What are Nature-Based Resilience Solutions?
Natural and nature-based resilience solutions (NNB; also known as green infrastructure, gray-green infrastructure, ecosystem-based management, engineering with nature) leverage natural features, systems, and processes (e.g. wetlands, trees, floodplains, groundwater infiltration) to address issues that are often dealt with using gray infrastructure (e.g. stormwater treatment, protection from flooding and landslides, erosion control). They can be designed to reduce risks from extreme events such as heat waves and storms, limit air and water pollution, lower costs (construction, operations and maintenance), increase adaptability, increase visual appeal (e.g. green walls and roofs), and even to reduce food insecurity (e.g. growing food on green roofs or walls).
Nature-based infrastructure includes smaller-scale approaches such as green roofs and walls, rain gardens, bioswales, urban tree canopies, and permeable pavements; as well as larger-scale natural infrastructure features such as wetlands, marshes, riparian buffers, coastal dunes, and functioning floodplains.
In some cases, green infrastructure can accomplish things that are impractical using grey infrastructure. For example the rate of sea level rise at a local level could be limited by increasing coastal accretion (e.g. restoring natural sediment flows to the coast by removing dams and shoreline hardening, through restoring coastal wetlands, mangroves, and marshes that capture sediment), limiting erosion (e.g. restoring oyster and coral reefs that limit erosion of sediment from the coast, restoring floodplains to limit strength of floodwaters), and/or reducing land sinking due to aquifer over-withdrawal (e.g. increasing groundwater and aquifer recharge).
How do Nature-Based Resilience Solutions work?
Green and gray-green infrastructure projects can focus on:
- Preserving intact systems such as preventing new development along coastlines, in floodplains, and in other hazard-prone areas.
- Restoring degraded systems to enhance their ability to reduce climate risk, for example by restoring wetlands in floodplains or replanting forests to reduce erosion, drought, and heat waves
- Mixed approaches such as using permeable pavement and rain gardens to increase groundwater recharge, reduce flood intensity, and limit toxic runoff, or planting trees and installing green roofs on buildings in areas prone to extreme heat.
Federal approaches to promoting natural and nature-based approaches include:
- Creating new and strengthening existing rules. For example, communities seeking protection under the National Flood Insurance Program could be required to include an analysis of flood risk mitigation potential of natural infrastructure in their Flood Hazard Mitigation Plan. The Coastal Barrier Resource System map could accommodate shoreline migration by using sea level rise projections to include open spaces not currently in the immediate coastal zone. Building codes could be updated to support the use of natural infrastructure and green building practices.
- Lowering financial and administrative barriers. This could be increasing funding for existing NNB-focused programs such as NOAA’s Living Shorelines grant program, or for NNB approaches within broader funding programs such as HUD Block Grants or USDA’s Urban Agriculture and Innovation program. Revolving loan fund and grant program to help cash-strapped communities invest in resilience with emphasis on NNB. Given the state of the nation’s water and transportation infrastructure, an opportunity for a big win-win is to use NNB approaches to help meet the infrastructure investment gap in ways that increase long-term cost-effectiveness and provide lots of other benefits such as social, economic, and environmental.
- Incorporating NNB in accounting and evaluation practices. For example, federal agencies could be required to give full consideration to the use of NNB infrastructure and solutions to reduce flood damages, using existing rates to value the decrease in flood volumes. Cost-benefit and related analyses for federal investments could be update to account for financial and non-financial impacts (see example below), and to account for differences in life-cycle expenditures for and vulnerability of grey vs. green infrastructure.
Key design considerations
How much to focus on dedicated natural or nature-based project funding, versus promoting its incorporation into existing funding mechanisms, versus melding funding streams (e.g., combining conservation and infrastructure funding)?
Is the greatest benefit for the project or programmatic mission through restoration of degraded systems, protection of intact systems, or creating “gray-green” systems?
At the implementation level, green infrastructure is a relatively well-developed area of practice. The Army Corps’ Engineering with Nature Initiative has created a two-volume atlas of natural or nature-based infrastructure projects addressing a diversity of climate-related risks.
At the regulatory level, the 2014 Principles, Requirements, and Guidelines (PR&G) for federal investments in water resources are a good example of incorporating green infrastructure into federal decision-making. They require evaluation and documentation of non-monetary as well as monetary costs and benefits, including explicitly accounting for ecosystem services using categories based on the 2005 Millennium Assessment. They also require that alternatives be evaluated relative to their contributions to the federal objective and guiding principles: healthy and resilient ecosystems, sustainable economic development, floodplains, public safety, environmental justice, and a watershed approach. There must be full disclosure of trade-offs and a documented rationale for selecting the preferred alternative given the tradeoffs. Each agency is required to update its procedure as needed to apply the new PR&G to their agency-specific missions. The 2017 USDA manual on how to analyze federal investments in water resources is a good example of this.
Federal funding sources for green infrastructure include:
- Community Reinvestment Act
- CDC Community Health Assessments & Health Improvement Plans
- Clean Water State Revolving Funds
- Section 319 Grant Program
- FEMA National Flood Insurance Program Community Rating System
- Congestion Mitigation and Air Quality Improvement (CMAQ) Program
- Recreational Trails Program
- Transportation Alternatives Program
- HUD Community Development Block Grant Program
- NPS Land and Water Conservation Fund
- S. Army Corps of Engineers
- S .DOT Transportation Investment Generating Economic Recovery (TIGER) Program
- Natural Resources Conservation Service
- USFS National Urban and Community Forestry Advisory Council (NUCFAC)
- USFWS Endangered Species Act
American Rivers, American Society of Landscape Architects, ECONorthwest, and Water Environment Federation. 2012. Banking on Green: A Look at How Green Infrastructure Can Save Municipalities Money and Provide Economic Benefits Community-Wide.
FEMA’s Coastal Barrier Resources System page: https://www.fema.gov/coastal-barrier-resources-system
Georgetown Climate Center Green Infrastructure Toolkit: https://www.georgetownclimate.org/adaptation/toolkits/green-infrastructure-toolkit/introduction.html
NOAA Habitat Blueprint Living Shorelines: https://www.habitatblueprint.noaa.gov/living-shorelines/
The Civic Federation. 2007. Managing Urban Stormwater with Green Infrastructure: Case Studies of Five U.S. Local Governments.; Milwaukee Metropolitan Sewerage District (MMSD). 2013. Regional Green Infrastructure Plan.