UHI Final Report 2017 PDF

Final Report Urban Planning Characteristics to Mitigate Climate Change in context of Urban Heat Island Effect Prepared for Environmental Management & Policy Research Institute (EMPRI) i Final Report on Urban Planning Characteristics to Mitigate Climate Change in Context of Urban Heat Island Effe...

Final Report Urban Planning Characteristics to Mitigate Climate Change in context of Urban Heat Island Effect Prepared for Environmental Management & Policy Research Institute (EMPRI) i Final Report on Urban Planning Characteristics to Mitigate Climate Change in Context of Urban Heat Island Effect © The Energy and Resources Institute 2017 Suggested format for citation T E R I. 2017 Final Report on Urban Planning Characteristics to Mitigate Climate Change in Context of Urban Heat Island Effect Bangalore : The Energy and Resources Institute. 82 pp. [Project Report No. 2016BG03] For more information The Energy and Resource Institute 4th main 2nd cross Domlur 2ndstage Bangalore – 560071 India ii Tel. 25356590 to 25356594 E-mail [email protected] Fax: 25356589 Web www.teriin.org India +91 • Bangalore (0)80 Final Report on Urban Planning Characteristics to Mitigate Climate Change in Context of Urban Heat Island Effect Project Duration August 1, 2016 to September 8, 2017 Project Team- TERI Ms. Minni Sastry (Project in Charge) Mr. Hara Kumar Varma (Co –PI) Ms. Vini Halve (Team Member) Project Support Team- EMPRI Dr. Ritu Kakkar Dr. K.H. Vinay Kumar Dr. O.K. Remadevi Dr. Papiya Roy Acknowledgements We would like to extend our sincere gratitude to Dr. Ritu Kakkar, DG- EMPRI, as well as Dr. O.K. Remadevi and Dr. Papiya Roy at EMPRI for providing us the opportunity to carry out this study. We are immensely grateful to Mr Guruprakash Sastry and Ms Amruta Parade at Infosys, Bangalore, Mr P.K. Mishra, Vice President (Planning and Procurement)-Salarpuria Sattva along with Mr Hegde at Salarpuria Sattva for helping us fetch necessary permissions for the monitoring studies. We thank the residents of Jayanagar, Basweshwar Nagar, Koramangala and HSR for their kind support during monitoring process. We also appreciate the valuable inputs provided by our colleagues in CRSBS Team, TERI Bangalore. We are also grateful to Mr J.N. Murthy, Mr P.R. Kumar and Ms Uma Maheshwari for their timely coordination in administrative and financial issues. iii Final Report on Urban Planning Characteristics to Mitigate Climate Change in Context of Urban Heat Island Effect Table of contents 1 2 EXECUTIVE SUMMARY ............................................................................................................ 1 INTRODUCTION ....................................................................................................................... 3 2.1 Objectives .......................................................................................................................... 4 2.2 Need ................................................................................................................................... 4 3 REVIEW OF LITERATURE ......................................................................................................... 5 3.1 Urban Heat Island ............................................................................................................ 5 3.2 Urban Heat Island and Climate Change....................................................................... 6 3.3 Urban Heat Island and the Built Environment ............................................................ 6 3.3.1 Green Cover ....................................................................................................... 7 3.3.2 Urban Geometry ................................................................................................ 8 3.3.3 Urban Surface Characteristics ......................................................................... 8 3.3.4 Anthropogenic Heat ......................................................................................... 9 3.4 Energy Balance of the Earth............................................................................................ 9 3.5 Surface Energy Balance of Urban and Rural Areas................................................... 10 3.6 Urban Climate Scales ..................................................................................................... 12 3.7 Types of UHI .................................................................................................................. 13 3.7.1 Surface-Urban Heat Islands ........................................................................... 13 3.7.2 Atmospheric Urban Heat Islands ................................................................. 14 3.8 Determination and Measurement Approaches ......................................................... 14 3.8.1 Thermal Remote Sensing ............................................................................... 14 3.8.2 Small Scale Modelling .................................................................................... 15 3.8.3 Field Measurements........................................................................................ 16 3.9 Essential Thermal Parameters Associated with UHI ................................................ 16 3.9.1 Air Temperature (AT)..................................................................................... 16 3.9.2 Black-Globe Temperature (GT) ..................................................................... 16 3.10 International Studies on Urban Heat Islands ...................................................... 17 3.11 Urban Heat Island Studies in India....................................................................... 18 3.12 Studies done for Bangalore .................................................................................... 22 3.13 UHI Mitigation Projects Implemented in other countries ................................. 24 4 METHODOLOGY FOR EXPERIMENTAL STUDIES ................................................................. 25 4.1.1 Activity 1: Site Selection and Study of Urban Planning Characteristics . 25 4.1.2 Activity 2: Field Measurements and Analysis ............................................ 25 4.1.3 Activity 3: Observations and Recommendations ....................................... 25 4.2 Monitoring Schedule ..................................................................................................... 26 4.3 Equipment Used for Monitoring ................................................................................. 26 5 STUDY AREA .......................................................................................................................... 28 5.1 Climate............................................................................................................................. 28 5.2 Urban Sprawl .................................................................................................................. 29 5.3 Locations Identified for Study...................................................................................... 30 5.3.1 Residential Typology (Monitoring I and II): Selection Criteria ................ 31 5.3.2 Residential Locations (Monitoring III): Selection Criteria ......................... 36 5.3.3 IT Park Typology............................................................................................. 41 6 RESIDENTIAL TYPOLOGY: RESULTS AND ANALYSIS ......................................................... 