A new study shows that rivers help cool cities when they need it most, during the hottest hours of the warmest months.
Since losing their prominence as shipping corridors, the rivers runing through cities have not been a boon. They smell. They serve as sewage dumps. They overflow. They catch on fire. But rivers are staging a comeback. Cities are working to clean them up and build riverfront developments. At least one city is even planning on uncovering rivers that have been paved over.
Besides the recreational possibilities, urban rivers could provide another benefit to cities: cooling. But while city dwellers flock to the riverbank on a hot summer day, there’s been little research on how rivers' cooling effect works and what could be done to maximize its impact. But a new, multi-year study from the University of Sheffield in England shows that rivers help cool cities when they need it most, during the hottest hours of the warmer months.
The study is part of a larger project looking at urban river corridors and sustainability and a broader trend of considering how water and water management can help create low-energy cities. Because cities are full of hard surfaces that absorb heat and slough off water into drainage systems, they retain heat and are significantly warmer than the rural areas that surround them. More heat means more energy is needed to cool them down.
Water, of course, is very effective at cooling, and buildings and streets can be designed to take advantage of that feature. Parks are cooler than their surroundings in part because their ground absorbs more water. Collected rainwater can not only provide irrigation, it can cool buildings as it evaporates from rooftop storage ponds.
The study from the University of Sheffield shows that the cooling effects of rivers can spread well beyond their banks, particularly if the surrounding urban areas are well-designed. One type of development modeled in the study contained more open, green spaces, which allowed the cool temperatures of the river to bring down the temperature of the entire area. The river could have the biggest impact at the peak of afternoon heat, which could bring down air conditioning costs significantly.
Accepting that nature has a place in the city can help make cities thriving, dense communities. Turning vacant lots into green space can improve the health of the people who live around it and reduce violent crime in the neighborhood. Urban planners have always thought of rivers as resources. Now, instead of corridors for moving goods, they may become corridors for transporting light and air—the type of resources that too many cities have in short supply.