Evolution of urban built-up areas and its impact on urban vegetation of Jinan City, Eastern China

The expansion of built-up area is the basic manifestation of urbanization. The surge of urban built-up area has a great impact on the growth of vegetation inside and outside the built-up area. In view of the expansion of built-up areas and the change of vegetation in Jinan, this paper selects the night lighting data of NPP/VIIRS from 2014 to 2021, uses the reference comparison method to obtain the best threshold area, and extract the built area. This paper explores the spatio-temporal characteristics of the expansion of built-up areas in Jinan through the expansion speed, expansion dynamic degree, compactness and other indicators. On this basis, Landsat 8 OLI/TIRS data are introduced in order to study the vegetation changes in the urban built-up area from the aspects of vegetation coverage and growth status, the influence of human factors on vegetation, and the stability of vegetation in the built area from 2014 to 2021. The results show that the built-up area of Jinan has expanded from 469.5km² to 839km² in 2014–2021. The urban expansion has experienced a process from medium-speed to high-speed expansion, from dispersion to centralized expansion. In terms of the average value of NDVI, the condition of vegetation became worse from 2014 to 2016, and improved from 2016 to 2021, and the mean distribution of NDVI had obvious spatial difference, which was generally smaller in the central and western regions than in the east. The stability of vegetation in the built area is generally weak, and the ability of vegetation to resist adverse environment decreases. In the process of expansion, the influence of human on vegetation in most built-up areas is weakening.