Evaluating the urban climate using geo-database – GEOCLIM TOOL

International audienceHow urban areas influence on microclimate is a primary concern to adapt city planning and to mitigate the impacts of the combination of the global warming and urban heat island. In this paper, we present a new urban climate model at district scale, GéoClim Tool, which takes into account energy transfers (radiation, conduction, storage, convection, and latent heat), envelope material behaviors and uses (anthropogenic loads). GéoClim Tool processing chain is implemented in the OrbisGIS geographic information system (Bocher et al. 2008) using SQL requests and the Groovy interface. GéoClim Tool is developed using the geographical database BDTopo® produced by the French IGN. A pre-processing partitions urban territory in relevant elementary areas: the « city blocks » (Lesbegueries et al. 2009) which are defined from the road network to respect the spatial organization of the city and the building configurations. Although the present geo-databases can give some indications on façade materials properties, it is difficult to know the envelope composition or the building occupancy levels. To address these uncertainties different scenarios are proposed based on urban typology, year of construction and thermal regulation evolutions. After a morphological analysis at city block scale (Bernabé et al. 2014), a kmeans clustering technique (Forgy 1965) is used to identify seven types of urban blocks that can be found in most European cities. GéoClim Tool is constituted of different computation sub-models. A simplified method based on morphological parameters has been developed to evaluate the solar trapping effect and to predict radiative balance of urban structure (Bernabé et al. 2014). A wall thermal model is developed for each surface classes (grounds, walls and roof). GéoClim Tool evaluates the heat budget of a building based on the assumption that it is a single box for each city block. It gives an average room-air temperature or the building energy demand. Energy balance is written at city block scale taking into account the interactions of each city block with its neighbors to obtain the air temperature, at middle height of buildings. GéoClim Tool outputs are the different energy fluxes, surface and air temperatures and the energy consumption of buildings at city blocks scale. Those data can be observed hour by hour or integrated. Climatic indicators can be computed from model outputs to generate climate maps and help stakeholder to identify the city blocks that are the most vulnerable to urban heat island. To evaluate mitigating actions at city block scale of three cooling strategies are compared: surface albedo improvement, vegetation and water inputs