Urban heat

Introduction

Globally over 50% of the population lives in cities, in Europe this percentage even rises to 75%. This makes the urban environment the most important habitat for human beings. Living in this environment however poses some challenges. Due to the urbanization trend, impervious surface cover has grown immensely, reducing green spaces and open water surfaces. This results in lower evaporation and thus higher sensible heat fluxes, heating up the surrounding air. Secondly, incoming solar radiation is captured and stored in building materials. At night, the stored radiation is released, again heating up the surrounding air. Another important consequence of urbanization is the morphologic change of the urban environment. Due to low sky view factors stored heat cannot radiate back to the atmosphere at night. All these elements aide in the creation of an urban heat island (UHI). An UHI is a phenomenon where the temperature in the urban environment is higher compared to the surrounding rural areas (Figure 1).

Figure 1: Illustration of the thermal behaviour of a city

Urban heat islands in combination with heat waves, have proven to be a mortal combination for some population groups, such as elderly, young children and people with poor health. Trends show a global temperature rise and an increase of heat wave intensity and frequency. These trends will put pressure on the living conditions of the urban environment and it is thus highly necessary to investigate solutions to preserve the liveability of cities in the future.

Many adaptation and mitigation strategies can be used to reduce heat stress in cities: green and reflecting roofing types, changing the city morphology, intelligent shading, reduction of traffic and other anthropogenic heat inputs, etc. In the UrbanEARS project the main focus of the urban heat regulation will be on urban structure and how this impacts the thermal behaviour of neighbourhoods at the city wide scale.

Objectives

 

Our general aim is to define a local climate zone (LCZ) typology (Figure 2) that is far better suited to characterize urban climatic conditions than traditional land cover datasets typically employed for urban climate modelling. By using remote sensing derived information on the characteristics of green and built-up areas, we strive at improving the operational value of urban ecosystem services related to temperature regulation.

Figure 2: Local CLimte Zone scheme (adapted from Stewart and Oke, 2012)

More specifically we strive to:

  • Optimize the land cover input for the urban climate model (urbclim) from VITO. We aim to replace the CORINE based input by a LCZ input map;

  • Evaluate the urbclim model using in situ data;

  • Evaluate the thermal behaviour of the city of Brussels.

 

The end goal of the urban heat work is to provide urban planners with information the thermal behaviour of different LCZ’s in Brussels so in future these findings can be taken into account when developing scenarios for future urban growth.

 

 

 

Our Approach

 

For urban heat regulation purposes it is important to choose the appropriate scale of your research. This project works at a city wide scale and therefore it is important to study the local scale effects of morphology on the thermal behaviour. The LCZ scheme developed by Stewart and Oke (2012) is designed to do just that. We use a method developed by Bechtel et al to delineate LCZ maps spatially explicit. The proposed methodology has some downsides and does not always perform as desired. In Figure 3 you can see how we adapted the methodology to achieve better results.

Figure 3: Adapted (workflow B) methodology and LCZ map

The LCZ map is then used in the Urbclim model (Figure 4) to simulate air and surface temperature at a resolution of 100m. From this output the thermal behaviour of the city of Brussels can then be studied.

Figure 4: Urbclim input and output

Publications

Verdonck M.L., Hooyberghs H., Van Coillie F. (2016). Developing a remote sensing based LCZ map to model air- and surface temperature in an urban environment. NSABS conference proceedings (abstract + oral presentation). NSABS 2016 Antwerp.

Verdonck M.L, Demuzere M., Hooyberghs H., De Wulf R., Van Coillie F. (2016). Evaluation of the thermal behaviour of different ‘local climate zones’ in Belgium. EGU conference proceedings (abstract + oral presentation). EGU 2016 Vienna.

Verdonck M.L. & Van Coillie F. (2016). Local Climate Zone Mapping: A Case Study In Belgium. GEOBIA conference Proceedings (abstract + poster presentation). GEOBIA 2016 Enschede.

Bechtel B., Demuzere M.,Xu Y., Verdonck M.L., Lopes P., See L., Ren C., Van Coillie F., Tuia D., Fonte C.C., Cassone A., Kaloustian N., Conrad O., Tamminga M. and Mills G. (2017). Beyond the urban mask: Local climate zones as a generic descriptor of urban areas – Potential and recent developments. IEEE Conference proceedings (abstract + oral presentation). JURSE 2017 Dubai.

Bechtel, B., Demuzere, M., Sismanidis, P., Fenner, D., Brousse, O., Beck, C., … Verdonck, M.-L. (2017). Quality of Crowdsourced Data on Urban Morphology – The Human Influence Experiment (HUMINEX). Urban Science, 1–21.

Verdonck M.L., Okujeni A., van der Linden S.,  Demuzere M., Hooyberghs H., De Wulf R., Van Coillie F. (2017). Thermal evaluation of the Local Climate Zone scheme in Belgium. IEEE Conference proceedings (abstract + oral presentation). JURSE 2017 Dubai.

Verdonck, M.L., Okujeni, A., van der Linden, S., Demuzere, M., De Wulf, R., Van Coillie, F. (2017). Influence of neighbourhood information on ‘Local Climate Zone’ mapping in heterogeneous cities. Journal of Applied Earth Observation and Geoinformation, 62, 102-113.

Verdonck, M-L., Demuzere, M., Hooyberghs, H., Beck, C., Cyrys, J., Schneider, A., Dewulf, R., Van Coillie, F. (2018). The potential of local climate zones maps as a heat stress assessment tool, supported by simulated air temperature data. Landscape and Urban Planning, 178, 183-197.

This project is funded by the Belgian Federal Science Policy (Belspo) within the RESEARCH PROGRAMME FOR EARTH OBSERVATION - “STEREO III”.

© 2015 UrbanEARS