In the race to reach urban resilience, communities worldwide are quickly recognizing the critical role of addressing the Urban Heat Island (UHI) Effect within their disaster preparedness plans. But while it can be inferred that the UHI effect likely relates to rising temperatures and the growing impacts of climate change, it’s important to identify what makes the Urban Heat Island Effect such a significant threat.
What is the Urban Heat Island Effect?
The Urban Heat Island Effect is a phenomenon that affects urban areas, specifically those that experience significantly higher temperatures than their surrounding rural areas. The temperature disparity in these areas is most pronounced during the night when urban areas retain much of the heat absorbed during the day. The result? Warmer nighttime temperatures compared to rural counterparts and neighboring communities. The UHI effect is primarily driven by human activities and the environments we’ve built, which alter the natural thermal characteristics of urban areas.
Several notable factors contribute to the occurrence of the UHI effect. Most prominently, as communities replace the natural vegetation in an area with impervious surfaces (including asphalt, concrete, and building materials), these materials absorb and lock in heat during the day. Ultimately, this creates a thermal hot zone, elevating temperatures in these areas long after the sun has set. In dense cities, the concentration of buildings and infrastructure reduces the amount of open space and vegetation significantly, limiting shade and reducing cooling processes like evapotranspiration.
Additional factors continue to put even more strain on urban environments. Industrial processes, transportation, and energy consumption all release heat, further exacerbating the UHI effect. Waste heat from vehicles, air conditioners, and other sources adds further stress to the overall heat load in these urban areas, contributing to a more pronounced difference in temperatures between cities and their rural neighbors. As cities continue to grow and urbanize, the UHI effect poses significant challenges for public health, energy consumption, and overall livability.
While many might think of natural disasters as sudden or significant one-time impacts, Prometheus acknowledges the potential for disaster that is baked into phenomena like the Urban Heat Island Effect. If left unchecked, these rising temperatures will result in continued displacement of citizens, damage to infrastructure, and an overall compromise in safety, health, and comfort for communities across the globe. By definition, the UHI effect is a significant but underacknowledged natural disaster that demands our attention – and our action.
Cooling Things Down: Cities That Set a Standard
1. Tokyo, Japan
As one of the world’s most populous cities, Tokyo’s 14 million residents face significant challenges related to urban heat. As temperatures soar in the summer months, the city experiences intense heatwaves that pose serious risks to residents. “Human-caused global warming has contributed to a 1.5°C (2.7°F) increase in temperatures in Tokyo since 1964 and a 2.86°C (5.14°F) increase since 1900. That is nearly three times the global average.” (Source: NASA’s Earth Observatory) In response to these rising temperatures, Tokyo has integrated UHI mitigation measures into its disaster preparedness plans.
“In April [2023], Tokyo released its Biodiversity Strategy for 2030, which notes the heat island mitigation effects of green spaces, roofs and walls. Although the metropolis has not set specific greening goals, it plans to promote various “nature-based solutions,” including further green infrastructure, going forward.” – The Japan Times
One key initiative is the promotion of green spaces and cool roofs. Investments in park expansions, the creation of green corridors, and incentives for the installation of cool roofs on buildings have enabled Japan to make progress toward UHI effect mitigation while enhancing the city’s overall resilience to heat.
We’ve mentioned Japan’s early warning systems several times throughout The Prometheus Resource Center, and with good reason. Tokyo’s early warning systems and heat emergency response plans have been implemented to protect vulnerable populations during extreme heat events. Cooling centers, the distribution of heat safety information, and hands-on assistance for those in need are just some of the measures Tokyo prioritizes throughout its preparedness plans.
2. Los Angeles, USA
Known for its sprawling urban landscape and Mediterranean climate, Los Angeles faces similar challenges related to urban heat. Thankfully, the city has been at the forefront of implementing innovative strategies to combat the UHI effect, enhancing overall disaster preparedness across the city.
According to LA County’s Public Health website, a 5-point plan has been initiated to keep Los Angeles on track and reduce the health impacts of climate change across the area. This plan centers around these concepts: inform, promote, provide, build, and adopt. Additionally, LA recognizes the use of green roofs, green spaces, and cool pavements as a priority across infrastructure improvements.
LA’s Cool Roof program incentivizes property owners to install reflective roofing materials that can help reduce heat absorption and lower indoor temperatures. Additionally, Los Angeles has prioritized the expansion of urban green spaces to provide cooling relief and improve air quality. By integrating these UHI mitigation measures into emergency response plans, and establishing outreach programs to educate residents, Los Angeles continues to mitigate the impacts of extreme heat.
3. Melbourne, Australia
Often regarded as one of the world’s most livable cities, Melbourne has been proactive in addressing the UHI effect, incorporating heat resilience into disaster preparedness plans. As rising temperatures increase the frequency of heatwaves across Melbourne, the city has implemented several measures to protect residents from severe heat.
In addition to a significant emissions reduction plan, Melbourne has also invested in an Urban Forest Strategy, aiming to increase tree canopy cover and provide cooling relief in urban areas. In hopes of increasing tree canopy cover from 22% to 40% by 2040 (Source: City of Melbourne), Melbourne has made several resources available to organizations and community members willing to help.
Melbourne has also developed heatwave response plans and public awareness campaigns, educating residents about the importance of staying cool and hydrated during extreme heat events. These measures can help reduce the impacts of heat waves, improving community resilience over time.
Embracing Sustainable Solutions for a Cooler Urban Future
As climate change continues to exacerbate the Urban Heat Island Effect, it’s more important than ever to prioritize UHI mitigation measures within disaster preparedness plans. This essential effort can help communities strengthen their resilience. By looking at the examples set by cities like Tokyo, Los Angeles, and Melbourne, communities across the globe can do their part to champion innovation in the face of the UHI effect.
