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Trees in the jungle
Natural Environment

Drought and flood: Harnessing nature to fight climate risk – Part 2

Nature-based infrastructure assets are cleaner and more adaptable than grey infrastructure equivalents, and equally economically viable too. They do, though, pose a number of inherent challenges.

Organisation for Economic Co-operation and Development (OECD)
10 August 2021

Nature-based solutions (NbS) have fundamental characteristics and requirements which differentiate them from grey infrastructure, such as long timescales until intended benefits develop, large spatial scales, dynamic uncertainty, and diffused benefits. These characteristics can lead to NbS being a “bad fit” for decision making within institutional, regulatory and financial processes that have all been developed with grey infrastructure in mind. Traditional enabling environments (institutional, regulatory and financial) can therefore inadvertently discourage the use of NbS.

While NbS do not always emerge through traditional enabling environments for reasons discussed below, some of the unique characteristics of NbS are well suited to recovery measures. For example, while it can take longer for the full intended benefits of an NbS to materialize (such as decreased erosion and improved water quality), their initial steps, such as restoration, can be quick to implement requirements. In addition, while it can be difficult to measure (and capture) co-benefits, the ability of NbS to achieve multiple policy goals with one intervention can make them particularly appealing public investments.

Time scales

Some NbS, especially those involving the restoration of badly degraded ecosystems, can be slow to develop their adaptation benefits or deliver potential co-benefits in full. While grey infrastructure assets reach their desired protective benefit immediately upon finalisation of construction, the growth rate of the living NbS components, such as forests, takes much longer to fully reap their protective benefit. At the same time, the adaptability of NbS over time make them appreciate in value as opposed to the high depreciation costs associated with grey infrastructure. The challenge though is that NbS may not yield the risk reduction effects in the time frame policy makers would hope for.

Spatial scales

The spatial scale considered for planning NbS substantially affects their ability to deliver expected outcomes. The integrity and health of ecosystems at landscape scales determine the potential of NbS to be effective, as ecosystems are highly dependent on the larger enabling environmental processes. For example, the alteration of upstream sediment loads may influence downstream coastline stability, which in turn determines the success and feasibility of downstream or coastal interventions. Often, NbS cannot be sustained by managing individual sites in isolation, as the delivery of associated ecosystem services might depend on processes taking place on a larger scale. In some cases, a certain size of ecosystem may be needed for it to be resilient to various pressures and therefore continue to provide services in future. However, the appropriate scale is unique to each NbS. For example, empirical evidence suggests that natural water retention measures can be effective in small catchments, but may not have the same effectiveness when up-scaled to larger areas. Finally, there are inherent trade-offs in the use of NbS as the space dedicated to NbS often implies the land cannot be used for another productive use.

Performance reliability

Ecosystems are not static, as they are made of living components that change over time. This can be a benefit, as it means NbS can adapt to changing environmental and risk conditions, thereby potentially exceeding the design lifetime of grey infrastructure. However, the dynamism of NbS also introduces new sources of uncertainty, which can increase the difficulty in developing solid predictions about the level of service provided. NbS implemented for climate adaptation purposes may themselves be climate-sensitive. However, the Intergovernmental Panel on Climate Change (IPCC) Special Report on Global Warming of 1.5°C found that 70-90% of coral reefs would be lost if the temperature increased to 1.5°C, and more than 99% if temperature increased by 2°C. Peatlands, as another example, provide valuable ecosystem services through flood management and carbon sequestration, but are highly sensitive to climatic change. Therefore, the success of NbS can only be achieved by ensuring management and restoration approaches take into account anticipated climate impacts as well as the tolerance of ecosystems to these impacts.

Ecosystems are not static, they are made of living components that change over time. This can be a benefit – it means nature-based solutions can adapt to changing environmental and risk conditions, thereby exceeding the design lifetime of grey infrastructure. However, their dynamism also introduces new sources of uncertainty.

Quantification of benefits

In addition to their primary purpose, NbS generate ancillary social, economic and environmental co-benefits related to human health and livelihoods, food and energy security, ecosystem rehabilitation and maintenance, climate adaptation and resilience, and biodiversity. While these co-benefits can be of great interest to the general public, the government and affected communities, they are often not reflected in the benefits assessment of traditional infrastructure investments. The existing methods for assessing, valuing and monitoring these co-benefits are often underdeveloped or challenging to apply.

This article is excerpted from the OECD policy paper: Nature-based solutions for adapting to water-related climate risks

Download the full report here