UN WATER
The United Nations World Water Development Report 2018
Executive Summary
Nature-based solutions (NBS) are inspired and supported by nature and use, or mimic, natural processes to contribute to the improved management of water. An NBS can involve conserving or rehabilitating natural ecosystems and/or the enhancement or creation of natural processes in modified or artificial ecosystems. They can be applied at micro- (e.g. a dry toilet) or macro(e.g. landscape) scales.
Attention to NBS has significantly increased in recent years. This is evidenced through the mainstreaming of NBS into a wide range of policy advances, including in water resources, food security and agriculture, biodiversity, environment, disaster risk reduction, urban settlements, and climate change. This welcome trend illustrates a growing convergence of interests around the recognition of the need for common objectives and the identification of mutually supporting actions – as illustrated best in the 2030 Agenda for Sustainable Development through its acknowledgment of the interdependency of its various Goals and targets.
Upscaling NBS will be central to achieving the 2030 Agenda for Sustainable Development. Sustainable water security will not be achieved through business-as-usual approaches. NBS work with nature instead of against it, and thereby provide an essential means to move beyond business-as-usual to escalate social, economic and hydrological efficiency gains in water resources management. NBS show particular promise in achieving progress towards sustainable food production, improved human settlements, access to water supply and sanitation services, and water-related disaster risk reduction. They can also help to respond to the impacts of climate change on water resources.
NBS support a circular economy that is restorative and regenerative by design and promotes greater resource productivity aiming to reduce waste and avoid pollution, including through reuse and recycling. NBS also support the concepts of green growth or the green economy, which promote sustainable natural resource use and harness natural processes to underpin economies. The application of NBS for water also generates social, economic and environmental co-benefits, including improved human health and livelihoods, sustainable economic growth, decent jobs, ecosystem rehabilitation and maintenance, and the protection and enhancement of biodiversity. The value of some of these co-benefits can be substantial and tip investment decisions in favour of NBS.
However, despite a long history of and growing experience with, the application of NBS, there are still many cases where water resources policy and management ignore NBS options – even where they are obvious and proven to be efficient. For example, despite rapidly growing investments in NBS, the evidence suggests that this is still well below 1% of total investment in water resources management infrastructure.
The world’s water: Demand, availability, quality and extreme events
The global demand for water has been increasing at a rate of about 1% per year as a function of population growth, economic development and changing consumption patterns, among other factors, and it will continue to grow significantly over the next two decades. Industrial and domestic demand for water will increase much faster than agricultural demand, although agriculture will remain the largest overall user. The vast majority of the growing demand for water will occur in countries with developing or emerging economies.
At the same time, the global water cycle is intensifying due to climate change, with wetter regions generally becoming wetter and drier regions becoming even drier. At present, an estimated 3.6 billion people (nearly half the global population) live in areas that are potentially water-scarce at least one month per year, and this population could increase to some 4.8–5.7 billion by 2050.
Since the 1990s, water pollution has worsened in almost all rivers in Africa, Asia and Latin America. The deterioration of water quality is expected to further escalate over the next decades and this will increase threats to human health, the environment and sustainable development. Globally, the most prevalent water quality challenge is nutrient loading, which, depending on the region, is often associated with pathogen loading. Hundreds of chemicals are also impacting on water quality. The greatest increases in exposure to pollutants are expected to occur in low-and lower-middle income countries, primarily because of higher population and economic growth and the lack of wastewater management systems.
The trends in water availability and quality are accompanied by projected changes in flood and drought risks. The number of people at risk from floods is projected to rise from 1.2 billion today to around 1.6 billion in 2050 (nearly 20% of the world’s population). The population currently affected by land degradation/desertification and drought is estimated at 1.8 billion people, making this the most significant category of ‘natural disaster’ based on mortality and socio-economic impact relative to gross domestic product (GDP) per capita.
Ecosystem degradation
Ecosystem degradation is a leading cause of increasing water resources management challenges. Although about 30% of the global land remains forested, at least two thirds of this area are in a degraded state. The majority of the world’s soil resources, notably on farmland, are in only fair, poor or very poor condition and the current outlook is for this situation to worsen, with serious negative impacts on water cycling through higher evaporation rates, lower soil water storage and increased surface runoff accompanied by increased erosion. Since the year 1900, an estimated 64–71% of the natural wetland area worldwide has been lost due to human activity. All these changes have had major negative impacts on hydrology, from local to regional and global scales.
There is evidence that such ecosystem change has over the course of history contributed to the demise of several ancient civilizations. A pertinent question nowadays is whether we can avoid the same fate. The answer to that question will depend at least partly on our ability to shift from working against nature to working with it – through, for example, better adoption of NBS.
