Response of kernel temperature vegetation drought index to urbanization in Northeast China

Clarifying the relationship between urbanization level and drought in the Northeast China is of great significance for ecological protection and the coordinated development of urbanization. We used kernel normalized difference vegetation index (kNDVI) instead of the normalized difference vegetation index (NDVI) in constructing the kernel temperature vegetation drought index (kTVDI). We then applied the Sen-MK method and Moran's index to analyze the spatiotemporal variation and spatial clustering of the kTVDI in the Northeast China from 2013 to 2022, and to examine the differences in kTVDI and their trends in areas with varying levels of urbanization and rural areas. The results showed that the correlation between kTVDI and soil moisture was stronger than that between temperature vegetation drought index (TVDI) and soil moisture in different years and periods. Additionally, kTVDI showed higher noise resistance in high-value areas compared to TVDI, making it more applicable to drought monitoring in the western part of Northeast China. From 2013 to 2022, drought intensity in Northeast China increased from northeast to southwest. Drought stress was stronger in spring and autumn, while that in summer was weaker, with a trend of worsening in spring and alleviating in summer and autumn. The Lesser Khingan Mountains, Changbai Mountains, and eastern Heilongjiang region formed a low-low clustering area for kTVDI, while high-high clustering areas were mainly distributed in the western Liaoning hills and the northeast plain. The expanding high-high clustering area largely overlapped with the urban triangle region of Harbin, Changchun, and Jilin, indicating that human activities within this urban cluster strengthened the drought. Areas with different levels of urbanization all experienced intensified regional drought, with moderate levels of urbanization having a stronger impact on the exacerbation of drought than high levels of urbanization. Urban green spaces could somewhat mitigate the impact of urbanization on drought.