Dissipation of water in urban area, mechanism and modelling with the consideration of anthropogenic impacts: A case study in Xiamen

Dissipation of water (evapotranspiration and water vapor conversion in human water use activities) is one of the significant hydrological processes in urban area, which becomes more complicated with rapid urbanization. However, there are few systematic studies on water dissipation problems in urban area, and even the related concepts are unclear. This paper proposed the concept of urban water dissipation (UWD) to describe water vapor conversion in urban areas, and presented analysis on mechanism of UWD based on observing and monitoring experiments. The urban underlying surface was divided into five categories: buildings, paved ground, vegetation, water surface, and soil, in which the buildings have been scarcely discussed in terms of water dissipation. The dissipation of water in buildings plays a more and more important role in the urban water circulation system, as the water supply increases in urban areas. To reveal how much water is dissipated in the buildings, the main water dissipation processes in different kinds of buildings were analyzed, and the quantitative model was proposed. Based on the traditional evapotranspiration models for urban underlying surface and the proposed model for water dissipation in buildings, a new modelling system was built to simulate the total UWD. The new model system reflects the impact of human water use activities on urban water dissipation. It was applied in Xiamen city to simulate the UWD in 2000, 2005, 2010, and 2015. The results show that the UWD intensity increased with the urbanization process in Xiamen urban area in past 15 years. The UWD contribution rate increased for most land use types, except green land. For example, the water dissipation on residential land is the fastest growing one of all land use types, and its contribution rate surpassed that of green land to become the largest contributor in 2010. Because of the interference of strong human activities, the contribution rate of water dissipation on the social side continues increasing. The contribution rate of UWD on the social side was more than 40% in 2015, and it is still increasing.