What Are Nature-Based Solutions?

Nature-based Solutions (NbS) are actions that work with nature to address societal challenges. The UNDRR defines NbS as actions that “protect, sustainably manage and restore natural or modified ecosystems” to address climate, disaster, and other challenges. Similarly, the UN Environment Assembly describes NbS as measures to “protect, conserve, restore, sustainably use and manage ecosystems” to meet social, economic and environmental goals.

This includes ecosystem-based adaptation (EbA) – using biodiversity and ecosystem services (like forests, wetlands) specifically to help communities adapt to climate change. NbS span a range: from large restored ecosystems (mangrove forests, peatlands) to engineered “green infrastructure” (urban parks, green roofs) and hybrid combinations (e.g. mangroves with small seawalls).

• NbS/EbA: Leveraging forests, wetlands, coral reefs, etc., to buffer climate impacts (floods, heat). Example: reforested watersheds reduce landslide risk and improve water regulation.
• Green/Blue Infrastructure: Engineered or managed natural elements (urban trees, rain gardens, bioswales, constructed wetlands). Also called green infrastructure (GI) for land/vegetation, and blue infrastructure for water systems (ponds, canals). These mimic natural processes in cities or farms.

By contrast, grey infrastructure (dams, seawalls, concrete channels) relies solely on engineered materials. NbS often offer multiple co-benefits (wildlife habitat, recreation, carbon storage) beyond hazard reduction.

Benefits and Evidence for DRR and Adaptation

Flood and Storm Protection: Healthy ecosystems attenuate floods, storms and waves. For example, global analyses show existing mangrove forests avert over $65 billion in flood damage annually and protect 15 million people. Losing these mangroves would increase annual flood damage by ~30% globally. Mangroves can cut wave energy by up to 66% over the first 100 m of forest. Coastal wetlands and coral reefs similarly absorb surge energy, reducing downstream property losses. A World Economic Forum report estimated that protecting coastal wetlands could save insurers $52 billion per year in avoided storm losses.

Water Management: Restoring floodplains, riparian buffers and wetlands slows runoff, reducing flood peaks. In Colombia, 31% of people are landslide-exposed, often due to deforested watersheds. Watershed reforestation is fundamental to cut landslides. In Indonesia and Malaysia, restoring peatlands reduces flood peaks and wildfire haze, improving health and productivity (and one study projects ~66% reduction in haze mortality).

Urban Resilience: In cities, parks and green roofs lower runoff and cool heat islands. Green infrastructure can reduce peak stormwater flows by up to 20–30% in some cities, delaying floods. For example, New York City’s GI program (rain gardens, permeable pavement) manages millions of gallons of stormwater each year, reducing sewage overflows and urban flooding. Green canopies also cut urban temperatures: a mature park can be 2–4°C cooler than paved areas, reducing heatwave impacts on health and energy use.

Drought Mitigation: Healthy catchments improve dry-season water flows. Mangroves and forests improve groundwater recharge. In Kenya, restoring degraded wetlands increased dry-season river flows by ~50%, supporting agriculture.

Quantified Outcomes (selected):

• Mangroves: ~$65B/year flood damage avoided, 15M people protected. Storm attenuation: up to 0.4 m surge reduction per km of forest.
• Coral reefs: Attenuate >90% of wave energy, saving ~$4 billion/yr in storm costs globally.
• Wetlands: Saturated soils store floodwater; studies show restored wetlands can cut downstream floods by 20–40% depending on scale.
• Urban parks: Example: Chicago’s green infrastructure cut combined sewer overflow by 21% in one basin.

These benefits often scale with ecosystem health – dense, well-designed plantings or mature forests yield greater effects.

Case Studies

Coastal Mangrove Restoration (Asia/Florida): Thailand, the Philippines and U.S. Southeast have planted thousands of hectares of mangroves. A study of Florida’s mangroves found they cut Hurricane Irma flood damages by ~25% in mangrove-lined counties (preventing ~$1.5B in direct losses). Restoration in Vietnam’s Can Gio mangrove bay reduced peak storm surge by ~20 cm, protecting Ho Chi Minh City (population 9M).

Urban Green Infrastructure (CLEVER Cities): European cities like London and Hamburg invest in green roofs, walls and parks. The CLEVER Cities initiative (Hamburg, London, Milan) uses urban tree networks to absorb stormwater and combat urban heat. Early monitoring shows reductions in local flood incidents and summer heat stress in pilot areas. For example, London’s green roof projects can capture 50–85% of annual rainfall, reducing runoff.

Watershed Reforestation (Colombia, Haiti): The Andes foothills in Colombia see landslides when forests are cleared. Colombia now integrates forest corridors into its National Adaptation Plan; reforestation in key watersheds is estimated to reduce landslide risk for ~30% of local communities. In Haiti’s Port Salut, UNEP’s Eco-DRR project (2013–16) reforested ridges and shoreline vegetation to reduce storm impacts, pilot-qualitatively improving village safety and demonstrating “ridge-to-reef” risk reduction.

Peatland Restoration (Indonesia): Degraded peatlands cause floods and fires. Indonesia’s peat restoration (blocking drainage canals, rewetting) has begun to lower burn areas; a study projects a 50% drop in burnt area with full restoration, drastically cutting haze and flood risk.

