8  Urban Heat Island

In this week, we will present some environmental issue related to temperature, which is the Urban Heat Island, and may need an involvement of remote sensing for the solutions.

8.1 Summary

8.1.1 What is it?


Source: World Meteorological Organization (WMO)

The Urban Heat Island (UHI) effect refers to the phenomenon where urban areas experience higher temperatures than their surrounding rural areas. This occurs mainly due to the replacement of natural vegetation with built surfaces, such as buildings, roads, and other infrastructure, which absorb and retain more heat. The UHI effect can exacerbate energy consumption, air pollution, and greenhouse gas emissions, as well as negatively impact human health and comfort.

  • The causes of Urban Heat Island

    There are two main causes of UHI which are following:
    1. Heat-absorbing materials: Buildings, roads, and other infrastructure in urban areas absorb and re-radiate heat, contributing to increased temperatures. In other words, there are more dark surfaces that retain heat
    2. Less vegetation: Urban areas have less vegetation, which reduces the amount of shade and cooling through evapotranspiration, leading to increased temperatures.
    the other causes of this issue are following:
    1. Urban geometry: The arrangement and density of buildings in urban areas can affect air circulation and solar radiation absorption. Tightly packed buildings, narrow streets, and tall structures can trap heat and limit the movement of cool air, exacerbating the UHI effect.
    2. Heat Generated from Human Activities: Various human activities in urban areas, such as transportation, industrial processes, and air conditioning systems, generate waste heat, which contributes to increased temperatures in cities.
    3. Reduced wind flow: Urban structures can obstruct and slow down wind flow, which would otherwise help disperse heat and bring in cooler air from surrounding areas. This reduced wind flow contributes to the buildup of heat in urban environments.

To know more about Urban Heat Island, check this video made by CASA students:
Urban Heat Island Interpretive Dance

8.1.2 Urban Heat Island Situations Around the World

  • In developed countries: Extensive research has been conducted on the UHI effect in major cities such as New York, London, Tokyo, and Sydney. These cities often have large impervious surfaces, high building density, and limited green spaces, contributing to the UHI effect. Governments and city planners in these regions have been implementing various mitigation strategies, including increasing urban greenery, promoting energy-efficient buildings, and optimizing urban design.

  • In developing countries: the UHI effect is often more pronounced due to rapid urbanization, uncontrolled land use changes, and limited resources for sustainable urban planning. Cities such as Delhi, Beijing, São Paulo, and Lagos experience severe UHI effects, compounded by the lack of green spaces, poor air quality, and inadequate infrastructure. In these cities, addressing the UHI effect is crucial for improving public health, energy efficiency, and overall quality of life.

8.2 Applications

Next, we will see how can we tackle with this critical issue.

8.2.1 Policy and Implementation

Global Policy

  • The Sustainable Development Goals (SDGs) provided by UN also recognised the critical situation of this issue and call to action to ameliorate this issue.
  • Goal 11: “Make cities and human settlements inclusive, safe, resilient and sustainable”
  • SDG 11 issue brief: “Investing in parks and green spaces in urban areas will help to ameliorate the urban heat island effect and improve air quality in urban spaces.”
  • It can be seen that UN also recognised this global challenge and underlined this issue in the issue brief document. However, there is still no targets to address this issue directly.

Local Policy

There are many cities choose to issue the policy and strategy to amend the situation. Here are some examples:

City Strategy Action Outcomes
Barcelona, Spain Superblocks model Reorganizes the city’s streets to prioritize pedestrians and non-motorized transportation, creating large car-free zones Reducing traffic, better air quality, free up space previously occupied by cars for allowing for the creation of new parks and also reduce noise in the city
Melbourne, Australia Urban Forest Strategy, Green Our City Strategic Action Plan Plant more trees, improving urban landscapes, and creating green spaces Increased green spaces, tree planting, and green roofs, which have led to improved microclimate, better air quality, and enhanced biodiversity in the city.
Medellín, Colombia Green Corridors Project Create green corridors throughout the city by planting trees and vegetation along streets, sidewalks, and waterways More green corridors along streets, riverbanks, and other urban spaces, better air quality, improved microclimate conditions and even reduce temperature 2 degrees of surface temperature.
Perth, Australia Urban Forest Plan, Greening Plan 2020-2050 Plant more trees in public spaces and encouraging private property owners to plant trees on their land Increasing tree canopy cover and green spaces, better air quality, and enhanced urban biodiversity
Tokyo, Japan Heat Island Mitigation Act and Tokyo Metropolitan Environmental Security Ordinance Promote the use of cool pavements and roofs Implemented cool pavements, green roofs, and increased green spaces, which have contributed to reduced urban heat island intensity and improved living conditions for the city’s residents.

It could be seen that there are a lot of benefits resulting from environmental policies related to temperature. Therefore, we should consider more about the effects in environments of everything we plan to do in the future.

8.3 Reflection

  • Content: the Urban heat Island effect is quite new to me. Honestly, I have never heard about this issue before, although I am from Thailand, the country with very high temperature. Next step for me is to find out more about this issue in Thailand and what are the implementation plans to tackle with this issue in my country. I researched on this issue a liitle bit and still have not found any documents or policies related to this issue from the government. This lecture enlightened me to realise the other critical issue that should be considered.

  • Applications: It is very amazing to see how each city tackle with the Urban Heat Island issue with the different way. The outcomes from each strategy are very promising. I was inspired by the video of Superblocks model shown in the lecture that we can really design our city and there is the room to solve every challenging issues even though how big it is. Moreover, I have just realised that cooler only 2 degrees of temperature can really better our society.