Research On Spatiotemporal Changes Of Vegetation Cover And Its Response To Hydrothermal Conditions In The Mongolian Plateau Using Modis Data

Vegetation is an important part of terrestrial ecosystems,And plays an important role in global change.Vegetation as an indicator of changes in the ecological environment,that is affected by changes in hydrothermal conditions,but also has a positive feedback on hydrothermal conditions.Therefore,the change of vegetation cover and its response to hydrothermal factors is the focus of ecological research in recent years.Mongolian plateau is located in the middle of the Eurasian continent and plays an important role in the global carbon cycle.Its ecosystem status and its changes have an important impact on the environment in North China and the whole of Northeast Asia.Therefore,it is important to study the temporal and spatial distribution pattern,the change process,the driving mechanism and the response intensity of the vegetation coverage at different scales in the Mongolian Plateau.This is important for maintaining regional ecological balance and building ecological barriers,as well as for global environmental change research.In this paper,It use 2000-2015 MODIS /NDVI,LST,LSWI data,administrative divisions and vegetation type vector,And uses the mean method,the linear regression analysis method,the correlation analysis method,which study the changes of vegetation cover and surface hydrothermal conditions in Mongolian Plateau during 2000 to 2015.Also,it disscus relation between vegetation cover change and surface hydrothermal factors.(1)The Mongolian Plateau is dominated by the Ejina Banner of Alashan League,Which vegetation coverage formed an arch distribution in the direction of northeast and NDVI is gradually increasing.This regular pattern is closely related to the spatial distribution of vegetation types and hydrothermal factors in the study area.The surface hydrothermal condition corresponds to the NDVI distribution,but there is no coherent arc distribution due to the difference in terrain and latitude.LST distribution pattern formed the general trend of increasing the southwest to the northeast,while the LSWIdistribution pattern was opposite to the LST.The distribution pattern of NDVI in three seasons is about the same as that of growing season.On the whole,the spring vegetation coverage is the lowest,summer vegetation is the best.The seasonal variation of vegetation in the Gobi desert area in the southwestern part of the Mongolian Plateau is not obvious,while the seasonal variation of vegetation coverage in the central and northeastern regions of the Mongolian Plateau is significant,especially in the grassland vegetation area.(2)During the period from 2000 to 2015,NDVI showed an increasing trend both in the whole plateau and in different administrative regions of the two countries,which surface hydrothermal factors showed an increasing trend.In the seasons,three seasons NDVI showed an increasing trend.Among them,summer NDVI increased most significantly,and the same period of LSWI changes most significant.The spring and autumn NDVI and LST and LSWI show no significant increasing trend.The change trend of NDVI in different vegetation types showed that the shrub,sandy vegetation and farmland NDVI was improved obviously,and the other six vegetation types NDVI showed no significant change.(3)From the space distribution of the growing season NDVI,The total area of the entire study area accounted for75.23% showed an increase trend,which showing significant increasing or significant increasing trend area distributed in the Inner Mongolia region,including the southwest of Alashan League,the eastern and northern Ordos,the south of Chifeng,the southeast of Tongliao City And the northern part of Hanggan League,And scattered distribution distribution in the Mongolian,Dornod Aymag and ?v?rhangay Aymag.The Mongolian Plateau NDVI showed a decreasing trend area is mainly no significant reduction trend,and the distribution is scattered.At the season scale.The area of summer NDVI,showing increasing trend,is largest area in summer area,accounting for 77.6% of the plateau area,which account for the total area of the whole study area 77.6%.and the area of increasing trend in spring and autumn,accounting for the total area of the study area 63.2 % and 66.84% respectively.And the regions showing asignificant increases in the seasons were distributed in Inner Mongolia.(4)From the NDVI in response to the hydrothermal factors analysis the Mongolian Plateau,The correlation between NDVI and LSWI was higher in each season and growing season,which correlation coefficient was above 0.8.While in different district,LST influencing degrees and rules to vegetation co verage are vary in different seasons.The region of showing positive correlation between NDVI and LSWI,showed negative correlation between NDVI and LST.In contrast,The region of showing negative correlation between NDVI and LSWI,showed positive correlation between NDVI and LST.At the season scale,Except for Alashan League and northern mountainous areas,The spring appropriate LST and LSWI promoted the growth of vegetation in Mongolian Plateau,while LSWI in summer and autumn was the main factor to promote the growth of vegetation cover.From the characteristics of lag response,we can see that the LST in spring and summer limit the late stage of vegetation growth.The LSWI had no significant effect on the vegetation growth in summer,but the summer LSWI could promote the vegetation growth in autumn.(5)From the correlation analysis of monthly NDVI and earlier stage hydrothermal factors in Mongolian Plateau.In the period of vegetation turning green and withered,LST did not have obvious lag effect on NDVI,while,in the vigorous growth stage,LST had a significant lag effect on same stage and late period NDVI,limiting the vegetation growth.LSWI has a dominant role in vegetation growth in the whole growing season,especially in the same month and next month.Based on the remote sensing data,this paper simulated the temporal and spatial variation of vegetation cover and its hydrothermal conditions in the Mongolian Plateau during 2000-2015 year,and analyzed the correlation between NDVI and LST,LSWI.The hydrothermal condition data of surface temperature and surface water index can accurately represent the hydrothermal condition in the study area and have a strong response to vegetation cover.The results of this study will be of great significance to theecological research in North China and the whole of Northeast Asia.