Water security is important for sustaining livelihoods, human well-being, and socio-economic development. It involves safeguarding sustainable access to adequate quantities of acceptable water as well as protection against water risks. Achieving water security depends on a number of elements including natural processes, infrastructure, institutions, and governance.
Water insecurity is increasing and nature-based solutions (NbS) can address some key water security challenges. Drivers of water insecurity include rising global water demands, population growth, rising agricultural demands to support food security, urbanisation, and climate change. Water availability is becoming more variable and unpredictable as climate change is altering the global water cycle, including increasing the frequency and severity of extreme events including floods and droughts. Water is essential for sustainable development, and in the context of climate change, upscaling NbS will be necessary to achieve sustainable development goals (SDGs) (WWAP/UN-Water, 2018).
NbS protect, sustainably manage, and restore natural and modified ecosystems to address societal challenges (Cohen-Shacham et al., 2016). By improving the location, timing and quality of water, NbS can improve water supply and quality, contribute to disaster risk reduction and provide a number of co-benefits. NbS can support water security in both rural and urban settings and for a range of purposes including agricultural production and water, sanitation, and hygiene (WASH). Situating NbS within wider discussions of water allocations between different users and jurisdictions can also help to mitigate trade-offs and tensions, and potentially increase cooperation as improvements to river health and environmental flows benefit all users. As such, they can strengthen water security more broadly.
NbS is an umbrella term for a range of approaches and activities including source water protection, watershed management, wetlands restoration, protection, and construction, water harvesting, agricultural best management practices, afforestation, sustainable drainage systems, and protecting mangroves, amongst others. Many of these approaches and activities, such as integrated water resources management, afforestation, and sustainable drainage systems, which are well-documented, are not new. However, the term NbS is relatively new, particularly with regards to being commonly used by practitioners and policy-makers.
Co-benefits that can be derived from NbS include improvements in human health, biodiversity, livelihoods and climate change mitigation and adaptation. For example, land conservation and water harvesting in Rajasthan, India has increased water security, increased productive farmland with gains for livelihoods, facilitated the return of wildlife and improved the position of women. In Peru, mainstreaming source water protection is addressing both climate and water security risks. To maximise co-benefits, they should be included in the design stage of an intervention.
NbS can also support strengthening water security for future pandemic preparedness and ‘building back better’ in light of Covid-19. Water insecurity, including poor WASH services, can hamper measures to combat and suppress pandemics such as handwashing and social distancing. Linking NbS, social protection and public works programmes could support economic recovery following Covid-19. For example, Pakistan’s recovery efforts include the creation of over 63,000 jobs planting trees as part of a pre-existing programme to combat climate change. In India, the UTFI (underground taming of floods for irrigation) project, which facilitates aquifer recharge, is registered with the Mahatma Gandhi Rural Employment Scheme allowing communities to be remunerated for participating (WWAP/UN-Water, 2018).
NbS are increasing in prominence on the policy agenda and in the investment decisions of a range of stakeholders. Reasons for this include: the need for water infrastructure investment is outpacing financial flows to the sector; climate change is challenging the resilience of grey infrastructure; and, the increasing need to find multi-purpose solutions that can address more than one problem. Investment in NbS by governments, water utilities and companies to support clean, reliable water supplies for cities and communities has increased from USD 8.2 billion in 2011 to USD 24.6 billion in 2015 (Bennett & Ruef, 2016; Bennett & Caroll, 2014). However, between 2013 and 2015, global private finance invested USD 3 billion in water infrastructure, predominately in grey infrastructure.
Grey infrastructure solutions for water security still dominate the policy agenda. The Asian Development Bank (2019b) argues that clear and constant dialogue is needed to build understanding, capacity and drive uptake of NbS by addressing government and private sector perceptions around expense, difficulty and time frames. Sharing pilot projects and data as ‘proof of concept’ can boost government confidence (ABD, 2019b). This could also help to overcome the skew in the evidence base towards developed country applications of NbS.
Examples of best practice
The breadth of NbS and the evidence base means that it is not possible to consider all types of NbS for water security adequately in one report, consequently, this report highlights the following:
- Water for agriculture: sustainable water for agriculture is vital due to rising food demands and the sector’s dominance of water use (70% of all water withdrawals are for agriculture). NbS can improve water supply for rain-fed agricultural systems and support increases in crop production. Activities focus on soil and water conservation and include conservation agriculture, manuring/composting, vegetative strips/covers, agroforestry
and water harvesting. Solutions such as sand dams can also, in some contexts, provide supplementary water for irrigation by facilitating groundwater infiltration. Managing diffuse run-off of excess nutrients from agriculture is the most prevalent water quality challenge globally. NbS can improve water quality by reducing nutrient and sediment run-off from agricultural land into water bodies through approached such as riparian grass and tree buffers, and vegetative waterways.
- Source water protection and water funds: healthy source watersheds collect, filter and store water and are important for urban water supply. Source water protection can reduce water treatment costs for cities, contribute to improved access to drinking water for rural communities, improve water quality for hydropower production and support resilience. Water funds are institutional platforms bringing together different water users to collectively invest in upstream habitat protection and land management, and mobilise innovative sources of funding (Abell et al., 2017). The Upper Tana-Nairobi Water Fund estimates that a USD 10 million investment in watershed conservation activities could lead to a return of USD 21.5 million including savings from wastewater treatment, increased power generation and increased agricultural yields.
- Urban green infrastructure: China’s ‘Sponge cities’ utilise a number of green infrastructure approaches such as green roofs, pervious pavements, rain gardens and restoration of peri-urban wetlands to manage stormwater run-off, retaining some water for re-use. By 2030, the goal is for 80% of urban areas to use these methods to intercept, absorb and reuse 70% of rainwater. Other examples of urban green infrastructure include constructed wetlands for wastewater treatment and disaster risk reduction.