loess Plateau.Through the analysis of measured data and simulated data,it is found that the response of precipitation to changes in vegetation cover is far greater than that of temperature,and that changes in vegetation cover have a positive correlation and regional influence on precipitation;changes in vegetation cover have little effect on temperature.