Interplay between built environment factors and Urban Heat Island phenomenon in India and the United States
Proposal by Surekha Tetali,
PhD-BPD Candidate
Tuesday, 07 May 2019 | 12:00-2:00pm
MMCH 415 IW Large Conference Room
Advisory Committee:
Volker Hartkopf, Professor, School of Architecture, Chair
Nina Baird, Professor, School of Architecture
Kelly Klima, Engineer, Rand Corporation
Abstract:
Urban Heat Island (UHI) phenomenon is defined as higher urban temperatures compared to the rural surroundings. UHI phenomenon impacts building energy consumption, thermal comfort, air quality, and the overall human well-being in urban areas. Increased heat due to urbanization is a key cause of UHI phenomenon. While, the impact of UHI on building energy consumption has been well studied, a comprehensive understanding of the role of buildings and urban built environment in formation of the UHI has not reached the same level of maturity. Research on if and how the built environment interacts with UHI phenomenon at different spatial and temporal scales is scant, especially in a building scientist’s perspective. Further, research on UHI is predominantly focused towards temperate countries of North America and Europe. However, in hot and dense (sub) tropical country like India, UHI research is still in its infancy. Increasing temperatures and rapid urbanization in India show the immediate need for UHI research in India.
This research proposes to analyze the interplay between the natural and built environmental factors influencing the UHI phenomenon across some of the highly populated Indian urban regions and compare it with urban regions of the United States. UHI magnitude can be quantified as the difference between urban and rural land surface temperatures (LST) or canopy air temperatures. UHI quantified using LST is referred to as surface UHI (SUHI) and canopy air temperature as canopy UHI (CUHI). SUHI and CUHI are two different types of UHI that directly interact with buildings and built environment. Using a multi-method approach this study proposes to analyze both SUHI and CUHI across different locations in India and the US to identify any existing correlation between them, and the factors influencing their formation. In the first method, SUHI magnitude and the factors influencing it will be estimated using remote sensing data. Though this method calculates LST at a specific time of day, it is specifically useful in drawing comparisons across cities and for correlating the urban and rural surface properties (including building roofs) with LST and SUHI formation. This method, however, is incapable of isolating the individual building systems and their influence on UHI. Thus, in the second method, this research proposes to conduct simulations using an urban canopy model (UCM) to study the sensitivity of CUHI to the factors influencing its formation. Specifically, the energy interplay between buildings and canopy UHI will be quantified. Sensitivity study of multiple factors such as heat rejection through buildings, roof albedo, wall surface properties, building material, urban density, height/width ratio that can potentially impact the outside air temperatures will be performed using a UCM. Further, SUHI analysis would be used as a basis for developing urban design-related input parameters for the UCM. Surface temperatures from the SUHI analysis will be correlated with the temperatures from CUHI simulations to identify the correlation between surface and canopy UHI, and this could further serve as a validation of the UCM used – both of which are missing in Indian context. Some of the important expected outcomes of this research are: 1.) a list of urban natural and built environment related factors that influence UHI formation, 2.) potential mitigation measures for UHI at different scales and locations, 3.) a correlation between SUHI and CUHI in Indian context, 4). a quantitative and qualitative analysis of the hotspots and cool spots across India, and 5.) a correlation between building energy use intensity and UHI magnitude. On a whole this study is expected to quantify building design changes that could mitigate UHI and what they mean in terms of building energy performance.
UHI related policy makers, and code and standard development organizations are expected to benefit from the outcome of this research. Currently, the most commonly prescribed UHI mitigation measures across the globe are increased vegetation and high roof albedos. The proposed research can validate these recommendations for different Indian locations (climate, population and biophysical characteristics) and propose more localized measures. The list of UHI mitigation measures that can be formulated from this research can be implemented as local bylaws by the policy makers and local governments. Implementation of UHI mitigation measures could have an immediate impact on indoor and outdoor comfort and air quality, and on building energy consumption. On a broader scale, UHI mitigation measures translate into reduced greenhouse gas emissions and mitigation of climate change. Further, this research is expected to be the first of its kind in the Indian context, especially through application of an urban canopy model for Indian urban regions, and for its multi-method approach of UHI analysis. As such, it will serve as a stepping stone for more such research for a country that is expected to be the biggest contributor of urban growth in next 30 years.
The complete proposal document is available here:
https://cmu.box.com/s/c8hm3357dmymny3gef5oh2cbfaxgm9y7