Research Projects

The central objective of my research is to elucidate the physical basis of the human impacts on climate caused by urban development. It requires understanding the exchanges and balances of heat, mass and momentum as they are modified from those of the pre-urban landscape to their present state. This means working across a range of atmospheric scales (from micro- to mesoscale) and relating the modification of these processes to the climatic effects they evoke.  This cause-and-effect chain in cities is an analogue of the changes being wrought by humans at the global scale. My aim is to improve understanding of the ‘causes’ and ensure that ‘effects’ are properly assessed and linked to their genesis. This will mean we are better placed to initiate intelligent urban design strategies to minimize negative impacts and contribute towards more sustainable patterns of living. This is critical to the health of Earth, because cities are nodes of the most intense human impacts on climate and the source of most of the radiatively-active pollutants of concern to global climate.

Projects

In the past few years we have conducted the following work:

        Extending our database of surface energy balance (SEB) observations of cities - we conducted two field campaigns in European cities (Marseille, France – Grimmond, Voogt, Salmond & Roberts; and Basel, Switzerland – Voogt, Salmond, Roth, Soux and Doerksen & Satyanarayana) and are associated with work in Łódź, Poland – Offerle, Fortuniak, Grimmond & Klysik) and we have renewed observations in Vancouver, BC (Walsh & Doerksen). We were part of two major international projects (ESCOMPTE in Marseille, and BUBBLE in Basel).

Left:  Tower (23 m) mounted on a roof (20 m) in the city centre of Marseille. Right: Tower (32 m) extending from street level to 17 m above roof level in Basel. Lift used to service instruments in the centre.

         Roughness length (z₀) and zero-plane displacement (z_d) - we completed and published a comprehensive survey and assessment of the roughness parameters z₀ and z_d for cities (Grimmond). The results fill in a gap that existed for very rough surfaces and a revised Davenport roughness scale was published (Davenport, Wieringa & Grimmond).

        Net radiation parameterization scheme - there are virtually no routine observations of net radiation in cities. A parameterization scheme (NARP) that requires only simple surface property and meteorological measures was developed (Offerle & Grimmond).

        Heat storage by the urban fabric - it is a challenge to quantify the portion of the surface energy balance taken into, and released from, heat storage by the thermal mass of a city. We published a study of this flux term in cities (Grimmond), applied four different approaches to data gathered in Marseille (Roberts, Voogt & Grimmond) and conducted detailed storage and temperature measurements in the Basel canyon (Voogt, Soux). Another study (Meyn) focussed on heat fluxes into and out of roofs.

  Left: View down the Basel street canyon (tower base on right side near cream trailer)
Right: Thermography of canyon and roofs in mid-afternoon.

        Evaporation - another challenge is to measure/calculate evaporation from the heterogeneous system of wet, moist and dry surfaces of a city. We have published analyses of urban evaporation (Grimmond), dewfall (Richards) and advection effects on evaporation in an irrigated urban park (Spronken-Smith & Lowry).

            1/8^th scale model of row houses, lawns, road and trees used to simulate urban dewfall.

        Urban CO₂ fluxes – direct measurements of the turbulent flux of CO₂ over cities has been conducted in Marseille and Vancouver (Walsh, Salmond & Grimmond).

        Local-scale Urban Meteorological Pre-processor Scheme (LUMPS) - several parameterization schemes and models generated by our group have been combined to form an urban preprocessor scheme LUMPS (incl. roughness methods, NARP, OHM and evaporation) (Grimmond and Offerle). LUMPS requires only standard weather variables and simple measures of urban surface cover (mean building height, fraction vegetated, etc.) to generate hourly values of all SEB fluxes (radiation, storage and turbulent transfer of heat and water vapour) and atmospheric stability

        Town Energy Balance (TEB) model – collaboration with Météo France (Masson, Grimmond & Lemonsu) to validate the Masson (2000) urban-scale weather forecast model.  The model has been embedded in the Canadian Global Environment Model (GEM) by Lemonsu, Belair and Mailhot of the Meteorological Service of Canada. A new joint project seeks to validate TEB for conditions specific to Canadian cities. This will be supported by new observational studies in Montreal (especially snow and anthropogenic heat) and Vancouver (especially irrigation).

        Radiative flux divergence –a new radiometer to measure directly the longwave radiative flux divergence within air – called a dual-channel infrared radiometer. It was designed by Nunez and deployed by Soux, in a Basel street canyon in the BUBBLE campaign.

 

Andres Soux with the dual-channel infrared radiometer
mounted over the centre of the Basel canyon top

        Scintillometry - we have collaborated on early studies in the use of long path-length scintillometry to measure area-averaged sensible heat fluxes over urban sites. Work conducted in Tokyo (with Kanda and colleagues and Roth), Marseille (with Lagouarde and Irvine) and in Basel (with Salmond, Roth, Satyanarayana).

The site for the scintillometer study in Tokyo. The tall crane with orange basket houses one of the instruments.	One end of the scintillometer path along the roof tops in Basel. Another path ran diagonally across the adjacent canyon top to the left.

        Anisotropy of surface temperature (T₀) and remote sensing - a numerical model (SUM) has been developed to predict what a remote sensor, placed at any point in space above a complex 3-D urban surface, ‘sees’ (Soux & Voogt) and a review of remote sensing in urban climate conducted (Voogt).

        Detection of subtle thermal effects of climate station disturbance - Runnalls devised an original technique to detect anomalies introduced into the homogeneity of historical temperature records by small site changes. The method is sensitive enough to identify anomalies that escaped the best techniques in use today.

        Urban heat island (UHI) controls and characteristics - a UHI study of Vancouver focussed on the controls underlying its temporal variation (Runnalls). Special attention focussed on the role of synoptic conditions, and a new, quasi-physical ‘weather factor’ was devised that incorporated wind and cloud effects. The study is the first to demonstrate the seasonal control exercised by rural thermal admittance (largely soil moisture). An algorithmic scheme of hourly UHI was applied to data from Uppsala, Sweden and Lodz, Poland (Barton).

      Canyon Venting - studies in Marseille and Basel are directed to investigate the rold of urban street canyons in the venting of heat and CO₂ and its relation to above-roof conditions.

 Funding and Field Support

            My research in urban climate has been funded throughout by the Natural Science & Engineering Research Council of Canada (NSERC) and recently by the Canadian Foundation for Climate and the Atmospheric Sciences (CFCAS). The ESCOMPTE study was partially supported by the Conseil National de Recherche Scientifique of France. Excellent support in Basel was provided by colleagues at ETH (Rotach) and Basel (Vogt and Parlow).