Multiple city hubs, dispersed parks keep metro areas cooler

Compared to "monocentric" development, "polycentric" spatial patterns better distributethe density of urban cores and curb the sprawl of impervious, heat-absorbing surfaces, according to the analysis of 50 city regions in Germany. Particularly in larger urban areas, polycentric development can moderatethe urban heat island effect, when built-up areas can be several degrees hotter than surrounding rural areas -- a potentially dangerous phenomenon during heat waves that are expected to grow more common due to climate change.

While urban tree canopies and green spaces are known to provide cooling benefits, the researchers also found that smaller, decentralized open spaces across a metropolitan area are more effective at reducing urban heat compared with a larger, more centralized green space pattern.

The findings suggest cooling strategies that merely address the role of urban density may be insufficient, and point to the need for regional-level planning to coordinate land-use patterns across metropolitan areas.

Stephan Schmidt, associate professor of city and regional planning, and Wenzheng Li, a doctoral student in the field of city and regional planning are co-authors of "Can Spatial Patterns Mitigate the Urban Heat Island Effect? Evidence from German Metropolitan Regions," published in the journal Environment and Planning B: Urban Analytics and City Science.

Schmidt and Li said the findings have implications for regional-level planning that are already institutionalized in German and European systems that promote polycentric development as a goal. But they said the study can also inform planners and policymakers more broadly to coordinate regional green spaces patterns and to increase the density of suburban nodes.

"There are many other benefits to doing that -- limiting sprawl, concentrating population and economic activity, promoting public transit use and increasing affordable housing," Schmidt said. "And in addition, you'll have this positive impact on the metropolitan-scale heat island effect."

The research was supported by the Cornell Sage Fellowship for doctoral students.