Africa’s cities, from large metropolises to smaller towns, are increasingly characterized by growing urban sprawl. Kinshasa, Democratic Republic of Congo, is expanding by about 2,000 people and 5 hectares (10 football fields) every day, according to a World Bank estimate. Kumasi, an intermediary city in Ghana, is growing more than 5% every year — at least twice as fast as the capital city, Accra.
As cities and surrounding farmlands expand further into their hinterlands, they encroach upon watersheds essential to water supply and climate resilience.
Watersheds are the natural area of land that drain into a common body of water. The consequences of their degradation are threefold. Without tree cover and healthy soils to absorb rainfall, cities may lose a critical source for groundwater recharge, leading to water shortages. Not only does the quantity of water suffer, so does its quality. Without strong roots to protect and anchor the soil, sediment and the chemicals within it are washed into nearby water bodies, often the primary source for a city’s drinking water. That same runoff can turn into floodwater.
Many cities that once depended on their watersheds for water now face both increasing scarcity and heightened vulnerability to extreme weather. There are, however, nature-based solutions to help alleviate these problems.
Through a combination of upland foresting and urban greening, watershed restoration efforts are starting to deliver positive results in three African cities:
Kigali, Rwanda Plants Trees to Restore the Nyabarango River
By 2050, Kigali is expected to host 3.8 million residents, up more than 200% from 1.7 million in 2022. This growth brings with it growing demand for housing, infrastructure and farmlands, and often comes at the expense of the natural ecosystems that help supply the city’s water.
The heart of Kigali’s watershed is the Nyabarango River, a major tributary of the Nile River that originates in the Nyungwe highlands. As the river approaches the city, once forested areas have become bare and degraded due to people’s growing need for farmland for food and charcoal for cooking and heating. Without natural vegetation to stabilize the landscape, flood risk has increased, as has the risk of deadly landslides.
Restoring tree cover in and near Kigali is essential for stabilizing soil, reducing erosion and improving groundwater recharge. WRI’s SUNCASA project is working with IISD and city and local partners to plant a variety of trees on more than 800 hectares across the city.
Efforts include reforestation (planting new trees in previously forested areas) and afforestation (establishing new forest in previously unforested areas). These trees — all indigenous and many fruit-bearing — increase soil moisture retention, prevent surface runoff and increase biodiversity.
Restoring watersheds isn’t only about planting trees, though. It’s also about building resilient livelihoods and empowering local communities to protect the land. Selected in consultation with local leaders and women’s groups, the new trees offer farmers opportunities to build stronger, more resilient livelihoods by providing fruit, medicine and fodder for their cattle.
These restoration initiatives are taking place in parts of the city that are formally designated as forest and conservation zones under Kigali’s 2050 Master Plan. As the city expands in the next few decades, these areas will remain protected by municipal law and land use regulations.
Dire Dawa, Ethiopia Uses Indigenous Trees to Replenish Groundwater
Dire Dawa is struggling to establish a pathway to water-resilient growth. Home to half a million people, Ethiopia’s second-largest city faces an unprecedented decline in its groundwater levels. Cities and towns along Ethiopia’s eastern corridor, including Haramaya, Aweday and Harar, also depend on Dire Dawa’s groundwater reserves.
Where groundwater resources were once abundant, the city must now dig wells to depths of 600 meters. By 2037, the city’s population is projected to rise by 50%. And with a new Industry Park and Free Trade Zone that began operations in early 2025, the local administration is facing enormous demands on its water resources.
Intensive farming in the upper catchment of the Dechatu river is one of the biggest contributors to the decline in Dire Dawa’s water table. As farmers clear shrubland and forests to make room for coffee and khat , a popular cash crop that’s used as a stimulant, less and less rainwater infiltrates the soil, depleting underground reserves. Once plentiful in Dire Dawa’s watershed, many indigenous acacia trees have been cut down for charcoal and fodder. These degraded landscapes put urban areas downstream at increased risk of flash floods during the rainy season.
The SUNCASA project is rehabilitating more than 800 hectares with local tree species to boost the water supply and prevent flooding. In 2024, more than 125,000 seedlings were planted in previously barren areas to restore critical recharge zones.
In the drylands of the catchment, communities are planting deep-rooting indigenous species like acacia saligna to help rehabilitate barren land. Extremely well-suited to the region’s climate, acacia trees require less water and stabilize the soil.
