Climate change and increasing urbanization are linked. Over half of the world’s population lives in cities, where they account for a lot of energy use and carbon emissions. Cities concentrate people, business, industry, and infrastructure in a small area. This leaves them more exposed to the effects of climate change, something urban planners need to consider for the decades ahead. Three colors could help.
Dark asphalt and rooftops absorb heat during the day and continue to radiate it at night. The built environment is warmer – by up to 3 degrees Celsius – than rural areas, in part because the lack of space between buildings prevents heat from escaping. Lighter colors, by contrast, reflect about four-fifths of sunlight back into space. Researchers estimated in 2010 that painting the roofs of the world’s major cities white would reduce average temperatures by 0.4 degrees Celsius. This would lessen the need for air conditioning and thus conserve energy. Some cities are testing the idea. New York’s CoolRoofs initiative has painted more than 500,000 square meters of the city’s rooftops white, while Los Angeles has done so with some of its streets.
Vegetation reflects sunlight, provides shade, filters air pollutants, and produces oxygen. Debate.Energy has already reported on innovative horizontal trees growing from the façades of buildings. Although the urban space for greenery is limited, options are available. Some experts recommend making new buildings taller rather than encroaching on green spaces with new construction. And rooftops could be greener. Although a shopping center roof in Berlin’s Wilmersdorf district is home to two weed-eating sheep and four bee hives, gardens and green spaces adorn at most 2% to 8% of Germany’s roofs. The potential is enormous.
Heavy rain can quickly overwhelm some cities’ sewer systems, like it did in August 2019 in Berlin. It would actually be much better if rainwater evaporated slowly on grassy areas or permeable soil, which would allow it to cool the air at the same time. That’s why urban planners are turning to multifunctional retention areas. For example, a lower-lying park with greenery could be designed so that longer periods of rain temporarily transform it into a small lake. Retaining rainwater in this way would relieve the sewer system. Urban farming and indoor farming could do the same if they irrigate with rainwater or sullage (also known as graywater). Urban artificial wetlands, which conserve both water and green space, are another option.
Paint the town…
There’s no panacea. More urban greenery, for example, would require more water. That could become a problem if global warming reduces rainfall (desiccated vegetation actually absorbs more heat than concrete). Fabian Dosch of Germany’s Federal Institute for Research on Building, Urban Affairs and Spatial Development in Bonn points out that what works in one city might not be transferable to another. In short, each city will have to find its own palette of climate-friendly colors.