chapter  9
Urban climate models CHRISTINEGEORG ATO UANDDENIA KO LO KOT S A
Pages 20

During the past few decades, environmental, physical and architectural research has caused a fast evolution in outdoor urban environmental models. Temperature changes resulting by the built-up setting affect people’s health and comfort in addition to energy consumption and air quality. For that reason it is significant for the urban planners to learn about air temperature variations between different land-use categories for both extreme situations and during average conditions. [1] Furthermore, it is also of great importance to be able to provide accurate predictions in the longer term for the future situation for the study of climatic conditions when designing a city. The flow of air and the thermal structure of the atmospheric boundary layer (ABL) is defined by the earth’s surface. In particular, the surface energy balance, the separation of energy at the surface into diverse kinds, and the roughness of surface establish the temperature and the vertical profiles of wind and temperature in the boundary layer. Urban areas alter the material and aerodynamic character of the surface, greatly affecting the surface energy balance, as well as the dynamic and thermodynamic nature of the boundary layer. These modifications to the local climate are the core topics of urban meteorology and urban climatology. [2] Concerns on negative effects of urbanisation on the environment make the characteristics of urban areas increasingly important in urban planning and building construction, particularly at high density cities. [3] The urban boundary layer (UBL) is the part of the atmosphere in which most of the planet’s population now lives, and is one of the most complex and least understood microclimates. Given potential climate change impacts and the requirement to develop cities sustainably, the need for sound modelling and observational tools becomes pressing. [4] Nowadays it is evident that the increase of urban temperatures has a serious impact on the energy demand of buildings by increasing significantly the energy consumption for cooling, while decreasing to some extent the energy consumption for heating. Moreover the urban landscape creates a climate which affects human comfort, air quality and energy consumption. Though, regardless of these facts, climate issues often have low impact on the urban planning process in practice. [5] The air flow in the ABL is characterised by turbulence, which is generated by wind shear (wind is approximately geostrophic at the top of the ABL but zero at the surface). Temperature gradients can either generate or suppress turbulence. [6] It is the layer where nature springs, humans live and all our activities occur and the pollutants disperse affecting the rest of the atmosphere. Furthermore, all meteorological conditions prevail considered for the study or forecasting of the climate changes, and the temperature variations.