Sponge city funding explained: central subsidies, PPP bonuses and what cities actually built

Ask a city engineer what a sponge city is and the answer usually begins with green roofs and permeable paving. Ask a finance official and the answer starts with a three-year budget and a competitive defence session. Both are describing the same programme, introduced in China to change how urban stormwater is managed, and the funding design is as instructive as the technology.

The term was first put forward officially in China at the Central Urbanisation Work Conference held in December 2013. The General Office of the State Council then issued the Guiding Opinions on Promoting Sponge City Construction, which called for measures of infiltration, detention, storage, purification, use and drainage so that 70% of rainfall would be absorbed and used on site by 2020.

The 70% number, translated into area

Seventy per cent of rainfall sounds straightforward until someone has to verify it. The practical reading is the annual total runoff control rate, and the Guiding Opinions set it against built-up area: by 2020, more than 20% of the built-up area of cities should meet the target; by 2030, more than 80% should do so. A city with 100 square kilometres of built-up area therefore needs at least 20 square kilometres compliant in 2020, and 80 square kilometres by 2030.

That distinction matters for anyone drafting a plan. The target is not a city-wide average achieved by one showcase district, but a proportion of developed land that must actually function as designed.

How the central subsidy was structured

On 31 December 2014, the Ministry of Finance, the Ministry of Housing and Urban-Rural Development and the Ministry of Water Resources decided to launch pilot projects supported by central government finance. Funds took the form of earmarked subsidies over a fixed three-year period, scaled by city size: 600 million yuan per year for municipalities directly under the central government, 500 million yuan per year for provincial capitals and 400 million yuan per year for other cities. Where the public-private partnership (PPP) model reaches a certain share, a 10% bonus is added to the base amount.

Two further mechanisms kept the programme honest. Cities were selected through competitive review rather than allocation: the three ministries reviewed qualifications, qualifying cities took part in a public defence session, an expert panel conducted on-site review, and results were announced on the spot. Performance was then evaluated on a regular basis, with cities that performed well receiving a bonus of 10% of the central subsidy base and cities with poor results having part of the subsidy recovered.

The pilot list was announced on 2 April 2015. Ranked by regional score, the top 16 cities were, in administrative order, Qian'an, Baicheng, Zhenjiang, Jiaxing, Chizhou, Xiamen, Pingxiang, Jinan, Hebi, Wuhan, Changde, Nanning, Chongqing, Suining, Gui'an New Area and Xixian New Area. On 10 June the Ministry of Housing and Urban-Rural Development added Sanya to the pilot cities for urban dual repair, underground utility tunnels and sponge cities.

Ten measures, four groups

The Guiding Opinions set out ten specific measures in four areas: strengthening planning guidance, coordinating orderly construction, improving supporting policies and ensuring implementation. The ones that change day-to-day practice most are the planning hooks. The annual total runoff control rate becomes a mandatory indicator in urban planning, and a regional stormwater discharge management system is established. Sponge city requirements also become a precondition for planning permission and project approval, enforced at construction drawing review, construction permit and completion acceptance.

From 2015, new urban districts had to fully apply sponge city requirements. Old districts were to combine shantytown and dilapidated housing renovation with action on urban waterlogging, rainwater harvesting and treatment of black and odorous water bodies, moving towards area-wide treatment in which light rain leaves no ponding, heavy rain causes no waterlogging, water bodies are neither black nor odorous and the heat island effect is eased. A project reserve system was meant to avoid wholesale demolition and rebuilding.

The physical measures fall into recognisable categories: sponge buildings and residential areas, sponge roads and squares, drainage and waterlogging facilities, separation of stormwater and sewage, stormwater storage, sponge parks and green spaces that absorb their own rainwater and store or detain rainwater from surrounding areas, plus ecological restoration of urban ponds, rivers, lakes and wetlands. Financing runs alongside: private capital is encouraged to invest and operate, turnkey contracting is used to capture integrated benefits, and local governments are expected to increase funding.

What the comparison countries did differently

Germany's approach rests on the sheer extent and capacity of its sewer networks, which are among the best in the world. Berlin's sewers total about 9,646 km, some of them nearly 140 years old. City centre pipes are mostly combined systems handling sewage and stormwater together, saving underground space; in the suburbs separate systems prevail, which improves the targeting and efficiency of treatment.

Switzerland took the household route from the end of the 20th century with a nationwide rainwater programme. Rather than rebuilding networks, it made small alterations to existing houses: a hole drilled in the wall, a pipe leading rainwater into an indoor storage tank, and a small pump distributing it through the house. Settled and filtered rainwater flushes toilets, scrubs floors, waters plants and even washes clothes, fruit and vegetables. Tax relief and subsidies encouraged uptake.

Singapore, a tropical island with abundant rainfall and rising maximum annual totals over 30 years, keeps urban waterlogging rare through three habits: planning the drainage system in advance, strengthening rainwater conveyance and building large storage reservoirs, and enforcing strict drainage standards for surface buildings.

Los Angeles illustrates the cost of the alternative. In the 1940s the Los Angeles River was turned into a concrete channel to carry floodwater in the rainy season, a 51-mile bathtub between city and sea. Flooding stopped, and the rainwater simply ran away. That is precisely the outcome sponge city construction is designed to avoid, and the reason the target is about absorption rather than conveyance.