摘要: 土地利用/覆被变化(LUCC)不仅通过直接改变地表特性，而且通过进一步改变地表–大气相互作用过程来影响区域气候。城市用地扩张作为LUCC在人口聚集区的一种典型情况，对水文气象关键变量大气湿度产生强烈影响。本文利用站点观测数据，对1965~2017年长江中游城市群大气湿度指标进行趋势分析，发现该区域存在明显城市干岛(UDI)效应，具体表现为相对湿度和水汽压差变化速率最高分别达到每十年−1.977%及0.588 hPa。在2001~2017年城市用地加速扩张时，进一步结合遥感数据分析，发现大气湿度指标与蒸散发间以及蒸散发与叶面积指数间均存在显著正相关关系，这表明LUCC通过改变生态水文过程影响了区域大气湿度。此外，该区域气温出现显著上升的时间远早于大气湿度出现显著下降的时间，而近年来气温不再表现出明显变化。因此，我们推测当城市用地扩张到一定规模时才会出现UDI效应，并且在当前城市扩张后期阶段，城市化引起的LUCC对大气湿度的影响要大于其对气温的影响。

Abstract: Land use/cover change (LUCC) affects regional climate not only through its direct changes of land surface properties, but also through its further modifications of land-atmosphere interactions. Urban land expansion, as a typical case of LUCC in highly populated areas, would inevitably have a strong influence on atmospheric humidity, a key variable in hydrometeorology and climate. We employed observation data to examine atmospheric humidity changes by trend analyses of humidity indicators in the midstream urban agglomeration along the Yangtze River during 1965 - 2017, and found the evident urban dry island (UDI) effects which are characterized by significant relative humidity decrease 1.977% and vapor pressure deficit increase 0.588 hPa per decade, respectively. Furthermore, combining observation and remote sensing data, significant positive correlations between humidity and evapotranspiration, and between evapotranspiration and leaf area were detected during 2001 - 2017 when cities entered the accelerated stage of land expansion, indicating that LUCC affects regional atmospheric humidity through an eco-hydrological way. Besides, the obvious rise of air temperature was captured much earlier than the decline of atmospheric humidity, and air temperature has not shown marked changes in recent years. Thus, we speculated that the UDI effect will not appear until urban land expands to a certain scale and urbanization-induced LUCC may exert a larger influence on atmospheric humidity than on air temperature in the current later period of urban expansion.