Not All Green Infrastructure Fights Floods Equally, Landmark Basin Study Reveals

When storm clouds gather over China’s Poyang Lake Basin, the difference between a manageable deluge and a damaging flood can hinge on decisions made decades earlier about how the land was developed. A new study published in Natural Hazards has now quantified, with unusual precision, just how unevenly green infrastructure performs across a sprawling urbanizing watershed — and why the answer to safer cities may lie less in how much green space a region builds, and more in exactly where and how it builds it.

The research, led by Hai Sun of the Ocean University of China together with colleagues at Qingdao University of Technology, Clemson University, and Western Sydney University, tackles one of the most persistent blind spots in flood management: the pathways linking land-use patterns to hydrological responses. Urbanization reshapes basin hydrology by replacing soils and vegetation with impervious surfaces such as roads, rooftops, and parking lots. These surfaces prevent infiltration, accelerate runoff generation, and amplify flood peaks, sending more water into rivers faster and overwhelming channels and drainage systems. Green infrastructure — permeable pavements, rain gardens, wetlands, and vegetated storage areas — counteracts this by improving infiltration, storage, and surface roughness. But until now, planners have lacked a rigorous, basin-scale framework for measuring how these benefits vary across space and under different storm conditions.

To close that gap, the team constructed three urban expansion scenarios for the year 2044 in the Poyang Lake Basin: a no-green-infrastructure baseline, a storage-oriented green infrastructure scenario, and a permeability-oriented scenario. The Poyang Lake Basin, China’s largest freshwater lake system and a critical node in the Yangtze River’s hydrology, is a natural laboratory for this question. Its low-lying floodplains, dense tributary network, and rapidly expanding urban platforms make it acutely sensitive to changes in land cover.

Land-use changes under each scenario were simulated using a cellular automaton–Markov (CA–Markov) model, a technique that combines transition probabilities derived from historical land-change data with spatial neighborhood constraints to project how urban footprints evolve. This allowed the researchers to generate realistic maps of where impervious surfaces would spread by 2044 and where green infrastructure would be deployed under each strategy. The hydrological consequences were then evaluated through a coupled one-dimensional and two-dimensional modeling framework, chaining HEC-HMS, a rainfall-runoff model, to HEC-RAS, a river hydraulics and flood inundation model. The coupling is significant: it enables a continuous simulation chain from land-use evolution to runoff generation to flood dynamics, rather than treating each link in isolation.

The baseline results are sobering. Under unconstrained urban expansion, impervious surface coverage in the basin rises from 3.93 percent to 7.37 percent — nearly a doubling of sealed ground. Correspondingly, the basin-averaged curve number, a standard parameter in the Soil Conservation Service runoff method that encapsulates how readily a landscape converts rainfall into runoff, increases from 68 to 72. That seemingly modest shift carries heavy consequences: the researchers calculate an approximately 18 percent decrease in potential maximum retention, the landscape’s capacity to absorb and store rainfall before it becomes floodwater. In plain terms, by mid-century the basin could surrender nearly a fifth of its natural buffering capacity to concrete and asphalt.

Green infrastructure partially blunts this trajectory, but the two strategies do so very differently. Permeability-oriented green infrastructure — designed to restore infiltration across the urban surface — achieves the strongest reduction in impervious coverage, limiting the rise to 6.68 percent, and effectively reverses the degradation of infiltration and storage capacity captured by the curve number. Storage-oriented green infrastructure, which concentrates water retention in discrete facilities, shows only limited improvement in these landscape-scale parameters. The reason is structural: storage works locally, behind berms and inside basins, while permeability works everywhere, beneath every street and rooftop it touches.

Those parameter-level differences propagate directly into flood behavior. Under small to moderate rainfall events, permeability-oriented green infrastructure reduces peak discharge by 6.2 percent and total runoff volume by 3.54 percent, and — critically — it maintains its effectiveness even under extreme conditions, because infiltration capacity does not fill up the way a storage basin does. Storage-oriented measures, by contrast, remain constrained by finite capacity: once a retention facility fills, additional rainfall passes through unattenuated. Yet the picture is not one-sided. The analysis reveals clear spatial heterogeneity: in areas with sufficient storage capacity, storage-based strategies actually outperform infiltration-based measures during large rainfall events, when rainfall intensity outpaces the soil’s ability to absorb water and detention volume becomes the deciding factor. The catch is that this advantage is limited by spatial and capacity constraints at the basin scale — there is simply not enough suitable land and storage volume to deploy it everywhere.

The two-dimensional hydraulic component of the framework sharpens this spatial story further. Permeability-oriented green infrastructure reduces the extent of high-depth and high-velocity flood hotspots, with the strongest benefits concentrated along river corridors and urban platforms — precisely the locations where people and assets cluster. This leads the authors to a practical siting logic built around the curve number itself: boost permeability and roughness on the slopes, maintain them through the channels, and add storage capacity at confluences where flows converge and backwater effects amplify. In other words, read the landscape’s hydrological fingerprints and match the intervention to the terrain.

The study’s most consequential recommendation is that no single strategy suffices. Because green infrastructure performance varies with location, terrain, and storm magnitude, the authors argue for differentiated strategies aimed at residual high-risk areas: infiltration-dominated measures for moderate rainfall, enhanced storage and conveyance capacity for extreme events, and spatially targeted deployment that combines infiltration and storage synergies in low-lying zones, storage-control combinations along flow corridors, and strict land-use regulation in high-risk areas. This is a departure from the one-size-fits-all deployments that have characterized much green infrastructure planning, including China’s high-profile sponge city program, and it provides theoretical support and decision-making guidance for coordinated planning and refined flood risk management at the basin scale.

The timing could hardly be more urgent. Recent global research has documented rapid urban growth inside flood zones since 1985 and projected substantial increases in future fluvial flood risk across China’s major urban agglomerations, with the Global South bearing disproportionately higher exposure. As climate change intensifies extreme rainfall and cities continue to seal their surfaces, the Poyang Lake findings offer a template that travels: simulate the land, couple it to the water, and let the spatial heterogeneity of performance — not generic best practice — dictate where every permeable meter and every storage basin goes. The difference, this research suggests, may be measured not just in percentage points of peak discharge, but in neighborhoods that stay dry.

Subject of Research: Spatial variability in the flood mitigation performance of green infrastructure under future urban expansion in the Poyang Lake Basin

Article Title: Spatial heterogeneity of green infrastructure performance in flood mitigation under urban expansion

Article References: Sun, H., Wang, H., Chu, Y., Yao, W., Fan, C., Chu, Z., & Liang, B. (2026). Spatial heterogeneity of green infrastructure performance in flood mitigation under urban expansion. Natural Hazards, 122(19), Article 637. https://doi.org/10.1007/s11069-026-08312-5

Image Credits: AI Generated

DOI: 10.1007/s11069-026-08312-5

Keywords: green infrastructure, flood mitigation, urban expansion, Poyang Lake Basin, CA-Markov model, HEC-HMS, HEC-RAS, curve number, impervious surfaces, runoff reduction, spatial heterogeneity, flood risk management