Each case shows how NbS can match context: coastal mangroves for cyclones, urban green for city storms/heat, forests for hillslope stability, peatlands for fire/flood control.

Design & Best Practices

Effective NbS share key principles:

• Science-Based Siting: Use models and risk maps to target areas where ecosystems can block hazards (e.g. wetlands in floodplains, mangroves along storm surge pathways).
• Scale and Connectivity: Large, connected ecosystems (continuous forests, wetland networks) provide more protection than fragmented patches. Plan for ecosystem corridors and sufficient width/area. For example, a 1 km-wide continuous mangrove fringe greatly outperforms scattered patches.
• Stakeholder Engagement: Involve local communities and authorities from planning through maintenance. NbS often depend on local stewardship, so equitably sharing co-benefits (fisheries, recreation) is crucial.
• Multifunctionality: Combine flood control with other ecosystem services. For instance, floodplain wetlands can be managed for both stormwater detention and wildlife habitat (e.g. Florida Everglades).
• Complementary Integration: NbS should complement – not replace – engineered solutions where needed. For example, “building with nature” projects may pair mangroves with dykes for extra protection.

The IUCN Global NbS Standard outlines 8 criteria (societal challenge, biodiversity net gain, resilience, etc.) as best practices for designing NbS projects.

Limitations, Trade-offs and Risks

Nature-based solutions have caveats:

• Time and Permanence: Ecosystem growth is slow. A newly planted forest or wetland may take years before fully functional. In fast-emergencies, NbS alone may not provide immediate protection. Ecosystems also face mortality (drought, disease, fires, sea-level rise) that can abruptly reduce benefits. For example, mangroves can migrate landward under sea-level rise, but overtopping or freshwater loss can degrade them.
• Effectiveness Variability: The protective effect depends on species, density, and context. Not all green spaces equally absorb floodwater. Inconsistent design can yield weak performance.
• Governance & Maintenance: NbS require long-term management (invasive species control, sediment management). Weak governance or land-tenure conflicts can undermine projects.
• Equity and Social Impacts: Without inclusive planning, NbS may benefit some while disadvantaging others. Example: water retention upstream could reduce downstream flows, or mangrove expansion can conflict with fisheries. Care is needed to ensure benefits (e.g. tourism, fisheries) and costs (e.g. land allocation) are shared fairly.
• Maladaptation Risk: Poorly conceived NbS can worsen problems. Planting non-native species or altering drainage without analysis can cause unintended side-effects. The IPCC warns NbS are not a panacea and must be part of broader strategies.
• Financing & Scale: Large NbS often need significant upfront investment before benefits accrue. Private investors may shy away without secure revenue streams or risk guarantees. For instance, coral reef conservation provides storm protection but yields no direct income, making it “hard to monetize”.

Policy and Financing for NbS

To unlock NbS at scale, policy and finance must align:

• Nature-Positive Recovery: Post-disaster rebuilds should integrate NbS (“nature-positive” rebuilding). For example, after Superstorm Sandy, New York incorporated wetlands restoration into its coastal resilience strategy, combining grey levees with marsh restoration.
• Blended Finance: Use public funds, grants or concessional loans to de-risk private investment. The G20’s 2024 sustainable finance agenda highlights blended mechanisms for NbS. Instruments like green bonds, debt-for-nature swaps, and resilience bonds (linking insurance with restoration) can mobilize capital. UNEP estimates ~$133B/year currently flows to NbS (mostly public), but trillions more is needed.
• Insurance Linkages: Insurers are beginning to value NbS. For instance, Wetlands International’s Indonesian project uses insurance incentives for mangrove maintenance. Climate risk transfer can reward NbS: e.g., lower premiums for communities protected by healthy reefs or forests. Research shows intact ecosystems reduce insurance losses.
• Policy Incentives: Governments can embed NbS in planning frameworks (like Sendai DRR or NDCs). 66% of countries now include ecosystem restoration in their climate pledges. Subsidies or tax breaks for green infrastructure (like stormwater utility credits) encourage uptake. Removing perverse subsidies (e.g. for land conversion) is also key.
• Monitoring and Valuation: Rigorous monitoring of NbS outcomes and including ecosystem services in cost-benefit analyses helps justify investments. Incorporating NbS into disaster loss databases and resilience planning makes their benefits visible.

Table: Comparison of NbS types

Type	Typical Benefits	Cost/Challenges	Suitable Contexts
Natural Ecosystems	Highest biodiversity and multiple services; long-term carbon storage; self-sustaining if protected.	Slow to establish; needs space; vulnerable to climate change.	Rural/coastal areas: mangroves for storm coasts, forests for landslides, peatlands for floods.
Engineered Green Infrastructure	Quick installation; targeted functions (e.g. stormwater capture, heat reduction) in limited space; can be cost-effective at small scale.	Lower habitat value; limited scale; maintenance needed (pruning, clearing).	Cities and suburbs: green roofs, rain gardens, bioswales to manage runoff; urban parks for heat.
Hybrid Solutions	Combine strengths (e.g. fish habitat + flood wall); often more resilient than either alone.	Complex design; cost may be higher; requires interdisciplinary planning.	Coastal defense (mangroves + levee), watershed projects (beaver dam analogues + weirs), living shorelines.