Effect of urban expansion on atmospheric humidity in Beijing-Tianjin-Hebei urban agglomeration

Accelerated urban expansion has contributed to the urban-rural contrast regarding atmospheric humidity. However, the effect of urban expansion on atmospheric humidity is not understood well in the Beijing-Tianjin-Hebei urban agglomeration (BTHUA). In this study, observations from 133 meteorological stations were used to analyze the long-term trend of atmospheric humidity and the urban expansion effect in the BTHUA during the period 1961–2014. The urban expansion effect on atmospheric humidity was evaluated by calculating the differences in atmospheric humidity trends between urban and rural series based on the dynamic classification method using secular urban impervious data. The results revealed that a drying trend of annual and seasonal average atmospheric humidity was observed in the urban areas of the BTHUA during the period 1961–2014, characterized by decreasing relative humidity (RH), water vapor pressure (Ea), specific humidity (Q) and increasing vapor pressure deficit (VPD). A more prominent drying trend (p a and Q, respectively; p a and Q was the strongest in spring at 0.138 hpa, −0.237 hpa and −0.151 hpa per decade, respectively, while the urban expansion effect on RH was the strongest in winter, reaching −1.159% per decade. This study provides a better understanding of the relationship between variations in atmospheric humidity and urban expansion, as well as scientific support for urban planning. © 2020 Elsevier B.V.