"Sponge City Program" and Climate Adaptations

"Sponge City Program" (SCP) was initiated in 2013 during the 13th Five-Year Congress and has been nearly a decade in China. The SCP policy is taking a major step to mitigate urban surface floods (pluvial floods) caused by intensive rainstorms in 30 selected Chinese cities by the Chinese National Government (CNG) in 2014. The first stage of the pilot project has been completed from 2015 - 2018 with the trial construction of Sponge City infrastructure in these "Sponge Cities".

For the positive effect of the SCP, other Chinese cities volunteered to join the program themselves, for example, cities like Guangzhou, Zhengzhou, Hangzhou, etc., which have not been selected in the official batch but also enacted and legislated their own guidelines that coping with the National strategy. The CNG aimed to reduce about 70% of urban runoff and restore/reuse the urban stormwater resources through the SCP by 2030s. The main purpose is targeting to reduce flood risk but also relieve the urban water storage during the dry season that hopefully for the stormwater through "Sponge" infrastructure to purify and reuse these urban water resources for irrigation and recreational purposes. One of the most attractive spotlights of SCP infrastructure and practices is delivering multi-purposes and beneficial to urbanised landscape in most of the Chinese cities. These functions are obvious, for example, largely increasing green spaces and vegetation and soil areas, which can improve the urban ecosystem services and habitats for birds, bees and organisms, but reducing the Heat Islands Effect (HIE) with the shed of trees and providing urban parks for the communities on improving social wellbeing. 

In light of the 27th Conference of the Parties to the United Nations Framework Convention on Climate Change – COP27, China is committed to urban adaptations to address climate change. The Nation is working erroneously hard and focusing on "adaptation" taking up actions to build resilience. The Nation is taking solid actions to mitigate climate impacts, particularly in the Global South and developing countries. The Nation has spent and invested a lot financially in SCP, for example, Nanning in Guangxi Province (one of the major Sponge cities in SW China) spent more than 11 billion RMB (USD $ 1.62 billion at the 2020s rate) and illustrated the commitments and efforts from the National and Municipality governments on the promotion of SCP to address the future climate threats. 

From COP26 to COP27 - urban flood events alarmed

China among other Parties to the Paris Agreement committed to improving climate change adaptation and improving climate resilience to reduce vulnerability. From COP26 to COP27 countries followed the Glasgow Climate Pact, which increased financial investment. 

In fact, the World Meteorological Organization (WMO) reported that weather and water-related hazards caused total damage of USD$ 35.6 billion in Asia alone, these impacts including floods, landslides and drought. Indeed, in the last two years, China has experienced some major urban floods even though the SCP has been invested in and operated well. For example, in the 2021 July 20-21 Zhengzhou flood that the city has been inundated by a 1-in-1000-year event. That translates to the rainstorm 1 hour during the afternoon on 20 July 2021 reaching 203.5mm heavy downpours (that level is 3 times higher than the most severe Black Rainstorm warning level in Hong Kong according to Hong Kong Observatory). The event caused over 300 casualties and cost over USD$21.8 billion in economic losses. A year before in the summer of 2020, Wuhan (another Sponge City) experienced a similar scenario on a record-breaking heavy rainstorm that reached 472.3mm/24hr and caused a severe pluvial flood. Ningbo has also been inundated during the Typhoon In-Fa in 2021 July with over 200mm/24 hr downpours.  

Take home message - SCP is important but more resilient approaches are required

Indeed, the SCP is not a magic bullet, the SCP construction guideline legislated in 2014 by the CNG only required the "Sponge Cities" to equip at 1-in-30 years urban stormwater protection standard and surprisingly many people have not perceived this message well and caused misunderstandings and all events such as Zhengzhou, Wuhan and Ningbo floods discussed above were severely reached from 1-in-50 years up to 1-in-1000 years events. That said, the SCP as same as many Green Infrastructures (GI) worldwide such as Low-Impact Developments is good at addressing mild and small rainstorms and well delivered multiple benefits and many positives have been enhanced. That is not fair to the SCP and GI to carry the guilts and issues on withstanding the climatic extremes as we have to remember the hydrological capacities (i.e., soil-water infiltration rate, soil moisture level and vegetation water) are limited by the natural conditions. 

For this instance, our research team vowed again that the CNG and Municipality government push forward on improving the "soft" measures that put more efforts into using "technologies" such as social media for increasing "communication" on improving the climate "preparation" and "responses". For example, we can track the flood location through social media sources via "WeChat" and "Weibo" (the popular Chinese social media platforms), also can produce more precise analyses via social media news on flood spots and understand the vulnerabilities of communities, for example, that has already been achieved some success in the Greater Bay Area in S China. These measures are encouraged on improving climate resilience under the UN Framework Convention on Climate Change and effectively addressing climate adaptation in terms of addressing flood resilience. 

China will keep moving on improving the SCP to deliver its pledge to climate change adaptation for the urban future. We encouraged the Nation to combine green engineering on the adoption of Green Infrastructure with smart technologies with the climate preparation and responses via "communication" among stakeholders and all actors. The Nation can well use the National mobile networks (i.e., 5G mobile networks and popular internet coverage) and already equipped high technologies with the advanced and "free-of-Charge" and transparent meteorological information platform by the China Metrological Administration (CMA - the official authority for the Met service in China).

These are the advantages and taking the leading role example to address the champion of climate resilience in the Global South. 

Feel Free to read our article at Nature Reviews Earth and Environment (NREE):

Chan, F.K.S., Chen, W.Y., Gu, X. et al. Transformation towards resilient sponge cities in China. Nat Rev Earth Environ 3, 99–101 (2022). https://doi.org/10.1038/s43017-021-00251-y