Public Safety-Resilience and Regeneration of Communities

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Extreme heat

Extreme heat and heatwaves are becoming a significant concern for many world cities and communities, and it's rapidly worsening due to the impact of climate change. Extreme heat events have severe impacts on ecosystems, infrastructure, human health, and economies. These heatwaves are not only a consequence of escalating global temperatures, but they also symbolize an acute emergency for urban environments worldwide In several locations the extreme heat is exacerbated by poor air quality caused by smoke from wildfires.

Urban areas, characterized by their dense populations and significant infrastructural development, have become epicenters for extreme heat impacts. This phenomenon is exacerbated by the Urban Heat Island (UHI) effect, wherein the lack of vegetation and high prevalence of heat-absorbing materials lead to significantly warmer conditions in cities compared to their rural surroundings. The interplay of climate change, urbanization, and socio-economic factors means that heat risks in cities are escalating at an alarming rate.

The consequences of increasing urban heat are manifold and far-reaching. heatwaves pose considerable threats to urban infrastructure, disrupting essential services, exacerbating energy demands, and straining resources. Simultaneously, health concerns range from heat stress and heat-related illnesses to exacerbated chronic conditions and increased mortality rates. The ripple effects of extreme heat events can thus perpetuate socio-economic disparities, destabilize local economies, and compromise overall urban sustainability.

In the next sections, we will show how to identify the severity of extreme heat events and identify and implement actionable adaptive and mitigative strategies to reduce risk [1] and increase resilience [2]. We will present case studies from cities across the globe, demonstrating the universal nature of this crisis and the range of strategies combining infrastructural changes, policy interventions, technological advancements, and community engagement currently being deployed.

Monitoring and Benchmarking Extreme Heat- KPIs

Temperature- Metric: (°C/°F) is the most obvious indicator of the warming planet. NOAA National Centers for Environmental Information provides detailed information on both local and global temperature variation. Since the dawn of the industrial age the global average temperature had risen by approximately 1.1 degrees Celsius (about 2 degrees Fahrenheit) above pre-industrial levels. The consequences of this warming include more frequent and intense heatwaves and changes in weather patterns. Mean or peak daytime temperature Metric: Mean or peak daytime local temperature by direct measurement, PET calculation or modelling (°C), or by PMV-PPD calculation (unitless value) Green urban infrastructure can significantly affect climate change adaptation by reducing air and surface temperatures with the help of shading and through increased evapotranspiration. Conversely, green urban infrastructure can also provide insulation from cold and/or shelter from wind, thereby reducing heating requirements. By moderating the urban microclimate, green infrastructure can support a reduction in energy use and improved thermal comfort.

Heatwave Risk Metric: number of combined hot nights (>20°C) and hot days (>35°C) Heatwave is a period of prolonged abnormally high surface temperatures relative to those normally expected. Heatwaves can be characterized by low humidity, which may exacerbate drought, or high humidity, which may exacerbate the health effects of heat-related stress such as heat exhaustion, dehydration and heatstroke. Heatwaves in Europe are associated with significant morbidity and mortality. Furthermore, climate change is expected to increase average summer temperatures and the frequency and intensity of hot days.

Urban Heat Island (UHI) effect Metric: (°C/°F) This indicator focuses on the urban heat island (UHI) effect, wherein a significant difference is observed in air temperature between the city and its surroundings. The UHI effect is caused by the absorption of sunlight by (stony) materials, reduced evaporation and the emission of heat caused by human activities. The UHI effect is greatest after sunset and reported to reach up to 9°C in some cities, e.g., Rotterdam.


Reducing extreme heat and heatwaves in urban areas is an urgent task for many cities and communities given the increasing intensity of heatwaves as a result of climate change. Below are some strategies cities can consider:

  • Urban Greening: Increasing the number of trees, plants, and green spaces in a city can help to reduce temperatures. This is because vegetation reduces heat through a process known as "evapotranspiration” and provides shade that cools the surrounding areas. Additionally, green roofs and walls can be used to cool buildings and further reduce temperatures. Urban forests also contribute to carbon sequestration, thus mitigating climate change.
  • Urban Planning and Design: Implement strategies to reduce the heat island effect. This includes constructing buildings with cool or green roofs, using lighter-coloured materials in pavements and other urban infrastructure to reflect more sunlight, and ensuring that buildings are adequately spaced to allow for airflow.
  • Water Features: The introduction of water features such as ponds, fountains, and artificial lakes can help to reduce urban heat through evaporative cooling.
  • Improved Building Design: Increasing the energy efficiency of buildings can reduce the need for air conditioning, which is a significant contributor to urban heat. Passive cooling strategies such as natural ventilation, shading, and insulation can be very effective in this regard.
  • Community Education and Behavior Change: Educating residents about the impacts of heatwaves and how to stay cool can help to mitigate the health impacts of extreme heat. Encouraging behavioral changes such as reducing energy use during peak times can also help to reduce heat production.
  • Infrastructure Adaptation: Adopting heat-resilient infrastructure such as thermally comfortable public transportation, cooling centers, and shaded public spaces can protect vulnerable populations during heatwaves.
  • Early Warning Systems and Heat-Health Action Plans: Implementing robust heat-health warning systems can alert the public when heatwaves are expected, allowing them to take precautions. These systems need to be linked to heat-health action plans that detail how to respond to these warnings.
  • Climate-sensitive Urban Development: New development projects must take into consideration future climate conditions including rising temperatures and frequent heatwaves.
  • Engagement with stakeholders: Partnering with local communities, businesses, non-profits, and other stakeholders to implement these measures can ensure they are successful and tailored to local needs.
  • Policy Interventions: City governments can implement a range of policy interventions to promote these strategies, such as requiring green roofs on new buildings, offering incentives for energy-efficient design, or creating zoning laws that promote the creation of green spaces.

