Spatial-Temporal Changes And Driving Factors Of Desertification In Hebei Province

Desertification is a kind of land degradation phenomenon driven by many factors and complicated situation.It not only hinders the economic development of human society,reduces the living standard of human society,but also has a certain impact on the sustainable development of the country.Therefore,dynamic monitoring and driving factor analysis of desertification are conducive to grasp the development of desertification and provide theoretical support for desertification control.Taking Hebei Province as the research area,this thesis selects Moderate Resolution Imaging Spectroradiometer(MODIS)data from 2001 to 2018 to calculate the desertification index Normalized Difference Desertification Index(NDDI),and constructs the NDDI time series curve of desertification land by combining the survey data with MODIS data.The mean absolute distance between the NDDI time series curve of desertification land and the NDDI time series curve of Hebei Province was calculated.The threshold was set for the possible distribution of desertification,and the desertification information of Hebei Province was extracted.On this basis,the spatial-temporal evolution of Hebei Province was analyzed by using the linear trend analysis method,gravity center migration analysis,coefficient of variation,annual change rate and future trend analysis,and the response characteristics of desertification land area to temperature,precipitation and wind speed in the study area were discussed.Based on the geographical detector method,the impacts of climate factors and human activities on desertification were quantitatively discussed.The main conclusions are as follows :(1)The NDDI was calculated based on MODIS data,and the desertification time series curve was constructed combined with desertification survey data,and the noise reduction was carried out.The similarity comparison method was used to extract the desertification information in the study area,and the accuracy was verified.The overall accuracy reached 84.12 %.(2)The overall trend of desertification in Hebei Province was declining from 2001 to 2018,but there was still a deterioration in some areas.The focus of desertification in the study area is mainly concentrated in the southwest of Zhangjiakou,without obvious signs of desertification expansion,and the stability is mainly mild fluctuations.From the5,10,18 years of annual change rate,showed a downward trend.There is obvious spatial heterogeneity in the future trend,mainly in the continuous change.(3)The annual average precipitation in Hebei Province from 2001 to 2018 showed an overall growth trend,while the annual average temperature and wind speed showed a trend of decrease first and then increase.In terms of spatial pattern,precipitation showed an increasing trend from northwest to southeast,temperature showed a decreasing trend from northwest to southeast,and the average annual wind speed showed a distribution pattern of high-low-high from northwest to southeast.The correlation between annual precipitation and mean absolute distance(Characterization of desertification degree)is mainly positive,and the proportion of positive correlation between air temperature and mean absolute distance is 55.81 %.The proportion of positive correlation between annual wind speed and mean absolute distance is slightly larger than that of negative correlation.Geodetector results show that desertification is a complex and changeable land degradation phenomenon formed by a variety of factors.Soil types and annual precipitation in Hebei Province have the strongest explanatory power for desertification.