The architect who promotes flooding to solve the water crisis
This article is adapted from Erica Gies' book 'Water Always Wins: Thriving in an Age of Drought and Deluge', available in slowwater.world.
Yu is at the forefront of a movement that aims to restore the ebb and flow of water in urban environments. His landscape architecture firm Turenscape, which he co-founded in 1998, creates flexible spaces for water to spread and seep underground, both to prevent flooding and to store it for later use.
His vision is to heal the natural hydrology that we have interrupted by limiting rivers with dikes, placing buildings or parking lots in the places where water wants to pass, or erecting dams that, to varying degrees, dried up 333 rivers in the Yangtze River area (China). By trying to solve each problem separately (floods, on the one hand, water scarcity on the other), the twentieth-century approach to water management has undermined itself. "The drainage is separate from the water supply; flood control is separate from drought resistance," he wrote in 2016 for a paper he presented at a Harvard University symposium.
Since the early eighteenth century, we have filled or drained up to 87% of the world's wetlands, which would otherwise absorb and release water flexibly. It's a key reason why urban flooding is more prevalent around the world: As populations grow and cities expand, builders pave floodplains and farmland, cut down forests and channel rivers, leaving stormwater that once seeped into the ground with nowhere to go. The ground lost to city building has doubled worldwide since 1992. When a city increases the area of roads, sidewalks or parking lots by 1%, stormwater runoff increases the magnitude of annual flooding in nearby waterways by 3.3%.
In densely populated cities, only about 20% of the rain infiltrates the ground, the rest goes down drains and pipes, something that for Yu is crazy in places with water shortages.
We have already begun to see the impact on the water cycle. The summer and fall of 2021 brought deadly flooding to the US, Germany, Belgium, India, Thailand and the Philippines. At the same time, drought, crop failures and wildfires ravaged the western United States, Syria, Guatemala, Greece and Siberia. Global economic losses from floods rose from €441 million per year, on average in the 1980s, to €67.097 billion in 2020.
When it comes to drought, more than 2 billion people worldwide already live with severe or high water insecurity. Researchers predict that as global warming continues, two-thirds of the world's population, more than 5.25 billion people, will experience worsening and more frequent drought conditions.
These recent disasters have shown many people the truth of what climate scientists have been saying for years: climate change is a water-related change.
Sponge cities are part of a global movement that goes by several names: green infrastructure in Europe, low-impact development in the United States, water-sensitive urban design in Australia, natural infrastructure in Peru, nature-based solutions in Canada. In contrast to industrial management, in which people confine water with dikes, canals, and asphalt and push it off land as quickly as possible, these more recent approaches seek to reclaim the natural tendency of water to remain in wetlands and floodplains.
Because of that common denominator, I've come to think of them collectively as the "Slow Water" movement. As in the Slow Food movement, the solutions are adapted to the ecology, climate and local people. Slow Water's most ambitious projects involve the conservation or restoration of wetlands, river floodplains and mountain forests, simultaneously safeguarding carbon storage and protecting homes from endangered plants and animals. But there are also small urban projects, wedged between buildings or in narrow corridors along the streets.
It has turned Turenscape into an empire, with 600 employees in three offices. The company has more than 640 completed or ongoing projects in 250 Chinese cities and 10 other countries. Turenscape also publishes the journal Landscape Architecture Frontiers, in both Chinese and English, and supports master's, doctoral and postdoctoral students who research hydrology or ecology, or measure the effectiveness of completed projects.
When planning a project, designers must first figure out what the water did before the city was built. In a large clean room in Turenscape's offices, young men and women occupy desks separated by a jungle of plants, concentrated with great attention to that question. They build models of how water behaves within the built environment, taking into account the ecology, geology, hydrology and the specific culture of each place, a kind of computational geography. That data allows Yu and other Slow Water practitioners to model how the reorganization of terrain and available space affects in various ways the way water flows and slows down.
Although Xi's Sponge Cities initiative is based on principles that reflect his own ideas, Yu fears that, in some cases, China is doing it wrong. The country has sometimes used standard solutions for other programs, Yunotes, but for sponge cities to be successful, each project must be site-specific. In his own words, "every patient needs a different solution."
Monsoon rains in China have been heavy in recent summers, challenging not only existing infrastructure, such as dams (several of which have failed or were on the verge), but also the fledgling sponge cities. In the summer of 2021, a pilot project city with a population of around seven million, Zhengzhou (China), suffered significant flooding when more than twenty centimeters of rain fell in an hour and almost 300 people died, leading some to doubt whether the sponge cities were working well.
Zevenbergen notes that designs may need to be modified to better suit local needs. But the most important factor may be that the interventions are simply not ambitious enough. Absorbing 70% of the rain in 13 square kilometers of a city that stretches for 7,500 square kilometers will not prevent flooding. Slow Water projects work best when they can absorb water throughout the landscape, so planners need to think beyond urban territory. A city is part of a larger watershed. Restoring upstream space in natural river floodplains can reduce downstream levels.
Yu is also working this. It is creating a landscape master plan for all of China. In his office, he showed me a series of maps documenting China's elevation, watersheds, flood roads, biodiversity, desertification, ecological security, soil erosion, and cultural heritage. As urbanization spreads, estuaries and deltas settle, as water begins to move differently through landscapes and urban areas, Yu identifies the places where his projects will have the greatest impact.
