Spatiotemporal dynamics and influencing factors of urban dry island intensity in Nanjing Metropolis, China

With changes in the natural environment and the influence of human activities, the urban dry island (UDI) effect has gradually intensified globally, which has a great impact on the quality of life of urban residents. In this study, we analyzed the spatial and temporal characteristics of the UDI effect based on hourly relative humidity data from 54 meteorological stations in Nanjing metropolis and analyzed the effects of natural and human factors on changes of urban dry island intensity (UDII) using Geodetector tools and partial least squares structural equation modeling (PLS-SEM). The results of this study revealed the following. (1) The UDII in Nanjing metropolis showed a fluctuating downward trend between 2014 and 2020, and there were obvious differences between different seasons and between day and night, with the UDII being stronger at night and in winter. The UDII is strongest in the city center and gradually weakens toward the city periphery. (2) The average effects of human and natural factors in UDII are 0.42 and 0.31, respectively, indicating that human influences play a more prominent role in shaping UDII. (3) Urban structure (US) is a key latent variable that exacerbates UDII, whereas blue–green space (BGS) has a mitigating effect to a certain extent, and meteorological conditions (MC) indirectly exacerbate UDII by acting on blue–green space (BGS). (4) Although natural factors, such as air temperature (AT) and the fraction of vegetation cover (FVC), are also influential, their effects have been heavily modulated by humans in the context of high urbanization, which further highlights the dominant role of humans in UDII. This study provides new perspectives for understanding UDII and a scientific basis for optimizing the urban layout and improving the urban environment.