Zhengzhou, China (national Sponge City Program)
#00193
Case study of
#00009 Catchment-wide rain gardens and sustainable drainage to cut runoff at source
Implementer
Chinese national government Sponge City Program (30 pilot cities from 2015), including Zhengzhou municipal government
Timeline
Since Jan 1, 2015
Location
Description
China's Sponge City Program launched in 2015 with 30 pilot cities and over RMB 1 trillion (~140 billion USD) in cumulative national spending, deploying permeable surfaces, rain gardens and green infrastructure at scale. Zhengzhou, one of the pilot cities, illustrates the program's design ceiling: on 20 July 2021 it received 201.9 mm of rain in a single hour — far beyond the ~1-in-30-year storm envelope that sponge infrastructure is designed for. The State Council investigation recorded 380 deaths and 20.9 billion USD in damage, and found officials had withheld death reports. The program delivered real cooling and routine-stormwater benefits, but was marketed as flood-proofing without disclosing design limits, which suppressed evacuation behaviour.
Metrics
6Funding
Lessons learned
- Publish the return-period design limits of green drainage infrastructure publicly so that residents and officials understand what rainfall magnitudes it cannot handle — sponge infrastructure is designed for roughly 1-in-30-year storms, not extreme events like 201.9 mm/hour.
- Pair green infrastructure with grey infrastructure, early-warning systems and evacuation protocols; nature-based drainage alone cannot substitute for emergency response at extreme return periods.
- Separate accounting of co-benefits (cooling, livability, routine stormwater) from flood-protection claims avoids overselling and allows honest evaluation of each benefit independently.
- Suppressing casualty information (as found by the State Council investigation) destroys the public trust that emergency response depends on; transparent reporting is an operational prerequisite, not an afterthought.
Documented Jul 24, 2026