| Desert-oasis ecotone is the connection zone of material and energy exchange between desert and oasis.Its stability has a significant impact on the balance of supply and demand of ecosystem services in oasis.The ecotone located in the edge of desert is prone to land desertification,which will lead to the loss of local biological and economic productivity,and in most cases,it will cause the reduction of vegetation types and quantity and the continuous increase of surface bare soil.It is the key to evaluate the temporal and spatial changes of desertification and determine the driving factors of desertification.Using remote sensing dynamic monitoring can understand the distribution and causes of desertification,improve the efficiency of monitoring,early warning and mitigation,so as to determine the impact of the degree of land desertification more quickly,in order to cope with and adapt to the future risks related to land desertification.Taking the desert oasis ecotone in the southeast edge of the Tengger Desert as the research area,using the remote sensing images of 1986,1991,1996,2001,2006,2011 and 2018 to establish the Desertification Difference Index(DDI)model and sketch the desert boundaries in the remote sensing images of 1986,1996,2006 and 2018,monitor and analyze the dynamic changes of land desertification in more than 30 years.Using correlation analysis method to determine the main influencing factors of land desertification,and then to explore the role of these factors in land desertification.The desertification difference index model has achieved a better result for the classification of land desertification degree in the study area.The results show that the kappa coefficient is between 0.768 and 0.796,and the classification consistency of desertification difference index is significant.It is feasible to use DDI model to divide the degree of land desertification.The degree of land desertification in the study area is gradually reduced from west to East.Severely and moderately desertified land is mainly distributed in the Midwest of the study area,i.e.the northwest of Tunguragnur,mulengaole and the northwest of Balunbeli;lightly desertified land is mainly distributed in the Middle East,i.e.the middle of mulengaole,the west of Bayanhot and the southeast of Balunbeli;non desertified land is distributed in the east of mulengaole and Bayanhot.The cultivated land and forest land are mainly distributed in the eastern Helan Mountain area.From 1986 to 2018,the process of land desertification in the study area developed inversely,but the desertification expanded from 1996 to2001.From 1986 to 1991,the area of severe and moderate desertification land decreased to 396.67 km~2 and 211.09 km~2 respectively.From 1991 to1996,the proportion of desertification land was 91.32%,which showed a reversal trend.From 1996 to 2006,the area of moderate and moderate desertification land increased and the degree of desertification increased.From 2006 to 2011,the dynamic degree of non desertification land was the largest,which was 8.79%,and the area of severe desertification land decreased to 1067.91 km~2.From 2011 to 2018,the desertification land accounted for 85.97%of the total area,and the reverse desertification phenomenon improved.From 1986 to 2018,various types of land were transferred to each other,and the overall performance was that sandy land was transferred to non-sandy land.From 1986 to 1991,the moderately and severely desertified land were transferred to each other,and the areas transferred out were larger than the areas transferred in;from 1991 to 1996,the moderately and severely deserted land was mainly transferred to light and non-desertified land,and the desertification status was improved.From1996 to 2001,the transferred in area of desertified land was larger than the transferred out area,and the desertified area increased;from 2001 to2006,the transferred in area of desertified land was less,but the moderately and severely transferred areas were larger than the transferred area,and there is still a risk of desertification;From 2006 to 2018,moderately and severely transfers occurred,and the non-mildly desertified land transferred the most,and the degree of desertification decreased.From 1986 to 2018,the desert boundary moved significantly with time,and it was more obvious in the southern part of the study area(Barunbeili Town).In 1986-1996 and 2006-2018,the border moved westward,that is,on the desert side,with average moving rates of 57.15m/year and 78.50 m/a,respectively.From 1996 to 2006,it moved eastward,that is,on the oasis side,with the fastest moving rate,which is179.38 m/a.Meteorological factors have an important influence on the dynamic change of land desertification in the study area.Among them,the annual evaporation amount,the number of days of high wind and the number of days of sand storm have a significant correlation with the increase of land desertification area. |
PDF Full Text Request