New Tool Helps Cities Select and Scale Nature-Based Solutions

As cities try to restore the benefits of natural systems by mimicking how ecosystems function, one option they can use is nature-based solutions (NBS). However, cities often struggle to determine which types of interventions best suit their local context, due to data gaps in how NBS perform and unclear roles and responsibilities for putting them into practice.

WRI’s Cities4Forests and Urban Water Resilience initiatives, with support from the French Development Agency’s (AFD) ECOPRONAT research program — which promotes the development of a pro-nature economy — explored ways to better equip cities with data on flooding, heat and ecological risks, and how NBS can help address these challenges. Working with local partners — the Ethiopian Institute of Architecture, Building Construction and City Development (EiABC) in Addis Ababa and Rwanda Young Water Professionals (RYWP) in Kigali — we tested a new rapid approach to identify climate risks, assess the potential for NBS to respond to those risks and develop strategies for putting them into action. This approach is known as the Strategic NBS Framework.

Helping Cities Prioritize Nature-Based Solutions

City decision-makers rely on data to set planning priorities and guide investments, but gaps in availability, accessibility and accuracy of climate and land-use data can lead to poor decisions. Global datasets offer insights into broader climate and environmental trends but sometimes fail to reflect local complexities. The lack of methods to assess multiple issues — such as flooding, extreme heat and biodiversity loss — together can result in fragmented climate action that addresses problems in isolation.

The Strategic NBS Framework offers a repeatable planning method for rapid spatial risk analysis, helping cities prioritize and invest in NBS to strengthen climate resilience as part of urban planning. It identifies priority areas for intervention based on geographic and environmental risks and helps determine the types of solutions best suited to address current climate risks. For example, greenways, bioswales — long, natural depressions or trenches — and trees not only absorb stormwater and support infiltration but also add shade to reduce heat and provide critical habitat corridors that connect existing green spaces.

This new framework guides cities to:

1. Use a multi-stakeholder approach for analyzing, planning and integrating NBS.
2. Leverage data tools and rapid analysis methods to support decision-making.
3. Identify NBS projects for implementation and establish governance approaches to ensure long-term sustainability.

Applying the Strategic Nature-Based Solutions Framework in Two African Cities

WRI experts combined global and local datasets to evaluate areas in Addis Ababa and Kigali that are vulnerable to extreme flooding and heat, and that also present opportunities to buffer and connect ecological resources. Using a combination of published methods, they quickly produced citywide maps, which were then validated by relevant city stakeholders. This approach reduced both the time and cost of analysis, enabling faster action in priority areas.

Addis Ababa, Ethiopia

Rapid urbanization has significantly altered Addis Ababa’s environmental landscape. Residents are increasingly exposed to rising temperatures and more frequent heat waves, which heighten health risks. Recurrent riverine and flash flooding continue to disrupt livelihoods, damage infrastructure and threaten public safety and well-being. The city's once-rich biodiversity is also under pressure, facing habitat loss along with growing air and water pollution.

Our citywide map identified three priority areas for NBS implementation:

1. The Wallgamo River and surrounding Gurara Hill area (Cluster 3 on the map above)
2. The Gordeme River and surrounding Addis Ketema and Mercato areas (Cluster 1)
3. The downstream areas of the Kebena and Akaki rivers (Cluster 6)

The Addis Ababa Urban Beautification and Green Development Bureau, local government leaders and the project team explored opportunities to integrate NBS into these areas, targeting needs such as heat and flood mitigation, ecosystem conservation, river management and biodiversity restoration.

EiABC designed project concepts to address identified risks in the three priority areas with a mix of green and gray infrastructure solutions: 

• The Gurara Green concept aims to work with local communities and organizations, including Selam Technical School, to restore biodiversity, rehabilitate riverbanks and strengthen agroforestry systems in the Wallgamo River and surrounding Gurara Hill area. It also encourages community participation, especially among vulnerable residents, through a new beekeeping initiative and incentive program.
• The Cooling Mercato concept aims to support the clean-up and greening of the Addis Ketema and Mercato neighborhoods. Through a comprehensive NBS strategy — including introducing reflective materials, tree planting, pocket parks and improved waste management — the project would work with local communities to address the neighborhood's heat risk and the health of the Gordeme River.
• The Akaki Eco concept aims to support rehabilitation of the downstream area of the Kebena and Akaki rivers by working with the city government, local communities and quarrying industries to establish buffer zones and restore quarry sites, helping strengthen the resilience of the area's natural ecosystems.

