How planning for extreme temperatures builds better, safer cities

Avoiding head-on collisions, dodging dog poop on the sidewalk, trying not to spill hot coffee — these are just a few of the obstacles commuters come up against daily as they struggle to get to work in the city.

But urbanites face a bigger challenge, one that has the potential to be way more dangerous than stepping in something nasty. Extreme hot and cold temperatures drive weather-related deaths in cities. And the problem — especially deaths caused by extreme heat — is worse than researchers thought, a study published this week in the journal Science Advances suggests.

Data from 16 major American cities reveals how urban populations tend to move throughout the day — and how that changes their potential for exposure to extreme temperatures.

In the case of heat waves, people in cities experienced temperatures 1.9 degrees Celsius higher than predicted by weather forecasts. The largest increases were seen in Seattle and Los Angeles, the researchers found.

When it comes to extreme cold, however, commuting actually tempered the effects of exposure by 0.6 degrees Celsius, on average. That effect was especially apparent in Chicago, where population movement is magnified during times of extreme low temperatures.

Modified exposure to temperatures is part and parcel of daily commutes, the researchers suggest. As a result, traveling through a metropolitan area might experience different temperatures as they make their daily rounds — some of which could be extreme.

If greenhouse gas emissions continue at current rates — if it’s “business as usual” essentially — that effect is only going to worsen as the climate continues to change.

Better city living needs better city planning

More than half of the world’s population lives in cities, and the number is expected to grow to two-thirds by 2050.

The risk heat waves pose to health is a serious concern, and city planners and engineers need to create systems to deal with extreme temperatures, the researchers write. The findings could also help to make weather reports more accurate and create alert systems for residents, enabling them to plan ahead for extreme temperatures.

Insulating cities against these extreme weather effects means working to mitigate the urban heat island effect, the researchers say. Strategies may involve things like building with lighter materials and planting more vegetation in cities. Past research has shown that reserving some urban space for greenery can also have big health benefits and even add years to people’s lives.

This work suggests that paying more attention to heavily-trafficked commuter routes could also help city planners better prepare for what’s to come with a changing climate, the researchers say.

>Abstract:

Exposure to extreme temperatures is one primary cause of weather-related human mortality and morbidity. Global climate change raises the concern of public health under future extreme events, yet spatiotemporal population dynamics have been long overlooked in health risk assessments. Here, we show that the diurnal intra-urban movement alters residents’ exposure to extreme temperatures during cold and heat waves. To do so, we incorporate weather simulations with commute-adjusted population profiles over 16 major U.S. metropolitan areas. Urban residents’ exposure to heat waves is intensified by 1.9° ± 0.7°C (mean ± SD among cities), and their exposure to cold waves is attenuated by 0.6° ± 0.8°C. The higher than expected exposure to heat waves significantly correlates with the spatial temperature variability and requires serious attention. The essential role of population dynamics should be emphasized in temperature-related climate adaptation strategies for effective and successful interventions.