Water vapor emissions from urban landscapes in Sakai, Japan

Abstract

Water vapor emissions in urban areas are important processes in urban hydrology and urban climate. We evaluated the spatial and temporal characteristics of water vapor fluxes, based on measurements at an urban center for six years, suburban landscape for five years, and urban park for one year in Sakai, Osaka, Japan. The magnitudes of the water vapor emissions were approximately half for the urban center and one-fourth for the suburb compared with evapotranspiration in a planted forest near the city. Anthropogenic water vapor emissions were estimated to be high in the urban center, resulting in higher water vapor emissions in the urban center than in the suburb. The water vapor emissions at the three landscapes were controlled by net radiation and surface wetness, where surface conductance decreased with days after a rain event. Evapotranspiration of the urban park was comparable to that of the planted forest due to the dry urban atmosphere, known as the oasis effect. The green fraction explained the spatial variation in the annual water vapor emissions. Based on the linear perturbation analysis, the changes in water vapor emissions by urbanization could be determined by a balance between increased anthropogenic water vapor emissions and decreased surface conductance.