47 6.1 Monitoring I Results ...................................................................................................... 47 6.2 Monitoring II Results ..................................................................................................... 49 6.3 Observations from Monitoring I and II ...................................................................... 52 6.4 Monitoring III Results ................................................................................................... 53 6.5 Observations from Monitoring III ............................................................................... 55 7 IT-OFFICE TYPOLOGY: RESULTS AND OBSERVATIONS ..................................................... 57 7.1 Results.............................................................................................................................. 57 7.2 Observations ................................................................................................................... 59 8 RESULTS OF INFRA-RED THERMAL IMAGING .................................................................... 60 9 CONCLUSIONS AND RECOMMENDATIONS ........................................................................ 62 10 WAY FORWARD ..................................................................................................................... 67 11 BIBLIOGRAPHY ...................................................................................................................... 68 12 ANNEXURES ........................................................................................................................... 70 iv Final Report on Urban Planning Characteristics to Mitigate Climate Change in Context of Urban Heat Island Effect List of Tables Table 3-1 Characteristics of Surface and Atmospheric Urban Heat Islands (3) 14 Table 3-2 A review of various UHI Studies carried out in different cities of India 19 Table 4-1 Monitoring Schedule 26 Table 4-2 Monitoring Equipment 27 Table 5-1 Monthly Temperature and Humidity data (Bangalore Climatological Table 1971– 2000). 28 Table 5-2 Summary of residential locations selected for Monitoring I and II 35 Table 5-3 Summary of residential locations selected for Monitoring III 40 Table 5-4 Summary of IT locations selected for monitoring 46 List of Figures Figure 1-1 Satellite Image of Bangalore showing different locations selected for the study (Map Source: Google Maps)....................................................................................................... 1 Figure 3-1 Variations of Surface and Air Temperatures in different types of urban areas compared to rural peripheries. (3) ............................................................................................ 5 Figure 3-2 UHI Mitigation Approaches ............................................................................................ 7 Figure 3-3 How green cover influences formation of UHI (9) ....................................................... 7 Figure 3-4 Formation of ‘Urban Canyons’ based on different heights and widths of urban masses, and their effect on the canyon temperature (10) ...................................................... 8 Figure 3-5 A schematic diagram given by NASA shows the balance between incoming and outgoing energy of the earth (11) ............................................................................................ 10 Figure 3-6 Radiation and energy exchanges in urban and rural built environments on a clear day. (14). .................................................................................................................................... 11 Figure 3-7 Urban built environment and wind behavior. (6) ...................................................... 12 Figure 3-8 Radiation fluxes and effect of urban canyons (3)........................................................ 12 Figure 3-9 Urban Climate Scales (15) .............................................................................................. 13 Figure 3-10 Thermal Image of a city showing temperature of different surfaces. (7) .............. 15 Figure 3-11 Increasing Built-up area from 1973 to 2009 (32)........................................................ 22 Figure 3-12 Increased Land Surface Temperatures in 1992, 2002 and 2007 (32) ....................... 23 Figure 3-13 Land Surface Temperatures in Bangalore as observed on March 2003. (33) ........ 23 Figure 4-1 Heat Stress Meter assembly and mounting ................................................................. 27 Figure 4-2 Heat Stress Meter Figure 4-3 Infra-red thermal camera ........................................ 27 Figure 5-1 Location of Bangalore in the Indian subcontinent...................................................... 28 Figure 5-2 Monthly average rainfall in Bangalore Figure 5-3 Monthly average direct solar-radiation received in Bangalore..................................................................................... 29 Figure 5-4 Growing population of Bangalore from 1871 to 2007 (Source: Census of India) ... 29 Figure 5-5 Growing area of the city from 1949 to present. (Source: Census of India) .............. 29 Figure 5-6 Temperature Trend of Bangalore from 1940 to 2017. (35) ......................................... 30 Figure 5-7 Satellite Image of Bangalore showing different locations selected for the study (Map Source: Google Maps)..................................................................................................... 31 Figure 5-8: Urban Characteristics of Location I: Lalbagh (Jayanagar IV Block) ........................ 32 Figure 5-9 Urban Characteristics of Residential Location II: Basweshwar nagar ..................... 33 Figure 5-10 Urban Characteristics of residential location III: Bellandur .................................... 34 Figure 5-11 Urban Characteristics of Location selected at Koramangala .................................. 37 v Final Report on Urban Planning Characteristics to Mitigate Climate Change in Context of Urban Heat Island Effect Figure 5-12 Urban Characteristics of Location selected at HSR Layout ..................................... 38 Figure 5-13 Urban Characteristics of Location selected at Jayanagar I Block ........................... 39 Figure 5-14 Urban Characteristics of Location Selected at Electronics City .............................. 42 Figure 5-15 Urban Characteristics of Location selected at Marathahalli ................................... 44 Figure 5-16 Urban Characteristics of Location selected at Whitefield........................................ 45 Figure 6-1 Hourly averages of air temperature (AT), globe temperature (GT), wet-bulb temperature (WBT) and relative humidity (RH) for Residential location-1: Lalbagh ..... 47 Figure 6-2 Hourly averages of air temperature (AT), globe temperature (GT), wet-bulb temperature (WBT) and relative humidity (RH) for Residential location-2: Basweshwar Nagar........................................................................................................................................... 48 Figure 6-3 Hourly averages of air temperature (AT), globe temperature (GT), wet-bulb temperature (WBT) and relative humidity (RH) for Residential location-3: Bellandur .. 48 Figure 6-4 Monitoring I Results (Residential locations)- Comparison of AT and RH ............. 49 Figure 6-5 Monitoring I Results (Residential locations)- Comparison of GT ............................ 