THIS – Tool for Heat Island Simulation: A GIS extension model to calculate urban heat island intensity based on urban geometry
Introduction
The worldwide known phenomenon called ‘urban heat island’ (UHI) is still a concern for the quality of life. Due to the properties and arrangement of their elements, urban centers tend to store more heat and develop higher air temperatures than those found in the outskirts of the city (or surrounding rural areas). For Hamdi (2010) and Mendonça and Monteiro (2003), the growth of UHI due to the increase in urbanization is particularly important for the influence on the estimation of global warming.
Among the factors that influence the intensity of the heat island, urban geometry can be highlighted. Urban geometry interacts with the exchanging radiation between the Earth and Sky by the phenomena of reflection, absorption and thermal storage. The geometric combination of horizontal and vertical intra-urban surfaces is often referred to as ‘urban canyon’ and generally measured by the height and width (H/W) aspect ratio, the relationship between the average height of the building in an urban canyon and the street width.
Among the analytical studies correlating urban geometry and the formation of heat islands, it is worth highlighting the study conducted by Oke (1981). This author developed an empirically based model for predicting the intensity of nocturnal heat islands based on urban geometry. According to this author, the increase in the H/W ratio corresponds to the decrease in the cooling rate of the urban environment in relation to the rural area. Due to the potentiality of the Oke model, adapting it to a contemporary approach is one of the aims of this paper. Therefore, exploring the model as a computational tool may open up possibilities of urban analysis and make it easier for researchers to use.
Among the computational tools available, Geographic Information Systems (GIS) stand out due to the number of spatial and numerical interactions of geographic objects. In addition to the storage capacity of GIS, they are able to treat and represent tabular data and make it possible to incorporate new techniques and methods into territorial planning.
Associating the issue of urban heat island to the management possibilities offered by a GIS, the purpose of this article is to check the influence of urban geometry on the maximum intensity of urban heat islands. Thus, a computational algorithm was developed as an extension of a GIS, by exploiting its potential to analyze and manage geographical data. In order to do this, the following steps were taken: analyze the theoretical-numerical basis (Oke model); develop a calculation algorithm and implement it in the GIS platform; and adjust the tool by simulation testing of urban scenarios.
Section snippets
Theoretical basis
This section presents some approaches concerning the relationship between urban geometry and heat islands, as well as some examples of using GIS in urban studies.
Methodology
In order to develop this research, a study of the theoretical-numerical basis (Oke's model) shown in the previous sections was followed using a proposal of a calculation subroutine. This was based on the parameter of H/W ratio, as in Eq. (1). The subroutine was then created to identify the potential of urban geometries in developing urban heat islands. Thus, comparing simulated data to an actual condition of a tropical city, adjustments were made to the algorithm, so that the subroutine could
Results
The adapted model was developed to provide higher correlation results with the measured data than those calculated by the Oke model. During validation, it was found that for all the points, the simulated data by Oke's model resulted in an R2 = 0.63 with a standard deviation of 2.20 °C (Fig. 7a). The simulated data by the adapted model resulted in an R2 = 0.92 with a standard deviation of 1.01 °C (Fig. 7b).
The results of the proposed simulation (Fig. 8 and Table 3) demonstrate that all scenarios of Z0 <
Discussion
The results of the simulations of the hypothetical scenarios showed that the increase in roughness does not stimulate the development of greater heat island. By specifically assessing the parameter of ‘urban geometry’ and setting the roughness to a value > 2.0, an increasing trend, less marked than the scenarios of UHImax with lower roughness, was observed.
Some effects of increased building height on the mitigation of UHImax were also found by Theeuwes et al. (2014). These authors obtained a
Conclusion
This paper proposed to verify the influence of urban geometry on the maximum intensity of the nocturnal heat island, applying a computational tool developed as an extension of a GIS. The simplified Oke model (1981), incorporated into the calculation subroutine, was adjusted to provide more approximate results to the reality of two Brazilian cities, which served as the basis for calibrating the model. The comparison between real and simulated data using the Oke model showed a difference in the
Acknowledgments
The authors would like to express their gratitude to the São Paulo Research Foundation (2012/00594-5) (FAPESP), the Coordination for the Improvement of Higher Education Personnel (8802/13-0) (CAPES) and the National Council of Technological and Scientific Development (CNPq) for their financial support.
References (39)
- et al.
Numerical study on the effects of aspect ratio and solar orientation on outdoor thermal comfort in hot and dry climate
Building and Environment
(2006) - et al.
Impact of street design on urban microclimate for semi arid climate (Constantine)
Renewable Energy
(2010) - et al.
Modeling study of the aspect ratio influence on urban canopy energy fluxes with a modified wall-canyon energy budget scheme
Building and Environment
(2010) Towards a prescription for the greater use of climatic principles in settlement planning
Energy and Buildings
(1984)Street design and urban canopy layer climate
Energy and Buildings
(1988)- et al.
Automated recognition of urban objects for morphological urban analysis
Computers, Environment and Urban Systems
(2012) - et al.
Urban heat island and wind flow characteristics of a tropical city
Solar Energy
(2014) Two decades of urban climate research: a review of turbulence, exchanges of energy and water, and the urban heat island
International Journal of Climatology
(2003)Numerical modelling of urban heat-island intensity
Boundary-Layer Meteorology
(2003)- et al.
Simulation of the mean urban heat island using 2D surface parameters: empirical modeling, verification and extension
Meteorological Applications
(2009)
An application of the urban energy balance scheme for a statistical modeling of the UHI intensity
The impact of canyon geometry on intra urban and urban: suburban night temperature differences under warm weather conditions
Pure and Applied Geophysics
Adensamento urbano e desempenho ambiental no centro da cidade de São Paulo
Estimating Urban Heat Island Effects on the Temperature Series of Uccle (Brussels, Belgium) Using Remote Sensing Data and a Land Surface Scheme
Remote Sensing
Sensitive study of the urban heat island intensity to urban characteristics
International Journal of Climatology
Simulation of surface urban heat island under ‘Ideal’ conditions at night. Part 1, theory and tests against field data
Boundary-Layer Meteorology
Development of empirical models for an estate level air temperature prediction in Singapore
Cited by (51)
The analysis of the spatio-temporal changes and prediction of built-up lands and urban heat islands using multi-temporal satellite imagery
2024, Sustainable Cities and SocietyDevelopment of a micro-scale heat island (MHI) model to assess the thermal environment in urban street canyons
2023, Renewable and Sustainable Energy ReviewsGeoprocess of geospatial urban data in Tallinn, Estonia
2023, Data in BriefSpatial and temporal analysis of urban heat island effect over Tiruchirappalli city using geospatial techniques
2023, Geodesy and Geodynamics