Progress in numerical modelling for urban thermal environment studies

Urbanization is progressing rapidly in many Asian cities. The process of urbanization has modified the land use from natural environment into built environment. It alters not only the surface energy balance of the urban canopy, but also brings about a great quantity of anthropogenic sources of waste heat through air-conditioning, cars, etc. In addition, the effect of urbanization on urban wind environment is likewise significant. Thus, the primary precondition is to understand how the urban environment affects the physical and climatic pattern in and around the city resulting from urban encroachments. Commonly, wind-tunnel measurements and observational campaigns enable us to understand the physical processes that take place with the morphology of urban areas. This understanding is then used to represent these processes within numerical models of different urban scales. The ever-increasing computational power together with high- resolution computational fluid dynamic models has now become a useful tool to gain significant insight into detailed processes occurring within the urban context. This chapter gives an overview of the latest simulation studies for mesoscale and microscale climates, and also the assessment tools used in urban climate research. Various assessment tools are introduced and classified according to corresponding modelling scales. Next, the chapter addresses recent achievements in urban climate research for urban thermal environment studies. Examples of numerical results obtained by researchers of Japan are presented.