Waterways To Resilience: A Series On Nature-Based Solutions For Water And Climate Challenges In Africa

Victoria Falls (Mosi-oa-Tunya) on the Zambezi River.

The UN Climate Change Conference (COP27) concluded last month in Egypt and the UN Biodiversity Conference (COP15) concluded late last night. There's a thread that connects the commitments and investments that should flow from both: Nature-based Solutions. In a series of blog posts, I'll explore how NbS can contribute to both climate and nature goals, and will ground that exploration in the water, climate, and nature challenges of Africa, drawing on a report that was released at COP27: Waterways to Resilience: Nature-based Solutions for Adaptation in Africa (I was lead author). This post will be an overview of the main message of the report, and a roadmap to the subsequent posts. Nature-based Solutions (NbS) can be defined as 'Actions to protect, sustainably manage, and restore natural or modified ecosystems, that address societal challenges effectively and adaptively, simultaneously providing human well-being and biodiversity benefits.' The societal challenges can encompass both the mitigation of climate change, such as through forests that sequester carbon, and the adaptation to climate change, such as wetlands used to reduce flood risk. This series focuses on NbS primarily in their role for climate adaptation. The definition of, and concepts that underpin, NbS will be explored further in the second post.

The people and economies of Africa confront a range of water-management challenges, including risks from degraded water quality, water scarcity and drought, flooding from both rivers and from stormwater within cities, and coastal erosion and flooding. For much of the continent, these challenges are projected to increase due to climate change over the next several decades - a period in which the continent's population is projected to increase by approximately one billion people. For example, the proportion of Africa's population that lives in areas with a high level of flood risk is projected to increase from 23% today to 54% by 2050 (Figure 1).

Figure 1. The number and proportion of Africa's population living in areas with a risk level for ... [+] flooding of high or greater in 2020 and in 2050 under a climate-change scenario reflecting current trends (a warming of approximate 2degC by the end of the century), from an analysis using WWF's Water Risk Filter.WWF Africa has also seen a rapid decline in the extent of its forests and the health of its wildlife, with populations of monitored wildlife declining by 66% since 1970 and with freshwater-dependent populations showing the most precipitous fall. Because freshwater fisheries are key food resources in much of rural Africa, this degradation and loss of nature also undermines food security. The climate, water and nature challenges confronting Africa will be the focus of the third post.

Addressing these challenges will require a range of solutions, implemented from the scale of small communities to wide regions. There is growing evidence that Nature-based Solutions (NbS) should be included among these solutions and interventions. NbS interventions can contribute to addressing both challenges: adapting to climate change and also reversing the decline of nature.

Typical NbS interventions for adaptation include:

• Forest restoration or protection. Forests with deep soils can promote infiltration of rainfall. This contributes to the recharge of shallow groundwater, reduces runoff and therefore flood flows, and reduces surface erosion, decreasing the amount of sediment and associated nutrients that enter water supplies.

• Wetland restoration or protection. Strategically placed wetlands or ponds can help manage runoff to reduce the volume and rate of water that flows into streams and to filter nutrients and other pollution.

• Floodplain protection or reconnection. Floodplains that remain connected, or are reconnected, and that are allowed to flood can reduce flood risks for cities or farms. Floodplains that become inundated can also promote groundwater recharge, which can be a component of managed aquifer recharge (MAR), or water banking, which can be managed in conjunction with water supply reservoirs. Reconnecting rivers to their floodplains can also reduce nutrient pollution through deposition of sediment and phosphorous and biological processing of nitrates.

• 'Green infrastructure' for stormwater in cities. Cities are dominated by impervious surfaces - including rooftops, parking lots and roads - and thus only a small proportion of rainfall infiltrates into the soil. Compared to an undeveloped watershed, an urban area will produce five times as much surface runoff for the same rainfall event. A range of NbS interventions can be used to increase infiltration, slow down and store runoff, and reduce flood peaks, including vegetated or green roofs, retention ponds, bioswales, and wetlands. These features can be integrated with parks or green spaces and provide a range of other benefits to people in cities, including access to nature, recreation, and local cooling during the summer.

• Mangroves and coastal protection. Mangroves along a coastline can reduce wave energy, attenuate storm surges, lower rates of erosion and maintain shoreline elevation by trapping sediment and promoting deposition.Huayang Lake Wetland Park, Dongguan, Guangdong Province, China. Urban wetlands can reduce stormwater ... [+] flooding in cities, improve water quality and provide citizens with access to green spaces, recreation and the cooling benefits of trees.

We reviewed the evidence that these interventions can effectively address water and climate challenges, drawing on both a global evidence review of NbS from Oxford and the first evidence review of NbS for water challenges for Africa. Both of these reviews found strong evidence that these interventions can make effective contributions to a range of societal challenges. For example, the Africa-specific study found consistent evidence that the presence of floodplains decreased downstream flood risk (Figure 2).

Figure 2. Impact of existing floodplains in Africa on flood levels downstream (adapted from Acreman ... [+] et al.

The evidence for the effectiveness of NbS interventions is reviewed in the fourth post, while the fifth post will go deep on a specific type of Nature-based Solutions: rivers that deliver sediment to build up and maintain downstream deltas and mangrove forests that can provide buffers to coastal storms, floods and erosion.

It is clear that that NbS have considerable potential to contribute to managing water challenges in Africa. However, funding and implementation of NbS programs and projects lags far behind, both in Africa and globally. Although there is evidence that funding for NbS is growing, the UN Environment Program's Adaptation Gap Report 2020 concludes that adaptation funds are not keeping up with needed investment in adaptation:

'Funding for NbS makes up only a tiny fraction of total adaptation and conservation finance, despite many commitments by governments, the private sector, philanthropy and finance institutions for scaling up ambition and investments in NbS.'

A range of institutional and economic barriers constrain broader uptake of NbS. The sixth post reviews these constraints and offers a range of recommendations for overcoming them and scaling up NbS. Because NbS are implemented in complicated socio-cultural settings, the seventh post reviews a set of caveats and best practices around NbS.

The news is filled with reports of prolonged droughts and extreme floods and scientists are increasingly able to find the fingerprints of climate change on these events. Meanwhile, a consistent flow of scientific papers and reports develop a strong case that, without rapid action on reducing emissions, these challenges will only get worse.

These challenges and risks will be felt by communities, companies and countries. Communities will face increasing risks from extreme floods, including loss of life and property, and disruptions to water and food supplies. Companies will confront these same local risks, along with disruptions to their supply chains, as well as reputational and regulatory risks as communities and countries respond to changing conditions. All of these translate into risks for financial institutions and insurance companies. Finally, national governments will need to address these diverse risks to their people, infrastructure, and economic systems to ensure that their countries remain strong and resilient in the face of climate change.

Collectively, these rising risks - and drumbeat of reports and stories of disaster - make it seem as if the forces of nature are increasingly arrayed against our homes, businesses and economies. But the world can also harness the power of nature to help build resilience and defend us against these risks by investing in Nature-based Solutions. In the following series of post, I will explore how - through widespread implementation of NbS - the countries and people of Africa can get nature on their side in their efforts to manage water challenges.