A new study helps show how builders and city planners can minimize the materials needed to accommodate the planet's future population.
"How we plan cities today will shape their material demand for decades," said Jinchao Song , the first author of the new study and a U-M research fellow with the School for Environment and Sustainability, or SEAS . "Using materials more efficiently can help cities accommodate future population growth while reducing the emissions associated with construction. If we use less material, we will have less energy consumption and carbon emissions."
In the study, published in the journal Nature Cities, Song and colleagues combined high-resolution satellite imagery and other geospatial data with building material information to calculate the weight of 606 million buildings around the world. Working with experts from China, Denmark and the Netherlands, she then analyzed how economic conditions, population density and characteristics of the built environment, including urban form, were associated with material-use efficiency across cities.
Urban form considers how densely buildings are packed, how tall they are and how much variation there is in building height throughout the city. The researchers found that cities with a dense coverage of uniformly short buildings maximized floor space per person while minimizing the materials used.
"The weight of buildings provides a complementary, physical angle for us to understand the processes and implications of urbanization," said Gang Liu , corresponding author of the study and chair professor at the College of Urban and Environmental Sciences at Peking University.
Although previous studies have examined material usage and weight, most focused on larger national or regional scales, Song said. The relatively few studies that did examine these factors at a finer, building scale tended to focus on high-income countries, leaving the Global South underrepresented. And it's in these lower-income countries where experts expect the most future population growth and urbanization, potentially driving substantial demand for new building materials.
"We've created this globally consistent database at the level of individual buildings, allowing us to identify patterns that coarser estimates could not capture," Song said.
This enabled a number of findings beyond the most material-efficient urban form. For example:
The total mass of the 606 million buildings was 835 billion metric tons, or gigatonnes, just shy of the weight of all the world's plants (which is around 900 gigatonnes ). China possesses roughly a quarter of that total building weight.
High-income countries, which are home to about 16% of the world's population and account for 46% of global building material consumption, have the most cities in the optimal urban form. More than 40% of the dense and uniformly low cities are in high-income countries.
Low-income countries have more than 80% of the sparse, uniformly low cities, compared with 5% for high-income countries.
While China and the U.S. have the highest total building weight, the Netherlands and Norway have the highest building weight per capita.
Of the 20 countries projected to have the highest material demand between now and 2050, 19 are low- or middle-income nations. The U.S. is the lone exception and is the only high-income country projected to have its population grow over the next 25 years.
"This study provides new insights into what sustainable cities of the future should look like," said co-author Benjamin Goldstein , assistant professor at SEAS. "Now the challenge is to make it happen."
While the study reveals important new considerations for optimizing materials use, builders and city planners will have to weigh those against the potentially competing goal of land use optimization, Song said. For example, although taller buildings use more steel than shorter buildings, they can also accommodate more people within a city's existing footprint, which may be more desirable or necessary.
This research was funded by the National Natural Science Foundation of China, Ministry of Education of China, Independent Research Fund Denmark and RurbanClimate Danida.