49 Figure 6-6 Hourly averages of air temperature (AT), globe temperature (GT) and relative humidity (RH) for Residential location-1: Lalbagh. (Monitoring Period: 15-March-2017 to 22-March-2017) ...................................................................................................................... 50 Figure 6-7 Hourly averages of air temperature (AT), globe temperature (GT) and relative humidity (RH) for Residential location-2: Basweshwar Nagar. (Monitoring Period: 15March-2017 to 22-March-2017) ................................................................................................ 50 Figure 6-8 The narrow street canyon at Bellandur ........................................................................ 51 Figure 6-9 Hourly averages of air temperature (AT), globe temperature (GT) and relative humidity (RH) for Residential location-3: Bellandur. (Monitoring Period: 15-March2017 to 22-March-2017) ............................................................................................................. 51 Figure 6-10 Monitoring II Results (Residential locations)- Comparison of AT and RH .......... 52 Figure 6-11 Monitoring II Results (Residential locations)- Comparison of GT ......................... 52 Figure 6-12 Hourly averages of air temperature (AT), globe temperature (GT) and relative humidity (RH) for Residential location-4: Jayanagar I Block. (Monitoring Period: 31 May 2017 to 10 Jun 2017). ......................................................................................................... 53 Figure 6-13 Hourly averages of air temperature (AT), globe temperature (GT) and relative humidity (RH) for Residential location-5: Koramangala. (Monitoring Period: 31 May 2017 to 10 Jun 2017). .................................................................................................................. 53 Figure 6-14 Hourly averages of air temperature (AT), globe temperature (GT) and relative humidity (RH) for Residential location-6: HSR Layout. (Monitoring Period: 31 May 2017 to 10 Jun 2017). .................................................................................................................. 54 Figure 6-15 Comparative Analysis of Hourly averages of air temperature (AT)and relative humidity (RH) for Residential location- Monitoring III. (Monitoring Period: 31 May 2017 to 10 Jun 2017). .................................................................................................................. 54 Figure 6-16 Comparative Analysis of Hourly averages of Globe Temperature (GT) for Residential location- Monitoring III. (Monitoring Period: 31 May 2017 to 10 Jun 2017). 55 Figure 7-1 Hourly averages of air temperature (AT), globe temperature (GT), wet-bulb temperature (WBT) and relative humidity (RH) for IT-1: Electronic City. (Monitoring Period: 15-March-2017 to 22-March-2017) ............................................................................. 57 Figure 7-2 Hourly averages of air temperature (AT), globe temperature (GT), wet-bulb temperature (WBT) and relative humidity (RH) for IT-2: Marathahalli. (Monitoring Period: 15-March-2017 to 22-March-2017) ............................................................................. 57 vi Final Report on Urban Planning Characteristics to Mitigate Climate Change in Context of Urban Heat Island Effect Figure 7-3 Hourly averages of air temperature (AT), globe temperature (GT), wet-bulb temperature (WBT) and relative humidity (RH) for IT-3: Whitefield. (Monitoring Period: 15-March-2017 to 22-March-2017). ............................................................................ 58 Figure 7-4 Comparative Analysis of Hourly averages of Air Temperatures (AT) and Relative Humidity (RH) for IT Locations. (Monitoring Period: 15-March-2017 to 22-March-2017). ...................................................................................................................................................... 58 Figure 7-5 Comparative Analysis of Hourly averages of Globe Temperatures (GT) for IT Locations. (Monitoring Period: 15-March-2017 to 22-March-2017). ................................... 59 Figure 8-1 Street Canyon at Marathahalli IT Park ........................................................................ 60 Figure 8-2 An un-shaded street with low H/W ratio and low green cover ............................... 60 Figure 8-3 A street shaded due to tall buildings and trees ......................................................... 60 Figure 8-4 A fully shaded street at Lalbagh: The street is shaded almost throughout the day because of the dense canopy cover ......................................................................................... 61 Figure 9-1 A example of a narrow north-south oriented street ................................................... 65 Figure 9-2 An example of a wide East-West oriented street ........................................................ 66 List of Abbreviations UHI - Urban Heat Island IPCC - Intergovernmental Panel on Climate Change EPA- Environmental Protection Agency GHG- Green House Gases UCL - Urban canopy layer RSL - Roughness sub-layer ISL - Inertial sub-layer H/W – Height/Width AT - Air Temperature GT - Globe Temperature MRT – Mean Radiant Temperature PET – Physiological Equivalent Temperature SVF - Sky-View Factor HXG – Height/Width x Green Cover GIS – Geographic Information System NDVI – Normalized Difference Vegetation Index TM – Thematic Mapper (Landsat) RH – Relative Humidity IR - Infra-Red vii Final Report on Urban Planning Characteristics to Mitigate Climate Change in Context of Urban Heat Island Effect 1 Executive Summary In the last few decades, cities around the world have seen significant urbanization, marked by the increase in building infrastructure and automobiles. Permeable land surfaces which were once covered by vegetation have now been replaced with impermeable and high emissivity surfaces and mostly un-shaded. Such urban surfaces tend to absorb the solar radiation and emit it later, which causes an increase in local temperatures. Consequently, the urban areas observing higher temperatures become ‘’heat islands’’, compared to their rural counterpart. In a study carried out by TERI in 2014, it was found that Bangalore is one such example of a city where dense urban pockets were found to be about 2 ᵒC warmer than nearby rural area (1). In another study done by IISC, an increase of 2-2.5ᵒC was observed during the last decade owing to 76% decline in vegetation cover and 79% decline in water bodies, which is indisputably due to reckless urban sprawl. (2). Urban Heat Islands (UHI) can cause deterioration of living environment, elevation of ground level ozone, health disorders and increase in building energy consumptions. Thus the aim of the project includes assessing the impact of urban planning aspects of urban geometry and green cover on the formation of UHI within different zones of Bangalore. The study therefore helped in developing relationship between planning characters and microclimatic influence which will be useful for urban planners to mitigate UHI in newly developing areas of the city. The building typologies were considered to be residential and commercial (IT or Information Technology) as they are predominant in Bangalore. Three locations were strategically selected for each monitoring based on various urban characteristics such as green cover, open lands, water bodies, height to width (H/W) ratios etc. Continuous monitoring of thermal parameters such as air temperature (AT), globe temperature (GT) and relative humidity (RH) was carried simultaneously in these selected locations. Figure 1-1 Satellite Image of Bangalore showing different locations selected for the study (Map Source: Google Maps) 1 Final Report on Urban Planning Characteristics to Mitigate Climate Change in Context of Urban Heat Island Effect For residential typology, two monitorings were conducted in three locations: Bellandur, Lalbagh and Basweshwar Nagar areas. The results indicate Basweshwar Nagar recorded highest GT and AT with lowest RH out of all three locations due its lowest green cover, higher H/W ratio, high density and absence of open lands and water bodies. Bellandur although has comparatively higher H/W ratio like in Basweshwar Nagar and low green cover yet recorded lower temperatures due to the mutual shading of buildings and high RH which is because of its close proximity to a large water body. Lalbagh readings also represent similar or slightly lower UHI effect than Bellandur. This is because of its highest green cover out of all three locations including small percentage of open lands and a water body. Therefore it can be concluded that green cover and water bodies with open lands help in reducing temperatures. Locations with higher H/W ratio would not be very effective without sufficient green cover. From the first monitoring, some errors were observed due to which a second monitoring was performed for same locations during the summer. From both monitorings, impact of H/W ratio was determinable but effectiveness of green cover against open lands and water bodies could not be ascertained. Hence a third monitoring was performed for three different locations: Koramangala, Jayanagara and HSR layout. From the third monitored readings, Koramangala showed best performance which has thick green cover as well as open lands with huge water body. HSR layout on other hand has the similar proximity to the open lands and water body as Koramangala but green cover is less. HSR location however recorded better thermal performance than Jayanagar which has thick green cover but less open lands and water bodies. This explains that water body and open lands have greater impact in mitigating UHI effect than green cover. For commercial/IT typology, three locations were selected for monitoring: Electronic City, Marathahalli and Whitefield. Data from Marathahalli showed lowest GT and AT during daytime, despite having identical RH, in comparison to other locations. This is because of the high H/W ratio. On the other hand Whitefield recorded highest GT and AT during daytime and high diurnal variation due to large and exposed open lands. Electronic city recorded lowest during night and slightly higher than Marathahalli. This is due to its thick green cover and high reflective surface finishing on building enevelops. The comparative analysis could be understood as high H/W ratio, green cover and water bodies can help reducing the local temperatures. To sum up, analysis of the results helped establishing a relation between the urban characteristics of the locations and their thermal environment. 2 Final Report on Urban Planning Characteristics to Mitigate Climate Change in Context of Urban Heat Island Effect 2 Introduction Urban Heat Island (UHI) is being experienced in developing cities of developing countries, and it is predicted that the magnitude of Urban Heat Island will further intensify with high rise-high density development. As per United States Environmental Protection Agency ‚As urban areas develop, changes occur in their landscape. Buildings, roads, and other infrastructure replace open land and vegetation that were once permeable and moist become impermeable and dry. These changes cause urban regions to become warmer than their rural surroundings, forming an "island" of higher temperatures in the landscape‛ (1). Urban structure of a city which includes, land use planning, building morphology, surface characters along with the anthropogenic heat which is generated from vehicles and equipment such as air conditioners are the most crucial factors causing increase in air temperature or urban heat island. These in turn increase air pollution and also energy consumption of buildings in providing thermal comfort inside the buildings by use of refrigeration. This eventually leads to an increase of greenhouse gas emissions and negative impacts on health of citizens of developing cities. IPCC (Intergovernmental Panel on Climate Change) 2014, had one chapter dedicated on UHI. The report recognizes the presence of UHI due to urban densification, reduction in vegetation cover, and increase in anthropogenic heat. UHI mitigation strategies are seen necessary in order to reduce GHG emissions from urban areas. In context to the above, it is important that State Governments and urban planning agencies are equipped with tools, guidelines and understanding of impact of buildings and urbanization on climate of the city. The overall objective of the exercise is to look at urban planning as a tool to make urban centres more manageable and liveable. The focus is on Bangalore city, as the city has gone through rapid urbanization in the last few decades. Bangalore is classified as the third most populous city of India, after Mumbai and Delhi, with a population hitting about 11.5 Million in 2016. Rapid urbanization has seen many negative environmental impacts on the city, which include, diminishing lakes, traffic congestions along with high air pollution levels, urban flooding during heavy rains and increase in summer temperatures. In the summer of 2016, highest air temperature recorded in Bangalore was 39ᵒC. All the above environmental impacts are related to Urban Heat Island effect, which is mostly related to the manner urban development takes place. If the current scenario continues, Bangalore could lose its charm of enjoying the salubrious temperate/moderate weather conditions. Thus, in this project, it is planned to study the effect of urban characteristics on UHI by recording temperatures at strategically identified locations, along with the documentation of physical characteristics of urban planning and anthropogenic heat being emitted in the locations. Based upon the monitored results relation between urban planning characteristics and UHI will be framed. This will provide with important guidelines for urban planners, while carrying out urban planning for new locations/satellite towns around Bangalore. 3 Final Report on Urban Planning Characteristics to Mitigate Climate Change in Context of Urban Heat Island Effect 2.1 Objectives To study the Urban Heat Island effect within different pockets of Bangalore with respect to urban planning and develop relation between planning characteristics and microclimate, which will be useful for urban planners/authorities to mitigate UHI and climate change in newly developing areas of Bangalore. 