Conferenties at RMI location:Ukkel Belgium date:29 octobre 2012
There exists a large discrepancy between the rural and urban land cover in terms of soil water, aerodynamical, thermal and radiative characteristics, and anthropogenic heat. This results in urban-scale meteorological features such as the urban heat island, reduced wind speed and the city breeze. Some of these effects have a considerable impact on human health in cities when the nocturnal cooling is reduced during heat waves or when air quality is affected during smog episodes. Regional climate models and air-quality models are used to quantify, understand and mitigate these effects. Inside the CLM-community, which is the climate group affiliated to the COSMO consortium, a range of urban parametrizations for the regional climate model COSMO-CLM are currently tested with a variety in complexity and input parameters. At the same time, the air-quality model AURORA is developed and used at VITO, the Flemish Institute of Technological Research. The question rises what impact does urban climate have on air quality in cities.
The presented urban parameterization covers a simple and direct implementation of urban characteristics in TERRA_ML, the soil module of COSMO(-CLM), which has been tested 'offline' for Marseille and Toulouse. Besides the anthropogenic heat, specific dynamic, radiative and thermal parameters including roughness length, heat capacity, conductivity, albedo and emissivity are assigned for the urban land-cover. Furthermore, a bluff-roughness thermal roughness length parametrization is used. New surface-layer transfer coefficients are adopted which can deal with very small thermal roughness lengths typical for urban surfaces. A puddle storage for the urban impervious soil has been implemented.
The regional climate model COSMO-CLM updated with urban parameterization and the air-quality model AURORA are currently applied at a horizontal resolution of 1km over Toulouse (France). It is investigated whether air-quality modeling can be improved when forcing it with (urban) mesoscale meteorological data generated with COSMO-CLM rather than with coarser meteorological data from ECMWF reanalysis. Therefore each nesting step of COSMO is used subsequently as input for the air-quality model. In order to set priorities for the improvement of air-quality modelling in the future, the importance of orography, urban climate and the impact of uncertainty in pollutent emissions to air-quality modelling are investigated.