Many parks, rooftops, and riverbanks emulate the ancient farming technique of terracing, allowing Asian cities to absorb, retain, and purify rainwater.
In 2011, architect Kotchakorn Voraakhom and her family, along with millions of others in Bangkok, lost their homes and became homeless as floods swept through many areas in Thailand, inundating the metropolitan region. This was the worst flood Thailand had experienced in decades, a national disaster lasting over three months that resulted in more than 800 fatalities. Scientists later linked the flooding disaster to increased rainfall driven by human-induced greenhouse gas emissions, according to BBC.
Green Roof of Thammasat University. (Photo: Landprocess).
This disaster shook Voraakhom and prompted her to establish the architectural firm Landprocess. For over a decade, the firm has designed numerous parks, rooftop gardens, and public spaces in low-lying cities to help residents enhance their resilience against flooding. Voraakhom’s most impressive design to date is the green-roofed university building inspired by terraced farming.
At Thammasat University in northern Bangkok, small terrace-like slopes descend from the roof’s peak along Voraakhom’s green roof, allowing the university to collect rainwater and grow food. There are four ponds surrounding the building to collect runoff water. During dry spells, this water is pumped back up using clean energy generated by photovoltaic panels on the roof, which is used for irrigating the terraces. When the roof was constructed in 2019, it became the largest urban rooftop farm in Asia, covering 7,000 square meters of the total 22,000 square meters allocated for organic farming.
Compared to concrete designs, the green roof can reduce the speed of rainwater runoff to the ground by 20 times, a significant issue for Bangkok, according to Voraakhom’s estimates. It also lowers the internal temperature of the building by 2 to 4 degrees Celsius during the hot summer months in Bangkok.
Terraced fields are layered plots created by farmers along hillsides and mountains to maximize land use. This type of farming is common in many Asian countries, including China, Japan, Thailand, Vietnam, and the Philippines. Their origins can be traced back to the Yangtze River basin in China over 5,000 years ago.
Despite their varied shapes and sizes, all terraced fields are designed to follow natural contours, allowing for the collection and retention of rainwater while using that water to nourish the soil and crops. According to Yu Kongjian, a professor of architecture at Peking University in China, the terracing techniques of generations of farmers could provide significant benefits for Asian cities dealing with heavy rains.
Terraced fields are fundamental to Yu’s theory of sponge cities, which calls for cities to rely on land and greenery instead of steel and concrete to address flooding and excess rainfall. He advocates for rainwater to be absorbed and retained at its source, slowing down its flow and controlling where it drains. Terraced fields help mitigate flooding at the source. Since 1997, Yu has designed over 500 sponge city projects incorporating terraced elements across China, some of which have made a remarkable impact.
For instance, the Yanweizhou Park, completed in 2014 in Jinhua, Zhejiang, Yu’s hometown, features riverbanks resembling terraced fields planted with grass that can adapt to aquatic environments. This “sponge” characteristic can reduce the park’s maximum annual flood levels by up to 63% compared to concrete structures.