2.2 Need Urban heat islands can cause deterioration of living environment, increase in energy consumption, elevation in ground-level ozone, and even an increase in mortality rates. In a research by Konopacki and Akbari, it was observed that by mitigating UHI effects in Houston, it was possible to achieve savings of 82 million USD with a reduction of 730MW peak power, leading to an annual decrease of 170000 tonnes of carbon emission. (2). In context of Bangalore, implementing white roofs alone can reduce energy consumption by 1642 MWh/Sqm/yr, which would result in savings of Rs. 10,348 million per year. (3). In 1998, it was reported that the ozone level could exceed 120 ppbv at 22ᵒC, and could reach 240 ppbv at 32ᵒC. Hence, annual reduction of 25GW of electrical power or potential savings of USD 5 billion by year 2015 can be predicted. It is apparent that the benefits of mitigation of UHI are vast, and particularly for a developing tropical country like India, study in this field can bring about timely intervention in urban policies to result in energy savings and outdoor thermal comfort. 4 Final Report on Urban Planning Characteristics to Mitigate Climate Change in Context of Urban Heat Island Effect 3 Review of Literature 3.1 Urban Heat Island An Urban Heat Island has been best described as a dome of stagnant warm air over the heavily built-up areas of the city (4). Due to this phenomenon, many urban and suburban areas experience a higher temperature than the surrounding rural areas as seen in Figure 3-1. This difference in temperature can be as high as 1 to 3ᵒC for a city with about 1 million people; while on a clear calm night, the difference can be as much as 12ᵒC (1). In New Delhi, the summer time temperature was recorded to be 7-10 ᵒC higher than the temperature of surrounding rural areas. Figure 3-1 Variations of Surface and Air Temperatures in different types of urban areas compared to rural peripheries. (1) It is estimated that for every 0.6°C rise in temperature, there is an increase in electricity consumption of about 2%. (5). Increase in thermal discomfort has led to increase in use of air conditioning appliances, resulting in increased emission of harmful greenhouse gasses which has led to global climate change. Harmful gasses released from power plants cause further increase the air pollution, and in due course, intensify the UHI. Besides affecting air quality, the surface UHI can also affect water quality, as the temperature of run-off storm water increases after flowing over heated pavements and urban surfaces. When this heated storm water flows into water bodies, it tends to disturb the balance of aquatic ecosystems. In a study carried out in American cities of Atlanta, Dallas, San Antonio and Nashville, NASA researchers have found that urban areas with high concentrations of buildings, roads and other artificial surfaces retain heat and lead to warmer surrounding temperatures. During summer months, the rising heated air creates wind circulation and enhances cloud formation and rainfall. (6) 5 Final Report on Urban Planning Characteristics to Mitigate Climate Change in Context of Urban Heat Island Effect In areas with tropical climate, increased atmospheric heat can lead to several health hazards such as heat strokes, exhaustion and respiratory problem among the population. In densely urban areas, the suspended and highly flammable particles accumulated in the air, combined with the rise in temperature can trigger fires. In summers, dry trees and vegetation can also catch fire. (7) The undesirable effects of urban heat islands can be summarized as: 1. Increased heat transfer indoor leading to increased electricity consumption for cooling in tropical countries. 2. Thermal discomfort (both indoor and outdoor) leading to health hazards 3. Increased rainfall intensities over urban areas 4. Increased emission of greenhouse gasses leading to global climate change 5. Risk of fire breakouts Thus, in the developing countries having tropical climate, the issue of urban heat island has become critical, and is predicted to increase significantly in the near future. With increasing severity of the problem, vast research is being dedicated to this subject and sufficient literature is available. 3.2 Urban Heat Island and Climate Change The effect of Urban Heat Island on Climate change is two-fold. Firstly, the heat build-up caused by urban heat island effect can worsen the effect of global warming in affected urban areas. As the result, these areas may experience more severe heat-waves with very high daytime summer temperature. Secondly, the increased heat gains in conditioned buildings caused by the heat build-up leads to increased electricity demand for cooling. As developing countries are predominantly dependent on conventional1 methods of energy generation, the increased electricity demand can cause surge in the rate at which greenhouse gases are released into the atmosphere. For developing countries having limited natural resources and a developing economy, the increased demand of electricity may also lead to economic stress. Hence employing strategies to mitigate UHI can benefit tropical countries in the mitigation of climate change. 3.3 Urban Heat Island and the Built Environment Urbanization has led to rampant deforestation and construction activities in urban areas. The reduction in urban green cover and the increase of built-up hard surfaces as well as emissions are primary causes of urban heat islands. Thus UHI mitigation strategies should aim to restrict the excessive heat built up by: 1. Reduction of use of hard and absorptive surfaces, 2. By providing sufficient shading from solar radiation and 3. Reducing anthropogenic GHG emissions. (See Figure 3-2). 1Conventional methods of energy generation refer to those that depend on non-renewable sources of energy and also cause considerable emissions. 6 Final Report on Urban Planning Characteristics to Mitigate Climate Change in Context of Urban Heat Island Effect Figure 3-2 UHI Mitigation Approaches 3.3.1 Green Cover Trees reduce temperature by means of shading and evapotranspiration. With reducing green cover, there is less shading, hence exposed surface tend to absorb more heat which is later dissipated into the air. With reduced evaporation, the moisture required to cool down the air is not available, hence the air temperature remains increased. Urban paved surfaces consist of upto 75% impervious surfaces, whereas natural ground cover is about 10% impervious, hence natural ground surface can provide sufficient moisture for cooling the air near the surface. (Figure 3-3) Figure 3-3 How green cover influences formation of UHI (8) 7 Final Report on Urban Planning Characteristics to Mitigate Climate Change in Context of Urban Heat Island Effect 3.3.2 Urban Geometry Urban geometry deals with the dimensions of the built environment for a given urban area. It may directly influence wind movement, shading patterns, heat absorption and the ability of a surface to emit long-wave radiation back to the space. (1). The effect or UHI is particularly distinct in urban canyons, which are urban enclosures formed by narrow streets and tall building on both sides. On one hand, during the daytime, the tall buildings can shade the canyon reducing surface temperature, but on the other hand the surfaces of these tall buildings may reflect and absorb the heat leading to increased air temperatures. (See Figure 3-4). Figure 3-4 Formation of ‘Urban Canyons’ based on different heights and widths of urban masses, and their effect on the canyon temperature (9) 3.3.3 Urban Surface Characteristics Urban surfaces absorb, reflect and re-emit solar energy, thus their characteristics such as thermal capacity, emittance, thermal absorbance and reflectance significantly affect UHI formation. Urban areas generally exhibit low-albedo surfaces such as roads, rooftops and pavements, which are less capable of reflecting solar heat, compared to rural areas. Hence urban surfaces absorb a lot of heat leading to increased surface temperatures and consequently formation of surface UHI. Thermal capacity of a material governs the amount of heat that the material can store. Urban surfaces built with materials such as steel and cement are capable of storing more heat compared to rural surfaces such as soil and sand, therefore core urban areas tend to have absorbed more heat than its outskirts, this heat is then emitted back at nights. Due to this phenomenon, diurnal variations are very low in UHI affected urban areas when compared to rural cases. With interventions such as reflective roofs and green roofs, a reduction of 1.5ᵒC and 1.9ᵒC can be observed, which can facilitate savings of 16.9% and 11.8% respectively. (3). 