There is increasing global interest in employing nature-based solutions, such as reforestation and wetland restoration, to help reduce water risks to economies and society, including water pollution, floods, droughts and water scarcity, that are likely to become worse under future climates. Africa is exposed to many such water risks. Nature-based solutions for adaptation should be designed to benefit biodiversity and can also provide multiple co-benefits, such as carbon sequestration. A systematic review of over 10 000 publications revealed 150 containing 492 quantitative case studies related to the effectiveness of nature-based solutions for downstream water quantity and water quality (including sediment load) in Africa. The solutions assessed included landscape-scale interventions and patterns (forests and natural wetlands) and site-specific interventions (constructed wetlands and urban interventions e.g. soakaways). Consistent evidence was found that nature-based solutions can improve water quality. In contrast, evidence of their effectiveness for improving downstream water resource quantity was inconsistent, with most case studies showing a decline in water yield where forests (particularly plantations of non-native species) and wetlands are present. The evidence further suggests that restoration of forests and floodplain wetlands can reduce flood risk, and their conservation can prevent future increases in risk; in contrast, this is not the case for headwater wetlands. Potential trade-offs identified include nature-based solutions reducing flood risk and pollution, whilst decreasing downstream water resource quantity. The evidence provides a scientific underpinning for policy and planning for nature-based solutions to water-related risks in Africa, though implementation will require local knowledge.

全球越来越关注采用基于自然的解决方案，例如重新造林和湿地恢复，以帮助减少经济和社会面临的水风险，包括水污染、洪水、干旱和水资源短缺，这些风险在未来气候下可能会变得更糟。非洲面临许多此类水风险。基于自然的适应解决方案应旨在使生物多样性受益，并且还可以提供多种共同利益，例如碳固存。对 10 000 多份出版物的系统审查揭示了 150 份包含 492 个定量案例研究，这些案例研究与非洲下游水量和水质（包括沉积物负荷）基于自然的解决方案的有效性有关。评估的解决方案包括景观尺度的干预措施和模式（森林和自然湿地）和特定地点的干预措施（人工湿地和城市干预措施，例如渗水区）。一致的证据表明，基于自然的解决方案可以改善水质。相比之下，它们对改善下游水资源量的有效性的证据不一致，大多数案例研究表明，在存在森林（特别是非本地物种的种植园）和湿地的地方，水产量下降。证据进一步表明，恢复森林和洪泛区湿地可以降低洪水风险，保护它们可以防止未来风险增加；相比之下，源头湿地则不然。确定的潜在权衡包括基于自然的解决方案，减少洪水风险和污染，同时减少下游水资源量。尽管实施需要当地知识，但证据为非洲与水相关风险的基于自然的解决方案的政策和规划提供了科学依据。