What Are Nature-Based Solutions?

Nature-based solutions are actions that protect, restore, or sustainably manage ecosystems in order to address a societal problem while also delivering benefits for biodiversity and human well-being. The category covers wetland restoration for flood attenuation, mangrove and reef conservation for coastal defense, urban tree canopy for heat reduction, and agricultural practices that rebuild soil carbon. What distinguishes them from conventional environmental protection is the explicit engineering intent: the ecosystem is deployed as functional infrastructure against a defined hazard, and its performance is expected to be measured.

The term entered wide use in the 2010s, and its formal definition was settled by the United Nations Environment Assembly in Resolution 5/5, adopted in March 2022. The UNEP overview of nature-based solutions sets out that definition and the conditions attached to it, notably that such actions must address social, economic, and environmental challenges effectively and adaptively rather than substituting for emissions reduction. Environmental management treats the approach as one option in a portfolio that also includes gray infrastructure and hybrid designs combining the two.

Standards and Design Criteria

Because the label attracted projects of uneven quality, verification frameworks followed quickly. The IUCN Global Standard for Nature-based Solutions provides eight criteria with 27 associated indicators, covering societal challenge, scale of design, biodiversity net gain, economic viability, governance, trade-off balance, adaptive management, and sustainability of the intervention. The standard was developed through consultation with more than 800 practitioners across over 100 countries, and it functions as a self-assessment tool that scores a project against each indicator rather than as a pass-fail certification. Applying it forces designers to state the hazard being managed, the ecological baseline, and the monitoring plan before construction, which is the same discipline expected of engineered works.

Green and Hybrid Infrastructure

In the built environment, the approach most often takes the form of green infrastructure that manages stormwater at its source. Bioswales, permeable pavement, constructed wetlands, and green roofs infiltrate or detain runoff that would otherwise overwhelm combined sewers, and the EPA's green infrastructure program documents design guidance and municipal cost comparisons against pipe-and-basin alternatives. Coastal work follows a parallel logic: restored oyster reefs and salt marshes dissipate wave energy ahead of a seawall, reducing the crest height and maintenance the hard structure requires. Hybrid designs of this kind are common because living systems provide graded protection that degrades gracefully, while engineered elements supply a guaranteed minimum under design-storm conditions.

Measurement and Uncertainty

Quantifying performance is the persistent technical difficulty. Flood attenuation from an upstream wetland depends on antecedent soil moisture, storm duration, and catchment geometry, so a single design coefficient rarely transfers between sites. Carbon accounting faces a similar issue: soil and biomass carbon stocks must be measured against a counterfactual baseline, monitored over decades, and discounted for reversal risk from fire, disease, or land use change. Remote sensing, eddy covariance flux towers, distributed soil moisture sensors, and hydrodynamic models are the main instruments for closing these gaps, and long monitoring records are what allow a project to be credited rather than merely claimed.

Applications

Nature-based solutions are applied across many fields, including:

• Urban stormwater management and combined sewer overflow reduction
• Coastal protection and shoreline erosion control
• Urban heat island mitigation through canopy and green roofs
• Watershed management for drinking water supply and quality
• Carbon sequestration in forests, soils, and coastal wetlands
• Agricultural resilience, including agroforestry and cover cropping
• Disaster risk reduction planning for floods, landslides, and drought