Case Study 2.A Annex 5

Annex 5 Case Study Annex Case Study 2.A The Urban Heat Island of Antwerp 4.20 4.504.454.404.354.304.25 4.55 D. Lauwaet, K. De Ridder, B. Maiheu, and H. Hooyberghs 28 Vlaamse Instelling voor Technologisch Onderzoek (VITO), Antwerp 51.35 26 51.35 G. Lambrechts, L. Custers, and I. Gommers 51.30 51.25 51.20 51.15 City of Antwerp 24 51.30 Keywords Heat stress, urban climate model, 22 mitigation, adaptation, climate science 51.25 20 Population 1,015,000 (Demographia, 2016) (Metropolitan Region) 18 51.20 Area (Metropolitan 635 km² (Demographia, 2016) Region) 16 51.15 Income per capita US$41,860 (World Bank, 2017) 14 4.554.504.454.404.354.304.254.20 Climate zone Cfb – Temperate, without dry season, warm summer (Peel et al., 2007) Case Study 2.A Figure 1 Annual average number of heat wave days in the Antwerp area for the period 2081–2100, under the RCP8.5 climate scenario. Cities tend to be warmer than their rural surroundings, a phe- learned that the model achieves accuracy comparable to that of nomenon called the urban heat island, exposing urban residents existing traditional models, but at a speed that is more than a to much higher levels of heat stress than people living in the hundred times higher. As a result, UrbClim is capable of cov- nearby rural areas. At the same time, climate projections indicate ering periods long enough (tens of years) to deduce relevant that the frequency, intensity, and duration of heat waves is very climate statistics. likely to increase, and it is expected that, toward the end of this century, cities will be groaning under the strain of drastically This fast model was successfully exploited, coupling UrbClim increased levels of heat stress. to Global Climate Models (GCMs) contained in the CMIP5 archive of the Intergovernmental Panel on Climate Change (IPCC), and conducting simulations representing present (1986–2005) and Assessing the Urban Heat Island future (2081–2100) climate conditions (considering the RCP8.5 of Antwerp scenario). Based on the results for the present period, it was found that the urban area experiences twice as many heat wave days than Commissioned by the city administration of Antwerp the rural surroundings. Subsequently, when analyzing the climate (Belgium), the research center VITO started to map the current projections, it was found that, toward the end of the century, the and future heat stress situation in the city. Since climate projec- number of heat wave days is expected to increase by a factor of tions at the scale of urban agglomerations are lacking, a new nearly ten. Given the higher number of urban heat wave days to urban climate model (UrbClimTM) was developed that operates start with, city inhabitants will be facing almost one month of heat at an unprecedented horizontal resolution of a few hundred wave conditions each year (see Case Study 2.A Figure 1). meters (De Ridder et al., 2015). First, work was done to eval- uate the UrbClim model with meteorological measurements Mitigation and Adaptation Measures from five automatic weather stations, which were installed both inside and outside the city center to assess the ability of the Motivated by these results, the city of Antwerp decided to model to reproduce the urban heat island effect. From this, we implement mitigation and adaptation measures to tackle the 659 ARC3.2 Climate Change and Cities problem of heat stress. To achieve optimal results, the measures comfort of the people visiting these places. To be able to do are implemented simultaneously on three scales: (1) citywide, this, detailed information is needed on the local microclimate. (2) local, and (3) the individual. Therefore, VITO applied a meter-scale computational fluid dynamics (CFD) model (see Case Study 2.A Figure 2) to map Citywide Scale the focus areas and assess the effectiveness of potential adaptation measures. It is important to consider not only the air The construction of buildings in the city of Antwerp is reg- temperatures because human thermal comfort is also affected ulated by a building code, which all inhabitants and developers by radiation, humidity, and wind speed. An internationally rec- need to adhere to when renovating or constructing a building ognized indicator for thermal comfort that takes these vari- for which a city permit is required. In this code, specific instruc- ables into account is the predicted mean vote (PMV) (Fanger, tions are added that will help to reduce the heat stress in the city 1982), which scales between −4 (strong cold stress) and +4 over time: (strong heat stress). • For all roofs with a slope of less than 15% and a surface area of more than 20 square meters, it is obliged to install a green Since simulations with a CFD model are both computation- roof on top. This will drastically lower the temperature of ally expensive and time-consuming, it is not possible to do this the