The Impact Of Biological Crusts On The Dust Emission Scheme In Asia

The sand and dust storm is a catastrophic weather phenomenon that affects the world.In order to ensure the accuracy of sand and dust storm forecasts,accurate earth surface conditions are very important for dust emssion.There are many factors that affect the surface conditions.One of them is the surface biological crusts which have not been considered in most dust emission schemes.One reason is that there is no biological crust distribution that covers the sand source areas of Asia that can be used for sand and dust emission models.Another reason is that there is still a lack of quantitative research on how the crusts impacts on the dust emission.Therefore,in order to study the impact of crusts on sand emission,this thesis uses MODIS satellite surface reflectance data from 2000 to 2019 to invert the distribution of biological crusts in the source areas of sandstorms in Central and East Asia.And this paper also studies how the biological crusts impact on sand emission in source areas from the relationship between crust coverage,surface roughness and sand flux.The results show that biological crust is widely distributed in sand and dust source areas of Central and East Asia,with coverage rates of about 19.8% in Central Asian deserts,about 23.1% in the Gobi Desert,and about 17.3–32.8% in Chinese deserts.From the perspective of time change characteristics,There are two trends of the changes of biological crusts from “00 dust weather prevalence years” to “10 dust weather prevalence years” characterized by cyanobacteria crusts.One is in the deserts of Central Asia where cyanobacteria crusts are reduced in areas with high desertification,and cyanobacteria crusts with low desertification are increased.The changes in the deserts of Central Asia shows the deteriorating trend of the environment.The other is in Onqin Daga and Horqin sandy Areas where the crust of cyanobacteria in areas with low desertification is reduced,and the crust of cyanobacteria with high desertification is increased,showing a trend of improvement in the desert environment.Analyzing the reasons for the changes of biocrust in different deserts from “00 prevalence years” to “10 prevalence years”,the reduction of biological crusts is consistent with the increase of desertification in central Asian deserts.In the Gobi Desert,due to both the climate changing and human activities such as grazing,biological crusts have also been destroyed.Contrary to the Gobi Desert,in China,the coverage of biological crusts has been improved due to the conversion of farmland to forests and grazing land.All in all,the coverage of biological crusts is affected by both the climate changes and the pattern of anthropogenic activities.The results also show that the biological crust increased the roughness length of East Asian sand and dust source areas by 0.14–0.62 mm.From “00 prevalence years” to “10 prevalence years”,the roughness length increment of foreign deserts was decreasing,while the roughness length increment was increasing,showing the increase of domestic biological crust inhibition ability.Roughness length increment was positively correlated with lichen crust coverage(r = 0.78).The suppression of dust emission due to biological soil crust did not change significantly among years during the study period.The horizontal and vertical dust flux inhibition coefficients were about 2.2–26.6 and 1.7–2.9,respectively,clearly showing a suppressive effect for dust emission.Therefore,the impact of biological crusts should be considered in sand and dust storm forecast models.