Impacts of urbanization on urban-rural VPD disparities across different subregions in China: A quantitative analysis based on station-pairing and partial differential methods

The climatic disparities between urban cores and surrounding rural areas have become increasingly pronounced due to rapid urbanization. The vapor pressure deficit (VPD) serves as a critical meteorological indicator reflecting atmospheric aridity, and identifying the contributions of urban and rural climate factors on the urban-rural VPD disparities plays an important role in understanding urban climate and ecosystem development patterns. This study introduces a quantitative method, utilizing partial differential equations, to assess the relative contributions of two crucial meteorological factors—air temperature (T) and relative humidity (RH)—toward urban-rural differences in VPD. Analyzing daily scale data from 116 pairs of urban and rural stations across mainland China for the period 2000–2017, we derived several key findings: Urban areas generally exhibit higher VPD than surrounding rural areas, with a relative difference in annual VPD of about 21.6 %, and the disparity increases over time. Furthermore, the influence of urbanization on VPD responds differently across seasons and geographical conditions. The simulated trends in VPD urban-rural differences using the partial differential method align closely with the actual observed trends, validating the effectiveness of our quantitative analysis approach. The VPD urban-rural disparity shows greater sensitivity to shifts in RH, with sensitivity coefficients exceeding 1.5 times to changes in T in most cases. RH is the primary factor causing VPD urban-rural differences in mainland China, and the relative contribution of RH is about 2.5 times of T. The patterns of sensitivity and the contribution of factors exhibit notable variation among subregions. This study enhances the understanding of how urbanization affects regional climate and provides insights for assessing the environmental impacts of future urban expansion.