The Nature-Based Solutions Opportunity Scan

Leveraging earth observation data to identify investment opportunities in NBS for climate resilience around the globe
 

The Challenge 

More than half of the world's population lives in cities, and that number is rising every day. Urban areas are becoming more crowded, corrosively reducing green spaces within cities, and causing loss of biodiversity, and in turn, affecting people’s mental and physical well-being and exposure to disaster impacts. At the same time, cities are facing growing climate-related challenges. Climate change and urbanization are exacerbating disaster risks, and these risks are affecting the poor and the vulnerable the most. By protecting natural systems and investing in nature-based solutions (NBS), cities have the opportunity to build resilience and protect development gains for future generations. 

NBS for climate resilience are multi-functional solutions to meet the rising challenge of urban resilience.  NBS can provide a range of benefits such as  reducing disaster risks, restoring biodiversity, creating opportunities for recreation, improving human health, ensuring water and food security, and supporting community wellbeing and livelihoods. These investments can utilize a variety of natural features in the urban context, such as creating urban green spaces, protecting or restoring streams and river floodplains, preserving natural wetlands, and creating green corridors. NBS are often integrated into larger investment projects and can complement gray infrastructure to reduce disaster risk and build resilience, while bringing additional benefits. 
 

The World Bank, development partners, and governments are increasingly integrating NBS in their investment portfolios to build climate resilience in cities. While the interest is increasing, World Bank teams and governments often struggle to identify project sites and types of NBS for climate resilience that can be effective locally, particularly in data-poor environments. There is a need for a quick and robust analytical approach that can support the initial identification of opportunity areas for investment in NBS, relying on globally available geospatial data. Such investment opportunity mapping can inform investment projects in different ways:  

• It supports project identification and is a starting point of an investment plan. 

• It provides a baseline for local stakeholder and community dialogue. 

• And it informs (the design of) (pre-)feasibility studies and designs later in the project.  

Responding to this need, the Global Program on Nature-Based Solutions for Climate Resilience (GPNBS) and the World Bank’s Global Facility for Disaster Reduction and Recovery (GFDRR), have developed the NBS Opportunity Scan (NBSOS).  

What is the NBSOS? 

NBSOS is a geospatial analysis and a participatory process that is offered as an on-demand service for NBS investment opportunity mapping in cities around the world. It aims to support World Bank teams, governments, and other investors to understand which NBS types have most potential in a city, what potential project sites are, what their potential benefits are, and how NBS can complement gray infrastructure. The NBSOS methodology is designed in a way that its deliverables—including results, interpretation, and recommendations, and geospatial data package—can be prepared in approximately six weeks.

 

NBSOS relies on an array of openly available medium resolution (10-to-30-meter) Earth observation data and other geospatial datasets. As shown in Figure 3, the analysis consists of three methodological steps. First, understanding the problem: what is the spatial distribution and magnitude of urban resilience and sustainability challenges and what are the solutions considered? The second step consists of mapping suitable areas for NBS types considered, and the third steps models and estimates the positive impact of NBS to address the identified resilience and sustainability challenges.

Step 1 - Understanding the problem: The objectives and scope of the NBSOS are defined in a consultation process with the project team. In this process, the area of interest is determined, which can vary from a small urban area to a larger catchment around the city of several hundred kilometers squared. The consultation process also identifies the main objectives and typically four or five locally relevant types of NBS interventions are selected from the 14 different NBS types that are described in the Catalogue of Nature-Based Solutions for Urban Resilience (Figure 4).  
 

Priority areas for investment within the city are identified, by looking at where the resilience and sustainability challenges are most prevalent. The NBSOS assesses where people in a given city or area are exposed to flooding, extreme heat, and where people lack health and recreation benefits due to limited availability of public green space (Figure 5).   

Exposure to flooding is calculated as a product of population and annual flood probability based on a global pluvial flood model (Fathom 2020). Using a 30-meter Digital Elevation Model (FABDEM), a downstream catchment area for every pixel is determined to prioritize areas with the highest flood exposure in its downstream catchment. In the case of heat stress, heat exposure is calculated as the product of population and average annual air temperature based on a global temperature model.  Finally, to define areas lacking green spaces that provide health and recreation benefits, the NBSOS calculates the number of people within each sub neighborhood that are not within 300 meters (Konijnendijk, 2022) from a greenspace larger than 1 hectare based on normalized difference vegetation index (NDVI). 
 

Step 2 – Mapping NBS suitability: Suitability maps are created to identify areas for protecting existing NBS and areas that are suitable for creating new NBS (Figure 6) for the selected NBS types (Figure 4). For example, the NBSOS can identify areas with degraded vegetation to determine the extent to which that area can be restored by implementing NBS, such as green corridors, urban forests, or open green spaces. Suitable areas for creating new NBS are mapped for each NBS type, allowing visualization for each of the selected NBS types at the city level.  

