It is known that rapid expansion in urban area exerts prominent effects on surface or near-surface temperature and the urban heat island effect. However, whether and how urban land expansion influences atmospheric humidity, a key indicator closely relating to human comfort and urban environment, warrant further investigations. By taking Guangdong Province as an example, in this study we examined the change in atmospheric moisture over South China during 1961–2014 and evaluated the urban expansion effects. We found a prominent drying tendency over Guangdong, as characterized by decreasing relative and specific humidities and increasing vapor pressure deficit. The drying trend has a positive correlation with urban expansion speed and exhibited regional differences, with particularly stronger trends in more urbanized and populated areas such as the Pearl River Delta. Using a dynamic classification of urban / rural stations based on time-varying high-resolution land use / land cover maps, we estimated that urbanization contributed to approximately 50% of the total drying trend in the urban areas of Guangdong. Possible mechanisms and processes underlying the urban expansion effect were also discussed. We suggested that the changes in atmospheric moisture and the urban expansion effect should be considered in future climate change mitigation, urban planning, and landscape design to support sustainable development in urban areas.

众所周知，城市地区的快速扩张对地表或近地表温度和城市热岛效应产生了显着影响。然而，城市土地扩张是否以及如何影响大气湿度是与人类舒适度和城市环境密切相关的关键指标，值得进一步研究。本文以广东省为例，研究了1961-2014年华南地区大气湿度的变化，并评估了城市扩张的影响。我们发现广东地区有明显的干燥趋势，其特点是相对湿度和比湿度降低，蒸气压不足增加。干燥趋势与城市扩张速度呈正相关，并表现出区域差异，在城市化和人口稠密地区（例如珠江三角洲）的趋势尤其明显。基于基于时变的高分辨率土地利用/土地覆盖图的城市/农村站点的动态分类，我们估计城市化贡献了广东市区约50％的总干旱趋势。还讨论了城市扩张效应的潜在机制和过程。我们建议在未来的减缓气候变化，城市规划和景观设计中应考虑大气湿度的变化和城市扩张的影响，以支持城市地区的可持续发展。我们估计，城市化贡献了广东市区约50％的总干燥趋势。还讨论了城市扩张效应的潜在机制和过程。我们建议在未来的减缓气候变化，城市规划和景观设计中应考虑大气湿度的变化和城市扩张效应，以支持城市地区的可持续发展。我们估计，城市化贡献了广东市区约50％的总干燥趋势。还讨论了城市扩张效应的潜在机制和过程。我们建议在未来的减缓气候变化，城市规划和景观设计中应考虑大气湿度的变化和城市扩张的影响，以支持城市地区的可持续发展。