roof and, by retaining and evaporating rain water, the air for every renovation project in the city. Based on several sensi- temperature will be cooled. Additionally, green roofs provide tivity experiments and a review of the scientific literature, VITO extra isolation for the building. listed the expected impact of a number of adaptation measures • All private gardens and open parking lots need to be green on both the 2 meter air temperature and the PMV value during and permeable. Only 20 square meters can be paved in gar- a typical warm summer afternoon (Table 1). These numbers can dens of 60 square meters and only one-third in gardens of be used as first-order estimates for cities in a comparable climate 60 square meters. All outdoor private parking lots need to zone as Antwerp. The precise effect will depend on the local sit- have a permeable grassed surface. uation and should ideally be assessed with new CFD simulations • The majority of the buildings in the city center have historical or measurements. plaster facades. When renovated, these building fronts need to be painted in the original light, preferably white color. White buildings reflect more sunlight and will not warm up Individual Scale as easily as dark buildings, thereby reducing the heat radiation from these buildings. As mentioned earlier, the Antwerp urban area experiences twice as many heat wave days than the rural surround- Local Scale ings. This is problematic, since so-called heat health action plans are triggered using rural temperature forecasts only (as Regularly, large squares, parks, and neighborhoods in the in most countries). In order to remedy this issue, VITO has city are renovated. A new goal is to optimize the thermal set up a short-term (5-day) heat forecast system based on a Wind Speed (m/s) Table 1 Estimate of the effect of several adaptation measures on mean 2 meter 4 air temperatures and Predicted Mean Vote values during a warm day in summer. The 3.5 3 reference situation is a location covered with asphalt and concrete. 2.5 2 Mean 2 m 1.5 1 Adaptation measure Air Temp. PMV value 0.5 Ref: Asphalt/concrete = 4 Increase albedo −0.5°C 3.5 Grass area −0.5°C 3 Green roof/wall −0.5°C 3 Large fountain −1°C 3 Tree with dense crown −0.5°C 2 Several water sprayers −1.5°C 2 Row of trees −1°C 1.5 Water nebulizers −2°C 1 Case Study 2.A Figure 2 Example of the output of the CFD model for the Large park with water −1.5°C 0 neighborhood of the cathedral of Antwerp. 660 Annex 5 Case Study Annex combination of the regular European forecast model and References UrbClim, which delivers specific information for each neighborhood of Antwerp taking into account the urban heat island Climate-Data. (2015). Climate-Data.org. Accessed October 9, 2015: http:// effect. Since the information is much more detailed, the aid en.climate-data.org/search/ resources, targeting mostly the vulnerable elderly and children, De Ridder, K., Lauwaet, D., and Maiheu, B. (2015). UrbClim - a fast urban can be devoted more efficiently to those places where they are boundary layer climate model. Urban Climate 12, 21–48. Demographia (2016) Demographia World Urban Areas (Built Up Urban Areas needed most. Furthermore, heat wave warnings will be dis- or World Agglomerations). 12th Annual Edition. St. Louis: Demographia. played on light panels in the streets and on the city’s website Available from: http://www.demographia.com/db-worldua.pdf. where citizens can find more information on what to do in case Fanger, P. O. (1982). Thermal Comfort. Robert E. Krieger. of a heat wave. Peel, M. C., Finlayson, B. L., and McMahon, T. A. (2007). Updated world map of the Köppen-Geiger climate classification.Hydrology and Earth System Sciences Discussions 4(2), 462. More information can be found at the website of the Urban World Bank. (2017). 2016 GNI per capita, Atlas method (current US$). Accessed Climate Service Centre (http://www.urban-climate.be). August 9, 2017: http://data.worldbank.org/indicator/NY.GNP.PCAP.CD Case Study 2.B Application of Satellite-Based Data for Assessing Vulnerability of Urban Populations to Heat Waves Stephanie Weber, Natasha Sadoff, and Erica Zell also high in certain neighborhoods (Romero Lankao and Qin, Battelle Memorial Institute, Columbus 2010). Evidence shows that urban populations with higher levels of sensitivity and lower levels of adaptive capacity generally suffer Alex de Sherbinin Table 2 Advisory group members. Center for International Earth Science Information Network (CIESIN), Columbia University, New York Name Organization Academic and Dana Tomlin Department of Planning, Keywords Heat wave, social sensitivity, health Private Sector University of Pennsylvania impacts, urban heat island, adaptation, Robert Azavea (geospatial analysis vulnerability, remote sensing Cheetham firm) Population 1,567,442 (U.S.

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