| The development of regional ecohydrological theory system and the improvement of technical methods have important theoretical significance for the protection and restoration of lake-grass-sand system and the construction of ecological civilization and green development in China.In view of the large span of east and west of Inner Mongolia,the complex climatic zoning and the rich geomorphic units,based on the spatial and temporal variation characteristics of summer precipitation,vegetation index(NDVI),surface temperature,topography and land use in Inner Mongolia in recent 20 years,thesis makes an in-depth analysis of the evolution process of each element under different spatial characteristics,such as the same land type in different regions and different elevations of the same land type.In addition,a comprehensive comparative analysis of the spatial and temporal characteristics of summer precipitation in Inner Mongolia and the correlation between influencing factors was carried out at different levels.The conclusions are as follows :1.Over the past 20 years,there have been spatial and temporal variations in precipitation,surface temperature,NDVI and land use in Inner Mongolia : the maximum precipitation occurred in 2007(39.5 mm)and 2018(72.5 mm),respectively,and the spatial and temporal variations in the 27.6-51.5 mm precipitation area are the most obvious;the surface temperature reached the maximum(36.4 ℃)and minimum(31 ℃)in 2007 and 2012.The surface temperature in the western region increased significantly,while the eastern region showed a downward trend.The overall variation range of NDVI value maintained within 0.12,and showed an indigenous downward trend in the western Ejina and central Daxing ’ an Mountains.The spatial and temporal changes of vegetation coverage(FVC)greater than 0.6 were most obvious,mainly distributed in the eastern part of Inner Mongolia.Among different land use types,urban and rural areas,residents,industrial and mining land are the most obviously affected by human beings.The land dynamic attitude index of this land type reached 25.52 % from 2010 to 2015,becoming the most obvious land type in the past 20 years.2.There is a significant correlation between NDVI value and precipitation in about41 % areas of Inner Mongolia,and NDVI values of different surface grazing cover types have different responses to precipitation changes.There is a negative correlation in the eastern forest area,and a positive correlation in the central grassland area.At the same time,there is a certain threshold for the positive response of precipitation to grassland vegetation.When the precipitation exceeds the threshold,the growth of vegetation will be inhibited.Furthermore,the area with negative correlation between surface temperature and precipitation accounts for about 74 % of the total area of Inner Mongolia,and there are some differences in the regulation of vegetation on surface temperature in different months in summer.3.The partial correlation results show that the correlation between precipitation and surface temperature is less affected by NDVI,while the correlation between precipitation and NDVI is greatly affected by surface temperature,and the influence degree of surface temperature in different regions is different.In the eastern region,precipitation and surface temperature play a promoting role in vegetation growth,and surface temperature is the main influencing factor.In the central region,vegetation growth is jointly promoted by surface temperature and precipitation.In the western region,surface temperature plays a leading role(inhibition)in vegetation growth,while precipitation has no obvious effect on promoting vegetation growth.4.In different precipitation areas,the strongest correlation between precipitation and surface temperature is in the middle and high precipitation area(correlation :-0.72),the strongest correlation between precipitation and NDVI is in the middle precipitation area(correlation : 0.40),and the strongest correlation between surface temperature and NDVI is in the middle precipitation area(correlation :-0.78).At the same time,the area with the most obvious precipitation change is the high precipitation area(the increase rate is 1.40),while the area with the most obvious surface temperature change is the medium-high precipitation area(the increase rate is:-0.07).The reason for this difference may be that there are certain differences in vegetation types and ecological climate corresponding to different rainfall areas.With the interaction between different factors,the relationship between various indicators in different regions is different.5.Under different spatio-temporal scenarios,the correlation between surface temperature of cultivated land and precipitation in the central region is the most obvious,and the correlation increases with the decrease of elevation.For cultivated land in the eastern region,the correlation between NDVI value and precipitation is the most obvious,and the correlation increases with the increase of elevation.The reason for this difference is that on the one hand,the climate zoning of cultivated land is different,on the other hand,the response relationship between different factors is different due to the difference of main crops in the central and western regions;the correlation between forest land precipitation and surface temperature is more obvious at low elevation(477–681 m);for different grassland types,the change of precipitation in meadow grassland lags behind that in other grasslands for about one year in some years.Compared with other land types,the NDVI value of grassland has the most obvious correlation with surface temperature,and the meadow grassland has the strongest correlation in the high altitude area(correlation :-0.88).Due to the differences in soil environment corresponding to different types of grasslands,this will directly lead to different dominant species of grasslands,resulting in a certain degree of difference in the relationship between precipitation and various indicators.In addition,affected by factors such as solar radiation at different elevations and regional climate environment,vegetation at different elevations has different responses to surface temperature and precipitation in the same grassland type.The surface temperature of unused land increased sharply in the past five years,and the maximum temperature could reach about 45.6 ℃.NDVI had the strongest correlation with precipitation in the middle elevation area(1163-1357 m),and other indicators had no correlation. |
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