China's "sponge city" flood control infrastructure may be inadvertently creating breeding grounds for disease-carrying mosquitoes, according to a perspective published in China CDC Weekly recently.

The article highlights a gap in the country's national standard for climate-resilient urban design, which lacks requirements to manage standing water for vector safety.

Engineers and ecologists broadly agree that sponge city infrastructure is sound in concept. The concern lies not in the idea itself, but in a metrics gap embedded in how such infrastructure is designed and evaluated.

China's national evaluation standard for sponge infrastructure is sophisticated in hydrology. It tracks runoff volume control ratios, pollutant removal and water quality improvement.

However, it lacks attention to biological factors, with no requirement for post-storm dry-down time — the window within which standing water must drain before mosquito larvae can complete their development — and no provision for linking routine inspection findings to vector control responses, according to the perspective.

The warning comes as China's mosquito season began earlier than usual. The white-striped Aedes albopictus, ranked among the world's 100 most invasive species, overwinters as eggs. Its hardened shells can survive cold and drought conditions for months before hatching when conditions improve.

China's National Disease Control and Prevention Administration issued a public warning this spring, saying warming temperatures and increased rainfall have steadily expanded the breeding ranges of Aedes mosquitoes across the country, extending their active season at both ends of the calendar. This year, with Guangdong province experiencing a warm winter and frequent early-spring rainfall, conditions were ripe for an unusually early onset.

"The feeling that there are more mosquitoes is real," said Kang Min, chief expert in infectious disease prevention and control at the Guangdong Provincial Center for Disease Control and Prevention. "But what residents are mostly encountering right now are common household mosquitoes, which overwinter as adults and rebound as soon as temperatures stabilize."

The more concerning species — Aedes albopictus, also known as the "tiger mosquito", which transmits dengue fever and chikungunya — is still increasing.

"We have detected the tiger mosquito in multiple counties and districts," Kang said, "and in some residential areas, vector density is already at very high levels."

The geographic stakes are rising. Dengue fever has historically been confined to tropical and subtropical provinces, but disease ecologists are now tracking what they call "southern disease spreading north".

"The cold season used to function as a natural reset — it could interrupt transmission chains and clear local cases," said Chen Xiaoguang, director of the Institute of Tropical Medicine at Southern Medical University. "If winter becomes too brief for that to happen, an ongoing outbreak can simply carry over into the next season."

Experts at a recent news conference held by the National Disease Control and Prevention Administration said the risk of imported cases of dengue and chikungunya triggering local spread is higher in 2026 than in previous years, and that some areas face a real possibility of clustered outbreaks.

The China CDC Weekly perspective draws on a severe outbreak.

On July 9, Foshan in Guangdong reported a cluster of chikungunya cases. By July 26, the provincial total had reached 4,824 confirmed cases across 12 prefecture-level cities, with 4,754 cases — 98.5 percent of the total — concentrated in Foshan, and 4,208 of those, or 87.2 percent of all provincial cases, clustered in Shunde.

Guangdong's disease control authorities have already taken initial steps. The province has deployed an expanded mosquito monitoring network, including small ovitrap devices bearing the provincial CDC logo, placed in parks, hospital grounds, schools and construction sites. The devices are checked every four days to feed density data into provincial risk models.

Guan Zhongjun, a professor at the Xuanwu Hospital of Capital Medical University and an expert in medical management, said resolving the conflict requires a governance overhaul spanning the entire infrastructure life cycle. "Entomological indicators must be translated into engineering specifications and embedded at each stage — from planning and design through construction acceptance to routine operation and maintenance," Guan said.

In his assessment, responsibilities need to be clearly delineated across agencies. Housing and urban-rural development authorities should update civil engineering codes to mandate physical access to water-holding structures; water resources and municipal maintenance departments should carry out routine clearing after storms; and health agencies should conduct vector impact assessments before the construction of new infrastructure.

The vector-proofing measures would apply to the full range of sponge city assets already embedded in China's urban fabric, including permeable pavements, bioretention basins, rain gardens, constructed wetlands and sunken green spaces. All are designed to hold water and, without proper dry-down standards and maintenance protocols, can serve as mosquito nurseries as readily as they serve as flood buffers, he said.

weiwangyu@chinadaily.com.cn