5,000-Year-Old Rice Terraces Inspire Asian Architects in Designing Modern Flood Control Systems

Growing up in Bangkok in the 1980s, one of the Thai landscape architect Kotchakorn Voraakhom’s most memorable moments was playing in floodwaters in a small boat built by her father in front of her home. She recalls not needing to go to school during those days, saying “I was so happy that I didn’t need to go to school because we didn’t know how to get to it.”

Nearly 30 years later, the flooding turned from a fun childhood recollection to a devastating experience when in 2011, millions of people in Bangkok, Voraakhom, and her family were displaced and became homeless due to the floods that plowed through all over Thailand. It was the country’s worst flood in decades, becoming a nationwide disaster that lasted more than three months and killed more than 800 people. Scientists link the flooding to increased rainfall triggered by human-caused greenhouse gas emissions.

The incident deeply affected Voraakhom, and with that experience, she founded her own landscape architecture firm Landprocess. Over the past decade, Landprocess has designed parks, rooftop gardens, and public places in and around the low-lying city to help its people increase their resilience to flooding.

One of Voraakhom’s most intriguing designs is an enormous university roof inspired by rice terraces, a traditional form of agriculture practiced in Asia for around 5,000 years.

Voraakhom’s design is only one part of a wider trend in Asia that is seeing architects take inspiration from rice terraces and other agricultural heritages to aid urban communities in reducing waterlogging and flooding.

Thammasat University, located in the north of Bangkok, has tiers of small paddy fields cascading down from the top of the building along Voraakhom’s green roof, allowing the campus to collect rainwater and grow food. Four ponds around the building catch and hold the water flowing down. On dry days, this water is pumped back up using the clean energy generated by the solar panels on the roof and used to irrigate the rooftop paddy fields.

The roof, built in 2019, became Asia’s largest urban rooftop farm with 7,000 sq m (75,000 sq ft) of its total 22,000 sq m (237,000 sq ft) dedicated to organic farming. According to Voraakhom, the fall of the runoff — excess rainwater that flows to the ground, which is a big problem for Bangkok — can be slowed down by the green roof by about 20 times. She also says that the roof can lower the temperature inside the building by 2-4C during Bangkok’s hot summers.

Rice terraces are layer upon layer of paddy fields usually created by farmers along the sides of hills and mountains to maximize the use of land. Their origins trace back to the Yangtze River Basin in China more than 5,000 years ago, and today, they can be found in many Asian countries including China, Japan, Thailand, Vietnam, and the Philippines. Their sizes and shapes may vary but all rice terraces are built to follow natural contour lines, meaning that each layer has equal elevation above sea level. This enables them to collect and hold rain and use it to nurture soil and crops.

According to Yu Kongjian, designer of China’s “sponge city” concept and professor of landscape architecture at Peking University in Beijing, the indigenous know-how of creating rice terraces can hugely benefit Asian cities when it comes to handling rainstorms. Chinese cities, and many others in Asia, have a monsoon climate characterized by rainy summers and drier winters. They can get up to a third of their annual rainfall within a day. Yu argues that the huge downpours mean that flood-control measures in those cities need to be based on localized ways of adaptation tested and proven over thousands of years.

Yu centered his spongy city on the use of rice terraces to solve flooding and excess rainfall problems. According to him, rainwater should be absorbed and retained at the source, slowed down in its flow, and then adapted to where it ends up. Yu says rice terraces deal with mitigating floods at the source.

Since 1997, he has designed more than 500 “sponge city” projects, including the Yanweizhou Park in Jinhua, China. The park has a rice-terrace-like bank planted with grasses that can adapt to an underwater environment. It is capable of reducing the park’s yearly maximum flood level by up to 63% compared with a concrete one.

The rice terrace design can also filter floodwater that is often contaminated by sewage, chemicals, and other pollutants, as evidenced by Yu’s Shanghai Houtan Park project. The park is situated on a once highly polluted land that used to house a landfill site for industrial waste. Since its establishment in 2009, the park’s terracing element is capable of purifying 800 tonnes of heavily polluted water per day. In one of Yu’s papers published in 2019, he stated that the water in the park now meets the third-category standard for water in China and that it is clear enough for fish to live in.

The terracing trend has also sprouted in Vietnam, with Hanoi-based firm H&P Architects headed by Doan Thanh Ha combining traditional and agricultural wisdom with eco-friendly buildings. According to Doan, “The terraced rice fields in Vietnam are an example of local knowledge that carries a deep understanding of natural laws, particularly those of water. This kind of local knowledge can also play a ‘significant role’ in helping modern communities maintain biodiversity and ecosystems, as well as responding to climate change.”

Yu agrees, stating that the use of terraced rice fields could even be transplanted to cities like London. “Any slope or slanting surface can be turned into nature-filled terraces to absorb rainwater,” he said.

