Study On The Influence Of Land Cover Change On Sand And Dust Emission In The North China From 2000 To 2020

The arid and semi–arid areas in northern China are one of the largest sources of sand and dust in the world.Wind erosion and its dust emissions have an important impact on soil fertility,air pollution,ecosystem,climate change and human health.In order to control soil wind erosion and sand and dust emissions,a series of ecological restoration projects have been implemented in China,such as“Grain to Green Program（GTGP）”（1999）,the“Beijing-Tianjin Sand Source Control Project（TNSDP）”（2001）,and the“Returning Grazing Land to Grassland Project”（2003）.The vegetation cover in northern China has changed significantly in the past 20 years.However,the impact of land cover change caused by these ecological restoration projects on sand and dust emissions in northern China is still controversial.Therefore,the land cover changes and its impact on sand and dust emissions in northern China since the implementation of the quantitative ecological restoration project can provide a scientific basis for the ecological environment protection of our country.Therefore,based on the atmospheric chemical transport model WRF-Chem（Weather Research and Forecasting model coupled to Chemistry）,this paper simulates and quantifies the impact of land cover change on sand and dust emissions in northern China from 2000 to 2020.The main research results are as follows:（1）Physical process and dust process parameters localization of WRF-Chem model and its applicability evaluation.By conducting the different combinations of physical process and sand and dust parameter schemes for the sensitivity simulation experiment,and combined with the observation and remote sensing data to evaluate the simulation results of each configuration scheme.So as to determine the localization plan of physical process and sand and dust parameter schemes for northern China,Which can better simulation the spatio-temporal process of meteorological elements and sand and dust emission in northern China.（2）The vegetation cover area shows an upward trend as a whole in northern China,and the land cover change has obvious spatial differences.By statisicsing and analyzing the land cover types data from2000 to 2020,it is found that the area of forest,water and built-up area shows an increasing trend in research period,and the change of built-up area is the most significant,with an increase of 37,010.06 km².In addition,the area of cultivated land,bare land,shrub-land and grassland decreased as a whole.Among them,the bare land area decreased most sharply,reducing a total of 16,027.81 km²,and the reduced part was mainly transformed into grassland,sparse vegetation and cultivated land.（3）The emission of sand and dust shows a decline trend as a whole in northern China,but there are obvious seasonal differences.The average annual sand and dust emission from 2001 to 2020 was 84.97μg m^-2 s^-1 in northern China,which showed a weakening trend as a whole.The highest and lowest year of sand and dust emissions were in 2004(101.1μg m^-2 s^-1)and 2008(67.63μg m^-2 s^-1),respectively.Spring is the period of high incidence of sand and dust activity,and the average annual sand and dust emission is as high as 140.81μg m^-2 s^-1.The year with the highest sand and dust emission is in 2004(191.35μg m^-2 s^-1),and the lowest is in 2008(120.05μg m^-2 s^-1).The average annual sand and dust emission in summer was97.69μg m^-2 s^-1,which was second only to that in spring.The average annual sand and dust emission in autumn was 59.29μg m^-2 s^-1,showed an upward trend in whole,with a total increase of 16.63μg m^-2 s^-1.And the annual sand and dust emission was the weakest in winter,with an annual average of 42.08,the year with the highest sand and dust emission is in 2001(58.7μg m^-2 s^-1),and the lowest is in 2020(30.56μg m^- 2 s^-1).（4）Land cover change has a significant impact on sand and dust emissions and there are obvious spatial differences.Generally speaking,the change of land cover type has an obvious inhibitory effect on sand and dust emissions in northern China,and there is a significant spatial difference in the reduction of sand and dust emissions.The areas with drastic changes in sand and dust emissions were mainly concentrated in the sand and dust source areas and nearby areas,because these regions’land cover changed a lot.The sand and dust emissions in other areas with a reduction range of 0–2μg m^-2 s^-1.The sand and dust emissions in the middle zone of the sand and dust source area obvious increase,while the peripheral areas decreased significantly.（5）The transformation of bare land into cultivated land and grassland has the most obvious inhibitory effect on sand and dust emissions,and the effect of the change of land cover type on sand and dust emissions has a significant seasonal difference.The reduction of sand and dust emissions from bare land to sparse vegetation is the largest,which is 10.62μg m^-2 s^-1,followed by the conversion from bare land to grassland and cultivated land,which can reduce the emissions of sand and dust by 7.47μg m^-2 s^-1 and 7.29μg m^-2 s^-1,respectively.The most significant changes in land cover types that inhibit dust emissions in spring,summer,autumn,and winter are the conversion of bare land to sparse vegetation,the conversion of bare land to arable land,and the conversion of bare land to grassland.The transformation of grassland into bare land and bare land can promote summer dust emissions,while it exhibits a inhibitory effect in spring,autumn,and winter;The conversion of cultivated land into built-up areas has a promoting effect on autumn dust emissions,but it exhibits a inhibitory effect in other seasons.In this paper,through the analysis of land cover change in northern China,it is found that the type of land cover in this area has changed dramatically in 2000 and 2020,and there are obvious spatial differences.Then,based on the WRF-Chem model,we simulated the temporal and spatial distribution characteristics of sand and dust emission in this area from 2000 to 2020,and it is found that the sand and dust emission in northern China tends to weaken during 2000–2020,and the high value area of sand and dust emission is concentrated in the sand and dust source area.Finally,on the basis of land cover change,combined with the simulation results,the impact of land cover type transformation on sand and dust emission is quantified.The results show that the impact of land cover type transformation on sand and dust emissions is different in time and space.These founds provide a certain reference for the implementation and effect evaluation of large-scale ecological restoration projects in northern China,and are of great significance for the construction and treatment of ecological environment.