8 Final Report on Urban Planning Characteristics to Mitigate Climate Change in Context of Urban Heat Island Effect 3.3.4 Anthropogenic Heat Heat caused due to human activity such as manufacturing, heating or cooling, lighting, transportation, heat from human and animal metabolism together constitute the anthropogenic heat, which eventually leads to increased UHI. Urban settings comprise of more energy-intensive buildings that contribute more anthropogenic heat to its surroundings. Urban climate is associated with the heat and moisture emitted by cities in association with energy consumption of cities. Sensible anthropogenic heat emission into the atmosphere can be directly from chimneys, air conditioners, heaters etc and indirectly from building envelope through convection and radiation into the urban environment. The defined sectors which contribute to the anthropogenic heat generation are: transport, building, industry and human metabolism. The cooling system of buildings consumes energy to reject heat of the building into the urban environment. This rejected heat can be quantified as: R = E+P+M+L+AC E-Heat transmitted in building from external environment P-Plug Loads M-Human Metabolism L-Heat generated by lighting AC-additional energy consumed by cooling systems Some air conditioning systems use evaporative cooling to exchange heat with the outside environment. In such cases, majority of heat is removed in form of evaporated water. The largest fraction of anthropogenic heat from buildings comes in the form of heat and moisture rejected by the building through its mechanical heating, cooling and ventilation systems. Data from earlier studies show, city wise anthropogenic heat emissions can vary from 15-150W/m2. (David J. Sailor). In an urban context, vehicles emit enough heat to considerably add to the increasing heat island intensity. In a research conducted in Beijing, it was found that conventional vehicles would emit 9.85 x 1014 J of heat energy per day. And upon replacing conventional vehicles by electrical vehicles, the heat emitted would reduce by 7.9x 1014 J. 3.4 Energy Balance of the Earth The Intergovernmental Panel on Climate Change (IPCC) defines ‚Energy Balance‛ of the Earth as the difference between total incoming and outgoing energy. If the balance is positive, warming occurs, and if it is negative, cooling occurs. When averaged over the globe and over long periods of time, this balance must be zero. 9 Final Report on Urban Planning Characteristics to Mitigate Climate Change in Context of Urban Heat Island Effect Given that the earth receives all its energy from the sun, the zero balance implies that : Global incoming solar radiation – Reflected solar radiation (from the top of the atmosphere) - Outgoing long-wave radiation (emitted by the earth surface)= 0 Figure 3-5 A schematic diagram given by NASA shows the balance between incoming and outgoing energy of the earth (10) The earth loses most of its accumulated heat in the form of outgoing long wave radiation, This is the natural cooling mechanism which the earth uses to sustain zero energy balance. The local differences between the radiative heating and cooling provide the energy that drives atmospheric dynamics. The outgoing long-wave radiation component is thus of prime importance when the dynamics of UHI are concerned. (Figure 3-5) The ‚energy balance‛ equation suggested by Oke explains the interactions between anthropogenic heat and the environment: Net radiation + anthropogenic heat = Latent heat flux + sensible heat flux + storage heat flux + net heat advection Where, Net radiation = Net diffuse short-wave radiation + Net direct short-wave radiation + Net long-wave radiation 3.5 Surface Energy Balance of Urban and Rural Areas The urban built environment interacts with the urban climate in many ways. The fluxes of heat, moisture and momentum are significantly altered by the urban landscape. Also, the anthropogenic input of pollutants in the urban atmosphere changes the net allwave radiation budget by reducing the incident flux of short-wave solar radiation, by re10 Final Report on Urban Planning Characteristics to Mitigate Climate Change in Context of Urban Heat Island Effect emitting long-wave radiation to the urban surfaces, and by absorbing long-wave radiation from the urban heated urban surfaces which then warms up the air. (11) The predominant impervious surfaces in an urban built environment do not absorb rainwater and remain dry. This leads to evaporation deficit in the city. However in rural areas, the natural surfaces retain water and remain moist. These moist surfaces allow evaporative cooling by enhancing the latent heat flux. (12) These exchanges can be seen in Figure 3-6. Figure 3-6 Radiation and energy exchanges in urban and rural built environments on a clear day. (13). Urban fabric consisting of materials such as concrete, asphalt and stone has a high thermal capacity and low albedo compared to predominant rural surfaces such as soil and vegetation. Because of this, the urban surfaces absorb a high percentage of short-wave solar radiation and dissipate it to the ambient air in the form of long wave radiation at night. This phenomenon causes higher night-time air temperature in cities in contrast with rural environments that rapidly cool down. The roughness of an urban surface is made up by vertical urban geometry. This roughness of the urban fabric provides undesirable friction to the horizontal air flow through the urban environment. This causes the formation of a stagnant cloud of warm air in the urban canopies. (Figure 3-7) 11 Final Report on Urban Planning Characteristics to Mitigate Climate Change in Context of Urban Heat Island Effect Figure 3-7 Urban built environment and wind behavior. (5) The enclosures formed by tall buildings and streets, known as urban canyons can behave as radiation traps (Figure 3-8). During the day, the canyon surfaces continuously absorb shortwave radiation from the sun and release it slowly to the sky as long wave radiation during the night. Where the canyons are tall and the sky-view factor is less, most of the long-wave radiation remains trapped in the canyon below the canopy level, causing an increase in the urban heat island effect. Figure 3-8 Radiation fluxes and effect of urban canyons (1) 3.6 Urban Climate Scales Oke in 2006 suggested that the urban processes of heat transfer occur differently at different urban scales namely Micro, Local and Meso (Figure 3-9). At micro scale, the roughness layer comprises of ‚urban canopy layer‛ (UCL). It is the layer where main roughness elements such as buildings and trees exist. It is at this layer that the