Modeling the radiation balance of different urban underlying surfaces

Abstract

An urban net all-wave radiation parameterization scheme is evaluated using annual datasets for 2010 recorded at a Beijing urban observation site. The statistical relationship between observed data and simulation data of net radiation has a correlation coefficient of 0.98 and model efficiency of 0.93. Therefore, it can be used to simulate the radiation balance of Beijing. This study analyzes the variation in the radiation balance for different underlying surfaces. To simulate radiation balance differences, we set four pure land-cover types (forest, grass, roads, and buildings). Keeping all other conditions inputted unchanged, we model the radiation balance by changing the land-cover type. The results show that the effects of different underlying surfaces on radiation differ, and that there is much upward long-wave radiation, accounting for 84.3% of the total radiation energy falling incident on the land surface. The annual averages of net radiation for the four land-cover types are in the range of 38.2-53.4 W/m 2 . The net radiation of the grass surface is minimal while that of the roads surface is maximal. Additionally, with urbanization the net radiation values of common types of land-cover change, such as conversion from forest to roads, grass to roads, and grass to buildings, all have increasing trends, indicating that net radiation usually increases with urban sprawl. Land surfaces interact with the atmosphere through the exchange of water, energy and momentum. Any changes in energy flux between the land and atmosphere will affect the atmospheric thermal conditions and atmospheric circulation. The underlying surfaces (land use/land cover classes) greatly affect the climate according to their physical properties, such as the surface albedo, roughness, and emissivity [1]. The components of the radiation balance, the net radiation in particular, are main components of the land surface energy budget and are important physical and ecological parameters in the land-atmosphere energy exchange and redistribution [2]. The relationship between the type of urban underlying surface and the radiation energy budget is a core issue of urban climate. The effect of the urban land surface energy flux on local climate has been verified in many studies [3]. Therefore, systematic analysis of the urban radiation balance of various underlying surfaces is a basis and prerequisite for urban energy balance studies, and it is also important in understanding change processes of urban energy for different underlying surfaces and local climate caused by urban sprawl [4].The basic characteristic of urban landscape is the spatial heterogeneity of its land surfaces, and differences in landscape composition lead to the nonuniformity of energy transmission and distribution. Urban land surface is a complex physical interface. As surface characteristics change, the thermodynamic and kinetic properties of underlying surfaces can substantially change. All these disturbance factors will result in city-specific climatic characteristics. Most previo...

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