Not everyone is aware of this, but when it’s summer and people are trying to escape from the heat, the common places that everyone will mention are beaches, forests, parks—but rarely will someone mention the city. Why? Because when summer hits, everyone knows that the city or urban environment will be exponentially hotter. Even when when you check on your phone the temperature of a local city and compare it to the temperature of a rural area next door to it, it’s quite consistent that the city will be warmer by a few degrees more. But if I were to ask any of you what makes a city warmer than its rural counterpart, most of you would dance around the answers and be unsure why this phenomenon exists. And don’t worry, you’re not alone, as I used to wonder the same thing.
Luckily, there’s a term for this! It’s called urban heat island effect.
What drives your city to develop urban heat island? In the city of Los Angeles, California, we have one of the worse urban heat island effects since we are mostly sunny throughout the year with few days of rain.
- Our high density of buildings, road pavements, and roofs absorb solar radiation throughout the day and then the infrastructure will release the energy during the night, which is why urban residents don’t get a cooling relief at night.
- On top of the released energy at night, the skyscrapers in Los Angeles serve as an obstacle that blocks the cooling wind currents from cooling the city, interfering with the natural patterns of convective circulation, a process that allows less dense, warm air to rise and cooler air to descend.
- Additionally, the impervious surfaces from conventional pavements in Los Angeles heat up the rainwater that we get few times throughout the year and push it into sewers instead of allowing it to evaporate to cool the air that urban residents desperately need.
What are the impacts of urban heat island effects? The urban heat island effect in Los Angeles disproportionately impacts the community. Communities of low-income and vulnerable health groups across the county of Los Angeles are directly and negatively impacted by the urban heat island effect.
- The current dark conventional pavements and dark roofs that increase albedo absorb the solar radiation and heat up homes and buildings, and people of color and low-income communities suffer because they have preexisting conditions and are likely unable to afford air conditioning. With the two factors combined, we had an increase in emergency room visits that occurred in California due to the extreme heat exacerbating the symptoms of chronic illnesses.
- Even if we had everyone owning air conditioning, the effects of urban heat island wouldn’t go away; rather, it would worsen due to the increased energy consumption and additional greenhouse gas emissions associated with it. While wealthy businesses in Los Angeles are able to afford the additional energy consumption, they are producing more greenhouse gas emissions, intensifying the cycle of urban heat island, which forces low-income communities, older adults, and younger children to continue to bear the consequences of urban heat island effects.
- With the urban heat island effect interrupting the normal routine of convective circulation, we are finding that there is a temperature inversion that traps air pollutants within the city. As a result, Los Angeles has ozone air pollution that increase the risk and vulnerability of communities with respiratory and cardiovascular health issues.
How can we adapt to the effects of urban heat island?
- We can provide cooling centers in neighborhoods that have low-income individuals, seniors, young children, and the homeless population. We need to reach out to Latinos because they make up 50% of the population in Los Angeles; yet they embody 67% of the high-risk community when it comes to thermal stress.
- We can hold town hall meetings to encourage the public to check up on their high-risk family members and neighbors to ensure that they have properly functional water and energy systems so that they can cool themselves down with cold drinking water and air conditioning.
- We can call public health officials to ask them to create a system that announces heat warnings and gives reminders to the public on what to do during heat waves: conserve energy, stay indoors, and what symptoms of heat-related illnesses to look out for.
How can we mitigate the effects of urban heat island?
- We can replace our dark rooftops with white rooftops, so that we can reduce the albedo, which is the light radiation that is reflected from a surface. When we shift to white roofs, we are reducing the heat absorption of surfaces, resulting in decreased urban temperatures and offsetting a portion of warming that comes from the greenhouse gases.
- We can plant more trees and plants to provide more shade and cooling relief for the urban environment and its residents. This can be incorporated in our backyard, neighborhood, or requested into the urban planning of Los Angeles in the forms of planting more trees around buildings, on streets, and in parking lots where there are plenty of roads and pavements that absorb solar radiation and transmit it as heat. If more vegetation provided shade to these infrastructure, it would absorb less solar radiation and transmit less heat; thus, reducing the development of urban heat island. Additionally, more vegetation means more opportunities for evapotranspiration to occur throughout the city, providing cooling relief.
- We can reach out to and demand urban planners of Los Angeles to make the swap from conventional pavements to cool pavements. Since Los Angeles is mostly sunny throughout the year, cool pavements will dramatically reduce the heat absorption from solar radiation because they will reflect more of the solar energy compared to conventional pavements. Currently, the city has covered Los Angeles streets with 150 lane-miles of cool pavement, but we can continue to do more.
I hope you have learned something about urban heat island effect and why it makes cities notoriously warmer than any other area that you’ve been to. While none of us may want to live in Los Angeles, some of us may want to visit it to see a family member, catch up with an old friend, or pursue your dream in acting. I understand that it’s always hot and unpleasant in Los Angeles, but now that we understand why it is the way it is, we can suggest and enforce new changes so that Los Angeles can be more pleasant for our family and friends. And perhaps, one day, it might not seem like a bad idea to live and work there as an urban planner, or anything you want to be.
References:
- Environment: The Science Behind the Stories by Jay Withgott & Matthew Laposata
- https://www.theguardian.com/us-news/2023/jan/03/los-angeles-is-becoming-too-hot-to-bear-can-it-design-its-way-cooler
- https://calepa.ca.gov/climate/urban-heat-island-index-for-california/understanding-the-urban-heat-island-index/
- https://www.epa.gov/heatislands/using-trees-and-vegetation-reduce-heat-islands
- https://www.epa.gov/heatislands/heat-island-cooling-strategies
- https://www.epa.gov/heatislands/adapting-heat#:~:text=City%20officials%20can%20also%20incorporate,extremes%20during%20future%20heat%20waves.