exchanges of heat and moisture with the built form occur. Typically the height of UCL is equal to the mean height of roughness elements of the given urban area. As the microclimatic effects of individual surfaces blend by turbulence the roughness sub-layer (RSL) is formed. The height of RSL may be as less as 1.5x height of UCL (for dense urban 12 Final Report on Urban Planning Characteristics to Mitigate Climate Change in Context of Urban Heat Island Effect areas) and upto 4x height of UCL (for low-density areas). Instruments located in RSL measure a blended, spatially averaged signal representative of the local scale. Hence, while carrying out measurements at RSL, the individual sources of the heat fluxes are difficult to identify. At local scale, the surface layer comprises of roughness sub-layer and inertial sub-layer (ISL). Inertial sub-layer is where the atmosphere adjusts to the underlying urban landscape such that the observations of energy, mass and momentum fluxes made at this height are representatives of the amalgam of microclimates created by the urban landscape. At meso scale, the mixed layer above is where the urban surface exchanges blend together with the wider atmosphere and is then transported downwind in the form of ‚urban plume‛, seen in Figure 3-7. Figure 3-9 Urban Climate Scales (14) 3.7 Types of UHI On the basis of its impacts, the urban heat island effect can be of two types: Surface UHI and Atmospheric UHI. 3.7.1 Surface-Urban Heat Islands These are caused when the heat from solar radiation is absorbed by dry and exposed surfaces of the urban set-up. Its magnitude is thus dependent on the intensity of solar radiation, which changes seasonally and diurnally. This is why Surface Urban Heat Islands are highest during summers, especially during the day-time. Another reason why summers characterize high Surface UHI is that: in summers, due to prevalent clear-sky conditions, the 13 Final Report on Urban Planning Characteristics to Mitigate Climate Change in Context of Urban Heat Island Effect solar radiation remains undispersed. Also, the days are calm, with low wind speeds, because of which the mixing of air is minimized. 3.7.2 Atmospheric Urban Heat Islands These are formed where there is a difference between the air temperatures of urban and rural areas. These are further sub-dived into two types: 3.7.2.1 Canopy Layer UHI They occur close to the ground surface, where people and built environment exists, that is from the ground surface to the topmost level of trees and roofs. 3.7.2.2 Boundary Layer UHI They occur at a level starting from the rooftops and tree tops, until the point where urban landscapes no longer affect the atmosphere. Table 3-1 gives a comparison of the two types of Urban Heat Islands. Table 3-1 Characteristics of Surface and Atmospheric Urban Heat Islands (1) Feature Temporal Development Peak Intensity Surface UHI Atmospheric UHI Present at all times of the day and night May be small or non-existent during the day Most intense during the day and in the summer Most intense at night or predawn and in the winter More spatial and temporal variation: Less variation: Day: 10 to 15°C Day: 1 to 3°C Night: 7 to 12°C Night: 5 to 10°C Typical Identification Remote Sensing (Indirect method Measurement) Through fixed weather stations or mobile traverses Surface UHI may indirectly affect Canopy Layer UHI, when the heat absorbed by urban surfaces throughout the day gets slowly released to the atmosphere at the end of the day, thus adding to the temperature of the air near the surface. 3.8 Determination and Measurement Approaches The process of measurement and monitoring of UHI is done depending upon the type of UHI. Surface UHI requires measurement of surface temperature for a given area, while atmospheric UHI requires the measurement of air temperature, as described below: 3.8.1 Thermal Remote Sensing Surface Heat islands can be studied using remote sensing techniques. Remote sensing enables us to map the pattern of urban heat island (Surface UHI) for an entire city or region. 14 Final Report on Urban Planning Characteristics to Mitigate Climate Change in Context of Urban Heat Island Effect Infra-red imagery of a geographical location is provided by satellites such as LANDSAT, or by images captures from thermal cameras mounted on aircrafts made to fly over the given city. In these infra-red images as shown in Figure 3-10, the bright coloured areas indicate hotter surfaces like roads and rooftops, while darker colours indicate cooler surfaces such as green cover, and water bodies. Remote sensing allows us to carry out a temperature study of a large area. (15) Remote sensing for UHI measurements also has certain limitations. Firstly, they do not capture thermal imagery of vertical surfaces such as external walls of the buildings, Secondly; remotely sensed data represent radiation that has travelled through the atmosphere twice, as wavelengths travel from the sun to the earth as well as from the earth to the atmosphere. Thus, the data must be corrected to accurately estimate surface properties including solar reflectance and temperature. (1) This method is also very expensive and it is very difficult to obtain steady images of the urban surface due to several factors such as atmospheric interactions and operation capability of the apparatus used. The main disadvantage of this approach is that the remote sensors only capture the upward thermal irradiance patterns, which means that the observed surface temperatures may be significantly different compared to the actual air temperatures inside the urban canopy. Figure 3-10 Thermal Image of a city showing temperature of different surfaces. (6) 3.8.2 Small Scale Modelling A prototype of the urban area is prepared as a small scale model. The prototype is tested using devices such as wind tunnels or in outdoors. Small scale modelling is used in most UHI studies to verify, calibrate and improve mathematical models. Similarity between the model and prototype is necessary to achieve accurate results. However the main drawbacks are the cost and the difficulty of experimentally generating a thermal stratification which resembles the actual atmosphere. (16) 15 Final Report on Urban Planning Characteristics to Mitigate Climate Change in Context of Urban Heat Island Effect 3.8.3 Field Measurements For a study carried over a smaller geographical area, direct measurements can be more convenient and relevant. In this approach the near surface temperature patterns in urban areas are measured and compared against surrounding rural areas Instruments may be used as fixed or mobile stations. The first study of this kind was carried out by Howard in 1818 for London city. This approach also has some limitations. Firstly the development and installation of measurement devices around a city is a very expensive and time consuming task. Secondly, through this type of approach, only limited number of parameters can be simultaneously measured, thus it is very difficult to demonstrate the three dimensional spatial distribution of quantities inside an urban area. It also becomes necessary to carry out the measurements for a long period of time, so that the effect of unpredicted factors can be cancelled out. (16) Transect Studies Transect studies involves continuous measurement of air temperature on a moving vehicle mounted with a weather station. The transect usually comprises of urban and rural areas or areas with different land-use characteristics. They provide high temporal resolution of data and cost effective. Melhuish and Pedder were the first to use and demonstrate this approach using a bicycle in Berkshire in 1998. (17) The results of such studies are mostly used to find the spatial distribution and intensity of UHI. In this study, with a similar aim, instruments with data logging capability will be fixed at several locations across Bangalore City inside the Urban Canopy Layer (UCL) with the objective of analysis of spatial and temporal atmospheric UHI in the respective locations. 