Research

Here we present a brief overview of the different research topics the VITO urban climate service centre is working on. Click on the links in the left navigation panel for a more elaborate description. At the bottom of the navigation box you can also find an overview of different scientific publications and reports our group has contributed to.

UrbClim - A Fast Urban Climate Model

In a series of projects funded by the EU and ESA (the European Space Agency), the VITO urban climate team has developed a computer model, UrbClim, to simulate urban heat island intensity. Based on the physical equations that govern the exchange of heat between the urban substrate and the overlying atmosphere, the model typically generates maps containing hourly 2-m air temperature for an urban agglomeration and its wider surroundings, at a spatial resolution ranging from hundreds of metres to a few kilometres. It has been designed to be geographically flexible, i.e., it can be implemented nearly anywhere in the EU (and beyond) at a modest effort.

UrbClim is composed of a land surface scheme containing simple urban physics, coupled to a 3-D atmospheric boundary layer module. In the land surface scheme, urban terrain is represented as an impermeable slab with appropriate parameter values for albedo, emissivity, and aerodynamic and thermal roughness length, and accounting for anthropogenic heat fluxes. Despite its simplicity, UrbClim is found to be of the same level of accuracy than more sophisticated models. At the same time, the urban boundary layer climate model is faster than high-resolution mesoscale climate models by at least two orders of magnitude. Because of that, the model is well suited for long time integrations, in particular for applications in urban climate (adaptation) projections.

Urban climate observations

Next to the development of numerical simulation tools, the urban climate group has also built expertise in experimental measurement campaigns.Using professional Campbell Scientific monitoring equipment, we are now operationally monitoring the urban heat island intensity in the Belgian city of Antwerp. The monitoring sites are equipped with air temperature and relative humidity probes, 2D sonic wind meters and pyranometers to measure the shortwave downwelling solar radiation. In order to reduce errors from radiation loading on the air temperature measuremens, our group uses both passively as well as actively ventilated radiation shields. Next to the fixed monitoring stations, our group posesses a number of easy-deployable autonome temperature/humidity loggers. These loggers can be used to temporarily (e.g. during a summer period or in dedicated projects) monitor the urban climate in a city. These Onset HOBO data loggers are housed in actively ventilated radiation shields as well for encreased accuracy.

Our group is continously looking for new, innovative ways of urban climate monitoring including participatory sensing and development of a low-cost, actively ventilated autonome monitor for large scale deployments.

Usage of thermal remote sensing imagery

ASTER LST Image at 90 m , 24 july 2012 at 11:57 UTC

Our group also has a strong interest in using thermal infrared remote sensing data for urban climate studies. During the ESA Urban Heat Island project, the VITO urban climate group developed a data assimilation module integrating satellite retrieved land surface temperature images into the URBCLIM model. Our group makes use of different satellite data sources, including the geostationary MSG-SEVIRI with high temporal, coarse coarse spatial resolution LST data, 1 km TIR radiometers such as MODIS, AVHRR and (A)ATSR as well as high resolution imagery from ASTER (~90m) and Landsat (~120m/60m).

Remote sensing imagery, much like mobile measurements can provide a very visual way of studying the urban climate. However, one has to be carefull for interpretation of the imagery. Land surface temperature is derived from thermal radidation emitted by the surface and is not the same as the air temperature, which is strongly determined by turbulent transport and larger scale atmospheric conditions. Furthermore, directional effects resulting from the sensor viewing angle can cause significant errors in the surface temperature. Afterall, the heat radiated from the facade of buildings is different than the heat radiated of roofs and the surface.

Microscale urban climate modelling

Many of the possible climate change adaptation and mitigation measures which local policy makers or individual citizens can take, are typically on a building or microscale level. In order to quantify these