WRI is in discussions with AFD’s Ethiopia Office and the Addis Ababa Urban Beautification and Green Development Bureau to partner on small demonstrations of the priority area concepts. These initial pilot efforts aim to improve knowledge of NBS implementation and support the city in securing additional funding to continue implementing the development program concepts.

Kigali, Rwanda

Kigali, the capital city of Rwanda — a country affectionately known as the “the land of a thousand hills” — lies in the lower Nyabarongo River watershed, one of the Nile Basin’s seven major tributaries. Heavy rainfall, flooding and landslides frequently cause infrastructure damage, soil erosion, environmental degradation, injuries and fatalities. The city’s rapidly growing population has compounded issues like unplanned or informal settlements, limited affordable housing, encroachment on agricultural land and natural ecosystems, unreliable urban services and unemployment. Local ecosystems face increased habitat degradation, shift in species’ habitat suitability and a loss of tourism revenues.

Our citywide map identified three priority areas for implementing natural-based solutions:

1. The eastern Nyarugenge District and Mpazi River sub-catchment (Cluster 7 in the map above).
2. The Gasabo District and Gatsata-Karuma sub-catchment (Cluster 3).
3. The Kicukiro District and Rubirizi sub-catchment (Cluster 8).

As in Addis Ababa, our local partner, RYWP, developed project concepts to address identified risks in the three priority areas using a mix of green and gray infrastructure solutions:

• The Mpazi-Rugunga concept aims to establish new buffer zones in the Mpazi river, restore forests upstream and plant roadside trees to reduce flood risks and extreme heat in the densely populated eastern Nyarugenge District.
• In Gasabo District, streams in the Gatsata-Karuma sub-catchment lack buffer zones, increasing the impact of seasonal floods. Flood risk is further intensified by heavy pollution from agricultural waste and mining residue from nearby quarries. In densely built-up areas, the Gatsata-Karuma concept aims to launch rainwater harvesting initiatives and tree planting in available areas. In predominantly farming zones, the concept seeks to work with local farmers to introduce sustainable agricultural practices aligned with community needs.
• High population density and heavy traffic contribute to frequent extreme temperatures and flooding in Kicukiro District. The Rubirizi concept aims to establish an urban forest in the upstream area of the Rubirizi catchment to address flood, heat and biodiversity risks. It also seeks to expand sustainable agricultural practices to balance community and ecological needs — preserving wetland habitats for indigenous wildlife and vegetation while creating sustainable income sources for farmers and other local groups.

What’s Next?

WRI is working to improve the Strategic NBS Framework through continued collaboration with AFD and additional cities as part of the Green-Gray Infrastructure Accelerator. Our team is advancing data tools to include additional parameters such as air quality and gender, equity and social inclusion in the framework’s assessment and solution selection processes. In Nairobi, for example, WRI is supporting the Nairobi Rivers Commission in advancing NBS for climate resilience through the Strategic NBS Framework. The planning process is underway and will provide a set of recommended solutions to support communities living along the river.

WRI continues to partner with Addis Ababa and Kigali to develop financial proposals NBS project concepts identified and recommended by EiABC and RYWP. In addition to designing project concepts, institutionalizing NBS in cities requires supportive governance structures and funding to pilot early ideas and expand programs.

In Addis Ababa, WRI and local partners recommend establishing a mayoral steering committee on NBS, along with a dedicated project office and task team to mobilize political, community and financial support. In Kigali, they propose creating a citywide investment program to advance NBS designs, conduct a multi-benefit assessment to support monetization and carry out policy analysis to advance the NBS enabling environment.

Are you or your organization interested in partnering with WRI to implement one of the six proposed nature-based solutions project concepts described in this article? Or are you interested in applying the Strategic NBS Framework in your city? Please reach out to Lisa Beyer or visit WRI’s Green-Gray Infrastructure Accelerator to learn more.