Numerous Asian cities have started rethinking their rainwater management strategies in recent years due to increasing urbanization and climate change. Monsoon downpours are getting more intense in many places. Typhoons are becoming more destructive and sea levels are rising as well. Some cities such as Jakarta and Ho Chi Minh City are also sinking rapidly due to the loss of groundwater.

Lei Yanhui, a teaching fellow of urban planning and design at the Xi’an Jiaotong-Liverpool University in Suzhou, China, says that in many of these Asian cities, rainwater cannot penetrate the paved surfaces. This means that the soil underneath does not have the chance to soak up and store rainwater to contribute to the natural water cycle system. Furthermore, some cities’ drainage systems do not separate rainwater from sewage and are prone to overloading and overflowing during storms.

Extreme downpours flooded Beijing in the summer of 2012, a year after Thailand’s massive flooding, resulting in a record-breaking 460mm of rain in just 18 hours. The incident caused 79 deaths and around USD 1.6 billion in damages. Shao Zhiyu, a professor of urban flood control at Chongqing University in southwest China, stated that the crisis marked a watershed moment, “After that, China started to pay proper attention to [urban] rainwater drainage and flood prevention.”

China officially adopted the “sponge city” concept as a national program in 2014, with 16 cities chosen as “pilots” in the following year to try out the model. The program included Chongqing, a mountainous megacity located in central China with a population of 32 million.

Shao has a background in engineering and was a member of the team tasked to design a “spongy” new riverside area in Chongqing that includes plant-filled terraces on slopes. He says, “We used to think that we should control floods. But now we have realized that floods cannot be controlled but [have to be] adapted to because the power of nature is too great. The design was initially intended to purify rainwater before it flows into the river, but it is also capable of reducing the peak flood level, as long as the rainfall is not too extreme.”

For Voraakhom, rice terraces are a reminder of the simple yet adaptive lifestyle of her ancestors who lived in harmony with water and seasonal changes for millennia. Bangkok, situated 1.5m (4.9ft) above sea level, only has seven sq m (76.3 sq ft) of public green space per capita, which is one of the lowest amounts in Asia. The city hadn’t built a single new public park for 30 years until the Chulalongkorn Centenary Park, designed by Voraakhom with flood retention elements, opened. “Building urban resilience is the only way [for us] to survive,” says Voraakhom.

As nature-based solutions gain more attention, there have been debates over whether they can really handle more and more relentless storms compared with more conventional “gray” infrastructure such as dams and pipes. Professor of Engineering at the Hong Kong Polytechnic University Wang Yuhong thinks that green infrastructure can be a “meaningful supplement” to gray infrastructure if applied to suitable geographies.

He says that designs based on rice terraces could benefit cities with mountains, such as Hong Kong, where rainwater can wash down steep slopes rapidly. Hong Kong has built a huge concrete tunnel to intercept rainwater at mid-levels of the island and drain it into the sea to prevent the city center from being inundated.

“But this rain-collecting method is expensive,” Wang says. Completed in 2012, the project cost nearly HKD 3.9 billion. “If we copy the rice-terrace principle, we can retain the rainwater in the mid-levels in different ways, such as by building rain gardens. For many cities, this would be a more economical method.”

Still, the idea could be too costly, technically challenging, and emissions-intensive in some places. Wang notes that bringing any kind of green infrastructure to the world’s densest cities won’t be easy. “Asian cities are compact, therefore it is very hard to find large enough spaces to act as ‘sponges’ to take in floodwaters,” according to Wang.

A more effective way is to build massive underground vaults to store stormwater as Hong Kong and Tokyo have done. Lei points out that artificial facilities such as underground storage tanks have drawbacks, “They are isolated and cannot help much in establishing a natural rainwater recycle system the same as [those based on] rice terraces.”

Shao says that green infrastructure can show obvious effects in flattening peak flood levels for the types of high rainfalls seen once every three to five years. “But for more severe [storms], such as those that occur once in ten years or more, we still need to rely on grey infrastructure, such as urban drainage, pump stations, and flood gates,” she says. Shao does acknowledge that sponge city infrastructure also be combined with other mechanisms to reduce flooding.

For Yu, the sponge city concept is not a total rejection of gray infrastructure. According to him, cities should prioritize using green infrastructure but if it is really impossible, “then we can use pipes.”

Many agree that cities need to take a page out of their ancestors’ experience in adapting to the natural world and its changes. Yu states, “Instead of fearing and blocking floods, humans should “befriend water” to move forward in a more unpredictable climate.” This means cities should redesign their low-lying areas to allow them to be safely flooded during heavy rainfall. The move would not only keep cities’ core functions safe during natural disasters, Yu says, but also establish a natural rainwater recycling system, something the urban concrete jungles of today currently lack.