WRI’s Work Through SUNCASA
Led by WRI and the International Institute for Sustainable Development (IISD) with funding from Global Affairs Canada, the SUNCASA project works with local governments, civil society and community associations to foster climate adaptation, economic growth and sustainability.
By delivering nature-based solutions that restore watersheds, riparian corridors and urban green spaces, SUNCASA’s work is a direct response to climate risks like flooding, heat, landslides and biodiversity loss. By 2027, SUNCASA aims to:
• Rehabilitate more than 2,400 hectares and plant more than 2 million trees across six critical micro-catchments in Kigali, Rwanda;
• Plant more than 1.3 million trees over more than 800 hectares in Dire Dawa, Ethiopia; and
• Restore more than 450 hectares and plant 46,000 trees in strategic sites across Johannesburg, South Africa.
These interventions are designed to center the needs of vulnerable communities while ensuring that cities can continue to rely on their water systems. Gender and social inclusion are core tenets of SUNCASA’s work. Ultimately, the project aims to benefit 2.2 million people, directly and indirectly, by increasing their resilience to climate risk. SUNCASA will also train and support more than 22,000 individuals involved in the project’s implementation.
Local partners include: the city of Kigali, ARCOS Network, AVEGA-Agahozo, and the Rwanda Young Water Professionals in Kigali; the Dire Dawa administration, Hararghe Catholic Secretariat and Haramaya University in Dire Dawa; the city of Johannesburg, Johannesburg City Parks and Zoo, the Johannesburg Inner City Partnership, Zutari, Gender CC, Water for the Future, and the Alexandra Water Warriors in Johannesburg. Learn more.
More than 140,000 papaya, mango and date palm seedlings have been planted, too, alongside other fruit-bearing trees. These trees enhance soil moisture retention, reduce surface evaporation, and, once mature, allow local farmers to sell the fruit and diversify their income streams. This additional revenue stream is especially important for boosting women’s long-term economic resilience.
The project is also rehabilitating riverbanks: People have planted more than 40,000 trees along the Dechatu to create buffer zones and mitigate flood impacts.
Johannesburg, South Africa Expands Green Space to Prevent Flooding
Johannesburg is a city of approximately 5.6 million people built at the source of the Jukskei river. The city’s waterways have suffered a near complete loss of habitat. As the Jukskei winds through Johannesburg, pollution from solid waste, industrial discharge and sewage have severely degraded the river’s health. For city residents living in vulnerable or informal neighborhoods, the river poses immense health and flood risks.
One of the biggest contributors to the city’s flood risk comes from invasive species. Eucalyptus, introduced to South Africa in the 1800s, crowds the city’s riverbanks and disrupts the flow of water. In some places, other invasive species like saringa, bug weed and mulberry dominate the riverside — affecting local biodiversity by displacing native species. During months of heavy rainfall, thickets of these aggressive species are part of the reason the river overflows: Without space for stormwater to flow, the Jukskei often bursts its banks and floods nearby neighborhoods like Alexandra and Buccleuch.
That’s why the city and local partners are expanding green spaces in Johannesburg’s dense neighborhoods, bringing nature to the built environment. In the overcrowded Alexandra Township, the SUNCASA project has planted 13,000 trees, informed by spatial analysis and local tree audits. In addition to fortifying the landscape, these trees provide much needed shade, cooling the city and mitigating the urban heat island effect. Project organizers also distribute peach and citrus trees to local households which, when cultivated, can create small pockets of green and produce fruit for their families.
Local communities are also clearing the invasive species crowding the city’s riverbanks. By replacing aggressive plants with ecosystem-friendly trees like wild olives and tree wisteria, SUNCASA is helping to control flash floods, restore soil health and increase the capacity of the city’s waterways while improving both water quality and quantity.
The project complements these natural solutions with cleanups of the river’s excessive plastics and other solid waste. Volunteers and artisans work together to repurpose water bottles, papers, tree logs, bricks and plastic bags into art installations.
Employing Nature-based Solutions in Cities
As cities in Africa and elsewhere continue to expand, investments in infrastructure and economic growth must go hand in hand with investments in nature. Planning the future must include not only roads, buildings and industry, but also forests, rivers and other natural infrastructure that sustain life and economic progress.
By prioritizing watershed restoration and conservation, city leaders can ensure that urban growth is water-resilient and creates lasting benefits for people, nature and climate.