NBS suitability is determined by NBS-type specific rulesets using a diverse set of Earth observation indicators that rely on publicly available datasets with global coverage., The indicators include soil properties (ISDA, OpenLandMap), bare soil frequency (Sentinel 2 timeseries), surface water frequency (JRC Global Surface Water), precipitation (CHIRPS), slope (FABDEM), land capability (Sentinel-2 timeseries), land cover (ESA World Cover, Dynamic World), and distance to roads, buildings, and water bodies (Open Street Map).  
 

Step 3 – Modeling NBS benefits: The NBSOS applies index-based valuation of the flood reduction benefits, heat reduction benefits, health and recreation benefits, and other benefits as defined in the Catalogue of NBS for Urban Resilience. These benefits describe the positive impact of the selected types of NBS interventions in the city, and the benefits are estimated for the identified suitable areas for each NBS (Step 2).  

To demonstrate the benefits in spatially explicit way, the models described in Step 1 are utilized to estimate the three main benefits. For instance, the spatial flood mitigation model is used to measure the extent to which the NBS can reduce the exposure of people to stormwater flooding. The heat model estimates the effect of NBS types on air temperature, and how many people in the vicinity of the NBS benefit from this cooling effect.  Finally, the health and recreation benefits of NBS are estimated by the additional population that has access to green space within 300 meters of their homes. The results are presented per NBS as the number of hectares providing high, medium, and low levels of benefit, displayed on the map (Figure 8). This helps demonstrate which NBS type will yield the most benefits and where to implement them to maximize those benefits. 

Other benefits of NBS – such as resources production and biodiversity (Figure 7) – can be valued using a land use matrix-based valuation approach, linking NBS types defined in the Catalogue of NBS for Urban Resilience to a qualitative score of 1 (low) to 3 (high). These benefits are added to the three modeled benefits (flood reduction, heat reduction, and health & recreation) on a case-by-case basis, depending on their relevance locally. Figure 8 shows a generic benefit profile of urban forests. 
 

Optional Step 4: Optimization – Recommendations for NBS investments are provided based on the suitability (step 2) and benefit analyses (step 3). As an optional fourth step in the analysis, an investment plan can be developed using a spatial multicriteria analysis. In practice, suitable areas for NBS interventions such as urban forest, open green spaces, and urban agriculture overlap. However, these NBS interventions will provide different benefits. By assigning weights to the different benefits (e.g., the flood reduction potential is more important than reducing heat), NBS that compete for space can be prioritized. Finally, the NBSOS prioritizes those areas that are most effective in delivering the selected benefits. Figure 8 shows the result of the optimization exercise in Bobo-Dioulasso, Burkina Faso.     

NBSOS is successfully informing World Bank financed investment 

The NBSOS has been successfully implemented in 32 cities in 2022 and 2023 (June 2023), playing a critical role integrating NBS investments into World Bank financed operations. For example, the NBSOS informed the N’Djamena Urban Resilience Project, a US$150 million International Development Association (IDA) investment, by identifying the areas in which NBS could reduce pluvial and fluvial flood risks and address urban heat. Different NBS types were considered to assess which would yield the most benefits to the outlined challenges. During the scan, suitability identification yielded large areas on the outskirts of existing nature that could be protected, and specific areas within the city as suitable for either enhancement or creation of NBS. Benefit modeling then highlighted which type of NBS could mitigate flooding, runoff, and heat. The creation or restoration of urban green spaces, including for urban farming, and river floodplains were as determined as the NBS types with the highest potential for reducing risks. 

Additionally, in the Democratic Republic of the Congo, the NBSOS was part of a technical study to identify NBS investment opportunities for low carbon development and urban resilience in the city of Kinshasa. The study, with support from the Gap Fund, informed the integration of NBS under planned investments of the Kinshasa Multisector Development and Urban Resilience Project, a US$500 million IDA investment. The scan identified potential locations and suitable NBS types in the city, including the creation and restoration of urban forests, green corridors, and green roofs as effective methods to address erosion, flood risks, and heat island effects. The study was unique in that it recommended suitable plant species for the identified NBS by the NBSOS and accounted for carbon sequestration benefits of the potential NBS. 

By identifying which NBS were suitable for different locations and calculating the potential benefits, the NBSOS facilitated the integration of NBS into both project designs, contributing to flood and erosion reduction, urban cooling, increased biodiversity, and climate resilience.  

The NBSOS is continually being refined and adapted and will be scaled up to different NBS cases accordingly, based on country demand. This includes the ongoing development of coastal applications of the NBSOS for identifying NBS opportunities along the world’s coastlines.

For additional information about NBSOS, please contact Boris van Zanten (bvanzanten@worldbank.org). 

The Global Program on Nature-based Solutions for Climate Resilience & the Global Facility for Disaster Reduction and Recovery acknowledge support from the European Space Agency for the development of the Nature-based Solutions Opportunity Scan.