It is important to take a holistic approach to reducing urban heat, as these strategies can often have additional benefits such as improving air quality, enhancing biodiversity, and improving residents' well-being.

Alarm systems and sensors technologies for warning about extreme heat

Extreme heat warning systems typically involve a combination of meteorological equipment and data analysis to predict high-temperature events. They are typically larger-scale systems employed by meteorological institutions. Here are the primary types of systems:

  1. Weather Stations: They play a crucial role in detecting environmental changes, including temperature. They are equipped with various sensors to measure temperature, humidity, pressure, wind speed, and more.
  2. Remote Sensing Systems: Satellites equipped with thermal sensors can monitor the Earth's surface temperature and other climatic parameters. These systems can provide comprehensive, global coverage, enabling scientists to identify potential heatwaves.
  3. Heat Health Warning Systems (HHWS): These systems use weather forecast data to predict upcoming periods of extreme heat that could have impacts on human health. HHWS can issue warnings several days in advance of a heat event, allowing authorities to take action to protect vulnerable populations.
  4. Automated Weather Sensors: These are designed to capture weather data at frequent intervals and transmit the data to a central system for analysis. This can include temperature data that is used to forecast heatwaves.
  5. Internet of Things (IoT) Devices: These devices can help monitor and control the indoor environment. For instance, smart thermostats can detect high temperatures and adjust accordingly to ensure a comfortable indoor climate.
  6. Weather Apps and Notifications: Many smartphone applications use meteorological data to provide users with timely alerts about extreme weather conditions, including extreme heat.
  7. Environmental Monitoring Systems: These systems monitor various environmental factors, including temperature, in sensitive areas like data centers, manufacturing plants, and warehouses. When the temperature exceeds a set threshold, the system can trigger an alarm or notification.

Extreme heat warning systems are often part of a larger environmental monitoring effort that includes monitoring other meteorological phenomena, and extreme heat warnings often rely on accurate weather forecasting models as well. Response to these warnings often involves community-based heatwave action plans, especially in areas that are prone to high temperatures.

Case Studies:

Several cities worldwide have successfully used tools and implemented strategies to reduce the impacts of extreme heat and heat waves. Here are some examples:

San Francisco Heat and Air Quality Resilience Plan (HAQP). It establishes a framework to address current local extreme heat and wildfire smoke events while preparing for future ones. It is the first comprehensive approach to identify and address the public health and infrastructure impacts of extreme heat and wildfire smoke. Foundational to the approach is an understanding that these health impacts are inequitably distributed.

'Healthy Design City' is a digital tool that draws on robust open-source datasets to provide nationally-consistent indicators of tree cover and health and equitability at a neighbourhood level of the urban built environments across on in Canadian cities

Melbourne, Australia: Melbourne has an Urban Forest Strategy aiming to double the tree canopy cover to 40% by 2040. The city also has a Cooling Melbourne Strategy to help tackle increasing heatwaves, focusing on creating green and cool roofs, walls, and facades, increasing urban forests, and using water-sensitive urban design for cooling.

Stuttgart, Germany: Stuttgart has developed a sophisticated system of "climate maps" and "climate function maps" to inform urban planning. This includes creating wind corridors to improve airflow and reduce heat build-up, and preserving and creating green spaces for cooling.

Tokyo, Japan: Tokyo introduced the "Tokyo Green Building Program"requiring all large new buildings to install green roofs, solar panels, or other heat-reducing features. The city is also expanding its urban green spaces and street trees.

New York City, USA: The NYC CoolRoofsinitiative encourages building owners to coat their rooftops with a white, reflective surface to reduce building temperatures. The city's OneNYC 2050 strategy aims to have a park within walking distance of every resident, further contributing to urban cooling. New York also has an extensive network of cooling centers for use during extreme heat events. Sign in to NYC Mayor's Office of Resiliency

Paris, France: After the deadly 2003 heatwave, Paris developed an ambitious adaptation strategy which includes creating green roofs and walls, planting trees, and redesigning public spaces to include more vegetation and shade. It also has a comprehensive Heatwave Plan that includes warning systems and cooling centers.

Ahmedabad, India: In response to a heatwave that claimed over a thousand lives in 2010, Ahmedabad developed a Heat Action Plan, which is now a model for other Indian cities. The plan includes an early warning system, public awareness campaigns, and a coordinated inter-agency response plan.

Chicago, USA: Chicago has one of the most extensive roof program in the U.S., including a green roof on City Hall. The city's climate action plan also emphasizes the importance of increasing tree canopy and green spaces.

These examples show how cities of different sizes and climates can implement strategies to reduce the impacts of extreme heatwaves. Each city has unique circumstances and capacities, so strategies should be tailored to local conditions and needs.

  1. "National Risk Index" 2023-07-27
  2. "The Resiliency Compass: Navigating Global Value Chain Disruption in an Age of Uncertainty" 2020-07-01 2021-07-01. PDF file icon.svg