The urban heat island (UHI) effect, especially when considered together with climate change, represents a serious and growing threat to the competitiveness, livability, and inclusiveness of East Asia¡¯s cities. However, because it is a local effect, the leaders of these cities can significantly mitigate its impact on local temperatures while also further promoting greater adaptation to extreme urban temperatures. This ÐÓ°ÉÂÛ̳ report addresses three critical questions:
How strong is the UHI effect in East Asia, and how is it interacting with climate change?
Why should policy makers worry about the UHI effect and extreme urban temperatures more generally?
What can city leaders do to combat extreme urban heat?
How strong is the urban heat island effect?
On average, East Asian cities are 1.6¨C2.0 degrees Celsius (¡ãC) warmer than their immediate rural surroundings. Based on analysis of satellite data for 100 East Asian cities, land surface temperatures from 2016 to 2020 were, on average, 1.6¡ãC warmer in these cities than in rural areas within 2 kilometers and 2.0¡ãC warmer than in rural areas within 10 kilometers. Cities in Indonesia, Malaysia, and the Philippines¡ªwhere average temperatures can be up to 5.9¡ãC warmer¡ªsuffer from the strongest UHI effects.
UHI effects are much stronger than these averages in some neighborhoods and are strongest at night. The averages mask considerable variation in the strength of the UHI effect within cities. For example, new research for this report shows that in Bandung, Indonesia, there are heat disparities of up to 7.0¡ãC between the hottest and coolest neighborhoods. Such thermal disparities between neighborhoods are typical of many cities, both in East Asia and globally. The UHI effect is typically stronger at night than during the day because the heat stored in the built environment is gradually released after sunset.
The UHI effect is often stronger in poorer neighborhoods. Within cities, a neighborhood¡¯s UHI effect is often, but not always, strongly positively correlated with its poverty rate. Stronger UHI effects in poorer neighborhoods result from a relative lack of urban greenery and a greater prevalence of impervious surface areas.
The UHI effect is a particular concern for tropical East Asian cities where humidity adds to the risk of overheating. These cities already have hot and humid baseline climates that are, furthermore, becoming even hotter and more humid over time because of climate change. For example, in Phnom Penh, Cambodia, the UHI effect already contributes to 23¨C25 heat wave days a year in the city¡¯s central districts. Fast forward to 2050, and the number of heat wave days a year is projected to more than double for those ne