Refined dataset to describe the complex urban environment of Hong Kong for urban climate modelling studies at the mesoscale

International audienceUrban climate models are indispensable tools for the evaluation of climatic risks faced by the growing urban population. In order to accurately simulate the urban surface energy balance at a high spatial resolution, it is important to provide models with detailed input data that can adequately describe the spatial variation of land covers, urban morphology, construction materials, and building functions within an urban area. Using Hong Kong—a city well-known for its complex, high-rise urban environment—as the testing ground, this study aims to present a geographic information system-based workflow for the construction of a refined urban database. Firstly, maps of land cover tiles, pervious and impervious surface fractions, building height, and other input parameters required by mesoscale atmospheric models are derived from multiple data sources including administrative building data, satellite images, and land use surveys. Secondly, a total of 18 representative building archetypes, with their corresponding architectural characteristics and occupant behaviour schedules, are defined. This allows for models to take into account the radiative, thermal, and dynamic interactions between buildings and the atmosphere, as well as the anthropogenic heat fluxes. Finally, locally adapted ranges of urban morphological parameters for the different local climate zones (LCZs) are derived, enabling the expansion of data coverage to neighbouring areas of Hong Kong, where detailed urban data are not readily available. Uncertainties of the refined database and limitations of the LCZ scheme are also discussed so that a similar approach may be adapted and applied to other cities in the world

Influence of air conditioning management on heat island in Paris air street temperatures

International audienceProjections of future climate suggest increases in extreme temperatures particularly in mid latitudes. In addition, the effect of heat waves, which are becoming a major “summer killer”, is exacerbated in urban areas owing to the heat island effect. Air conditioning (A/C) is a key parameter for health problems in case of heat waves since, on one hand, it reduces mortality but, on the other hand, depending on the heat management, it can increase street temperature therefore increasing the air cooling demand. Results of a meso-scale meteorological model (MESO-NH), coupled to an urban energy balance model including a simplified building model (TEB), are used. Simulations based on a realistic spatial cartography of air-cooled chillers and cooling towers in the city of Paris and surroundings have been performed. The simulation period corresponds to the extreme heat wave in Paris: 9–13 August 2003. Five scenarios will be discussed: firstly a baseline without air-conditioning (NO-AC scenario); secondly the actual situation including individual air dry coolers, wet cooling towers and an urban cooling network relying on free-cooling (water-cooled A/C with the river Seine) (REAL scenario). A third scenario will assume that all the heat is rejected as sensible heat in the atmosphere (DRY AC scenario). Two other scenarios correspond to a prospective where A/C is doubled. Scenario 4 assumes that all the heat is rejected as sensible heat in the atmosphere (DRY ACx2 scenario). On the opposite, scenario 5 assumes that all the heat is rejected underground or in the river Seine (NOREJ scenario). Results show that A/C affects the UHI depending on its management. A detailed analysis on selected districts shows that the local temperature variation resulting from heat island is proportional to the sensible heat rejected locally by A/C, indicating that a clever A/C management is all the more important to provide comfort and to mitigate heat island. Moreover, the incidence of the sky view factor is also discussed

Sustainable management of urban pollution: an integrated approach

This paper presents a new decision-support framework and software platform for an integrated assessment of options for sustainable management of urban pollution. The framework involves three steps: (1) mapping the flow of pollutants associated with human activities in the urban environment; (2) modelling the fate and transport of pollutants; and (3) quantifying the environmental, health and socio-economic impacts of urban pollution. It comprises a suite of different models and tools to support sustainability appraisals including life cycle assessment, substance flow analysis, source and pollutants characterisation, pollutant fate and transport modelling, health impact analysis, ecological impact assessment, and multi-criteria decision analysis. The framework can be used at different levels, from simple screening studies to more detailed assessments. The paper describes the decision-support framework and outlines several case studies to demonstrate its application. The software tool is available free of charge at www.pureframework.org. Practical applications: The PUrE framework and software platform can be applied to assess and compare the sustainability of different technologies, products, human activities or policies. Example applications of the framework have so far included sustainability comparisons of technologies for thermal treatment of municipal solid waste; generation of electricity from coal and biomass; environmental and health impacts of a mixture of pollutants in Sheffield; the role of urban green space in reducing the levels of particulate matter in London and the impacts of environmental policy on legacy pollution in Avenmouth. </jats:p