3.9 Essential Thermal Parameters Associated with UHI 3.9.1 Air Temperature (AT) The dry bulb temperature is a direct indicator of ‚atmospheric‛ UHI Intensity. When measured throughout the day, highest air temperatures are usually recorded during the night in UHI affected areas against the rural. Measured air temperatures may also indicate the effect of warming occurring due to anthropogenic sources such as vehicular exhaust, air conditioning and refrigeration equipment etc. Hence industrial and commercial locations may show higher air temperatures compared to residential locations during daytime. It can be measured using a thermometer which is directly exposed to the air but shielded from solar radiation. Field campaigns, transect studies usually involve the measurement of air temperatures at different locations. In this study, hourly measurements of air temperature are taken for 7 days for selected locations based on different land—use and urban characteristics, using a data logger with air temperature sensor. 3.9.2 Black-Globe Temperature (GT) In urban locations the perceived heat is a combined effect of both air temperature and re radiated heat which comes through building surfaces. Hence, Globe Temperature as an indicator is used to measure Heat Islands. 16 Final Report on Urban Planning Characteristics to Mitigate Climate Change in Context of Urban Heat Island Effect In this study, the black globe temperature is measured as an indicator of the relative temperature of different urban surfaces in a street canyon. Hard impervious surfaces such as asphalt roads, stone pavements may reach to temperatures as high as 80 ᵒC during hot summer days. Street canyons formed by such materials absorb more heat which is then slowly dissipated through the night. The globe temperature in such street canyons is higher than others. Similarly, a street canyon which is shaded by trees will have low surface temperatures and hence low globe temperatures. A standard globe thermometer was introduced in 1930 by Vernon. It consists of a hollow copper sphere of diameter of 150mm, painted black matt, with a temperature sensor at the centre. 3.10 International Studies on Urban Heat Islands The study of urban heat islands started receiving profound attention as early as the 18th century. Luke Howard was the first to document this phenomenon in around 1818. His documentation was based on the artificial excess heat building up in the city, compared to its surroundings. Similar studies were carried out by Emilien Renou for the city of Paris during the late 19th century, followed by study of heat islands in Vienna carried out by Schmidt in 1917. This was the first study carried out using instruments mounted on motorized vehicles. Recent studies have employed several modern technologies such as mobile traverses, thermal imagery through satellites and aircrafts, and use of sophisticated instruments. Various approaches have been use in for the identification of heat islands. These indicators generally depend on the type of UHI to be studied. In a study done in Fez, Morocco, the old city with narrow pedestrian routes is compared against newly developed part, with wider roads for motor vehicles. In both areas, measurement site were chosen such that they represent different urban geometry (in terms of H/W ratio) and street orientation. Two types of urban canyon are identified: a ‚deep‛ canyon with a high H/W ratio, and a ‚shallow‛ canyon with a lower H/W ratio. Continuous measurements were taken for air temperature and humidity, and surface temperature over the period of 1.5 years. Instantaneous measurements were taken over one summer and one winter period three times a day: before sunrise, in the afternoon and after sunset. MRT was calculated using Rayman 1.2 software, while the PET was measured through It was observed that the urban geometry can directly affect the outdoor thermal comfort of urban canyons and the energy required for cooling the buildings. Compact urban forms, with higher H/W ratios, are better suited to hot climates, since maximum shading can be achieved. There is a strong diurnal variation in the temperature in the shallow urban canyon as compared to the deep canyon; and hence it was concluded that a areas with higher H/W ratios are capable of reducing urban heat islands, as compared to areas with lower H/W. (18). In a similar study done in the city of Curitiba, Brazil, the impact of urban geometry and street orientation was done using the sky view factor (SVF). The study focuses on a pedestrian street in downtown Curitiba, 19 monitoring points were selected presenting different characteristics with regard to SVF or axis orientation. Fisheye imagery was used to determine the SVF. A pair of identical weather stations was used to simultaneously monitor 17 Final Report on Urban Planning Characteristics to Mitigate Climate Change in Context of Urban Heat Island Effect two different urban locations. Measurements were made for air temperature and humidity, wind speed and direction, solar radiation and globe temperature. Additionally, a comfort survey was carried out with the local population by means of a questionnaire. Relationship between Mean Radiant Temperature and SVF was established and it was suggested that the SVF is a limited parameter to describe the irregularities of urban geometry for the purpose of daytime outdoor comfort studies. Although it was verified that on hotter days, locations with a higher SVF can provide greater discomfort compared to those with lower SVF. (19). In a study done in the city of Chennai (20), a simple method has been presented to study the effect of physical features of an urban society over its microclimate and the outdoor thermal comfort. Six urban locations with different densities (H/W ratios) have been selected, at each location; three streets with different orientations (N-S, E-W, and NE-SW) are identified for monitoring. The measurements have been done during the hottest months of April, May and June. The ground cover type, as a percentage, is calculated for a region of 200m x 200m for each location. Daily measurements were made for five clear days at all street orientations, from 9:00 in the morning to 17:00 in the evening, over the interval of 30 minutes. Physiological equivalent temperature (PET) for the six locations was calculated and through regression analysis, it was observed that H/W ratios cannot alone govern the PET of a given location; the effect of green cover also requires consideration. Hence a new scale, called the HXG (Height/Width x Green Cover) scale was developed, which is the product of the H/W ratio and the percentage of green cover of a given area. This HXG scale provided a greater regression coefficient hence proving to be more accurate than H/W ratios alone. 3.11Urban Heat Island Studies in India Various UHI studies have been carried out in the developed and de