Study On Desertification Monitoring From 2000 To 2014 And Its Driving Factors Through Remote Sensing In Ningxia,China

Land desertification mainly occurs in ecologically fragile arid and semi-arid areas.Ningxia suffers from the serious desertification.In recent years,due to the improvement of natural environment and the implementation of national policy,the desertification in Ningxia has been gradually reduced,but the situation of desertification is still serious.This paper focuses on the analysis of the change characteristics and driving factors of vegetation cover and Rainfall Use Efficiency(RUE)in Ningxia during the growing season at the pixel scale,and elaborates the process and causes of the desertification in Ningxia in detail.Furthermore,in view of the driving factors for desertification,we put forward some reasonable suggestions for governance of desertification in Ningxia,which is of great significance to the ecological restoration.Using the MOD13Q1 data,DEM data,land use classification map and other remote sensing data,as well as non-remote sensing data such as meteorological data and social statistics data,supported by the software of Matlab and ArcGIS,carried out the evaluation of the status of desertification through spatial trend analysis,gravity center migration model and gray relational analysis and other methods.The paper monitored the degradation status of vegetation coverage from 2000 to 2014 in Ningxia and tried to use the rainfall use efficiency as the main index of desertification monitoring to analyze the status of desertification in Ningxia in recent 15 years.On this basis,the influence caused by terrain factors,vegetation types,meteorological factors and social factors on desertification were analyzed quantitatively.The main results are as follows:(1)According to the meteorological data of Ningxia from 1980 to 2014,the climate change characteristics in recent 35 years were analyzed.The temperature of Ningxia was increasing in the past 35 years.The precipitation was reducing in the south,stable in the center and increasing in the north,sunshine hours showed a decreasing trend.Relative humidity of the central rose,while the north and south reduced.The area where the temperature increased during 2000-2014 was mainly distributed in the northern part of Ningxia,accounting for 63.4% of the total area.The precipitation increased in the middle and south,and the sunshine hours decreased,especially in the southern region.Average relative humidity increased by north.Great difference was found in the mutation time of different meteorological factors in different districts of Ningxia,the abrupt time in the south generally lagged behind that in the north and center.(2)Based on the value of NDVI in the growing season,the dynamic changes of vegetation cover in Ningxia from 2000 to 2014 were analyzed.The vegetation coverage in the southern Ningxia and Yellow River irrigation areas was higher,the central desertification was serious and the vegetation cover was lower.In the past 15 years,the coverage of vegetation was mainly improved,accounting for 91.45% of the total area of Ningxia.The area of vegetation degradation only accounted for 5.79%,which was mainly distributed in the center of irrigation area and Helan Mountain.And through the continuous analysis of NDVI,the results show that the vegetation will continue to improve in the future.The center of gravity migration route of vegetation coverage showed that low vegetation cover gradually migrated to northern Ningxia and the higher vegetation coverage had a tendency to expand to the central.(3)Based on the accumulated NDVI and precipitation in the growing season,rainfall use efficiency(RUE)of the vegetation was calculated.The dynamics of land desertification in Ningxia from 2000 to 2014 were evaluated by analyzing the trend of RUE.According to the data of 2000,the area of desertification occurred in the period from 2000 to 2014,accounting for 7.79% of the total area,mainly located in Helan Mountain,Liupan Mountain,Yinchuan Central,Qingtongxia and part of Zhongning,where the vegetation have also been degraded.The proportion of desertification in 2005,2010 and 2014 accounted for 15.82%,11.61% and 7.79% of the total area respectively,so the proportion of desertification in Ningxia is gradually decreasing,and the center of gravity of desertification has a tendency to migrate to the north.The desertification in Ningxia was obviously affected by elevation and slope,and the proportion of desertification firstly decreased and then increased with the increase of elevation and slope.(4)Based on the analysis of the driving factors of vegetation dynamics and desertification in Ningxia,it was found that the correlations between NDVI,RUE and the influence factors have difference,especially in the precipitation and relative humidity,NDVI had positive correlations with the precipitation and relative humidity,while RUE had negative correlations with the precipitation and relative humidity.According to the grey relational analysis,it is found that the change of vegetation cover was mainly affected by meteorological factors,and the average relative humidity,sunshine hours and average temperature are the dominant factors of vegetation degradation.RUE was affected by meteorological factors and human factors at the same time.The sunshine hours,the average temperature,the relative humidity,the population and the animal husbandry were the main influencing factors of desertification.