Vegetation Change Under The Background Of Urban Expansion In China From 2000 To 2019

As the main body of China's new urbanization,with the rapid urbanization,a large number of vegetation land has been transformed into urban agglomeration development land,which weakens the function of urban agglomeration vegetation in soil and water conservation and climate regulation,and then leads to the emergence and intensification of many ecological environments.Therefore,it is necessary to deeply understand the change of urban agglomeration vegetation and analyze the effect of urbanization on vegetation on urban development The formulation and implementation of the sustainable development strategy of the group has important reference significance.However,at present,the research on vegetation cover change of all urban agglomerations in China is relatively scarce,and the research on the effect of urbanization on vegetation of urban agglomerations is relatively less.Therefore,based on the normalized difference vegetation index(NDVI),land use/cover,and meteorological(temperature,precipitation)data,this study analyzes the vegetation change of urban agglomerations in China from 2000 to 2019 by using the methods of spatial-temporal analysis and mathematical statistics and reveals the effect of urbanization on vegetation.The results are as follows:(1)In China,forest land,waters,construction land and unused land showed an upward trend,while the rest showed a downward trend.In urban agglomerations,there were differences in the change rate of various land use types.The Yangtze River Delta was the area with the fastest change of cultivated land and construction land.Woodland and grassland showed a rapid decline in the Northern Tianshan Mountains urban agglomeration.The waters of Shandong Peninsula urban agglomeration changed rapidly,and the unused land of Hohhot-Baotou-Erodos-Yulin urban agglomeration decreased rapidly.According to the transformation of land use types,about 32.80% of China's regional land use types were found to have changed during the study period,among which the area of grassland change was the largest,the main transformation type was unused land,and the increase of construction land was mainly cultivated land.(2)In the study period,the mutation test of NDVI showed that there is no significant mutation point in China and urban agglomeration,while the trend analysis shows that China and urban agglomeration are showing a significant upward trend(at95% significant level).About 1.25% of China's regional vegetation was significantly degraded,and about 59.26% of China's regional NDVI showed a significant upward trend.In urban agglomerations,the proportion of regions with significant degradation and improvement of vegetation was higher than that of China as a whole.In the urban agglomerations,the phenomenon of significant vegetation degradation was more serious in the Yangtze River Delta urban agglomerations.In Southern Guangxi and Chengdu-Chongqing urban agglomerations,large areas of significant vegetation improvement can be observed.(3)Urban agglomerations had dual effects on vegetation,but the area of vegetation improvement was larger than that of vegetation degradation in the area where urban development occupied vegetation covered land(cultivated land,woodland and grassland).Climate change and human activities have spatial heterogeneity on vegetation.The impact of human activities on vegetation has a wider distribution range than climate change in terms of intensity and significance.Human activities dominate the vegetation change in China.Moreover,human activities in China's old urban areas have played a role in promoting vegetation,indicating that the city is actively achieving greening.At the same time,along the gradient of urbanization intensity,NDVI value showed a downward trend,but the NDVI value of fully vegetated area showed an upward trend.