The role of ecosystems in the water cycle
Ecological processes in a landscape influence the quality of water and the way it moves through a system, as well as soil formation, erosion, and sediment transport and deposition – all of which can exert major influences on hydrology. Although forests often receive the most attention when it comes to land cover and hydrology, grasslands and croplands also play important roles. Soils are critical in controlling the movement, storage and transformation of water. Biodiversity has a functional role in NBS whereby it underpins ecosystem processes and functions and, therefore, the delivery of ecosystem services.
Ecosystems have important influences on precipitation recycling from local to continental scales. Rather than being regarded as a ‘consumer’ of water, vegetation is perhaps more appropriately viewed as a water ‘recycler’. Globally, up to 40% of terrestrial rainfall originates from upwind plant transpiration and other land evaporation, with this source accounting for most of the rainfall in some regions. Land use decisions in one place may therefore have significant consequences for water resources, people, the economy and the environment in distant locations – pointing to the limitations of the watershed (as opposed to the ‘precipitationshed’) as the basis for management.
Green infrastructure (for water) uses natural or seminatural systems such as NBS to provide water resources management options with benefits that are equivalent or similar to conventional grey (built/physical) water infrastructure. In some situations, nature-based approaches can offer the main or only viable solution (for example, landscape restoration to combat land degradation and desertification), whereas for different purposes only a grey solution will work (for example supplying water to a household through pipes and taps). In most cases, however, green and grey infrastructure can and should work together. Some of the best examples of the deployment of NBS are where they improve the performance of grey infrastructure. The current situation, with ageing, inappropriate or insufficient grey infrastructure worldwide, creates opportunities for NBS as innovative solutions that embed perspectives of ecosystem services, enhanced resilience and livelihood considerations in water planning and management.
A key feature of NBS is that they tend to deliver groups of ecosystem services together – even if only one is being targeted by the intervention. Hence, NBS usually offer multiple water-related benefits and often help address water quantity, quality and risks simultaneously. Another key advantage of NBS is the way in which they contribute to building overall system resilience.
NBS for managing water availability
NBS mainly address water supply through managing precipitation, humidity, and water storage, infiltration and transmission, so that improvements are made in the location, timing and quantity of water available for human needs.
The option of building more reservoirs is increasingly limited by silting, decrease of available runoff, environmental concerns and restrictions, and the fact that in many developed countries the most cost-effective and viable sites have already been used. In many cases, more ecosystem-friendly forms of water storage, such as natural wetlands, improvements in soil moisture and more efficient recharge of groundwater, could be more sustainable and cost-effective than traditional grey infrastructure such as dams.
Agriculture will need to meet projected increases in food demand by improving its resource use efficiency while simultaneously reducing its external footprint, and water is central to this need. A cornerstone of recognized solutions is the ‘sustainable ecological intensification’ of food production, which enhances ecosystem services in agricultural landscapes, for example through improved soil and vegetation management. ‘Conservation agriculture’, which incorporates practices aimed at minimizing soil disturbance, maintaining soil cover and regularizing crop rotation, is a flagship example approach to sustainable production intensification. Agricultural systems that rehabilitate or conserve ecosystem services can be as productive as intensive, high-input systems, but with significantly reduced externalities. Although NBS offer significant gains in irrigation, the main opportunities to increase productivity are in rainfed systems that account for the bulk of current production and family farming (and hence provide the greatest livelihood and poverty reduction benefits). The theoretical gains that could be achievable at a global scale exceed the projected increases in global demand for water, thereby potentially reducing conflicts among competing uses.
NBS for addressing water availability in urban settlements are also of great importance, given that the majority of the world’s population is now living in cities. Urban green infrastructure, including green buildings, is an emerging phenomenon that is establishing new benchmarks and technical standards that embrace many NBS. Business and industry are also increasingly promoting NBS to improve water security for their operations, prompted by a compelling business case.
NBS for managing water quality
Source water protection reduces water treatment costs for urban suppliers, and contributes to improved access to safe drinking water in rural communities. Forests, wetlands and grasslands, as well as soils and crops, when managed properly, play important roles in regulating water quality by reducing sediment loadings, capturing and retaining pollutants, and recycling nutrients. Where water becomes polluted, both constructed and natural ecosystems can help improve water quality.
Non-point (diffuse) source pollution from agriculture, notably nutrients, remains a critical problem worldwide, including in developed countries. It is also the one most amenable to NBS, as these can rehabilitate ecosystem services that enable soils to improve nutrient management, and hence lower fertilizer demand and reduce nutrient runoff and/or infiltration to groundwater.
Urban green infrastructure is increasingly being used to manage and reduce pollution from urban runoff. Examples include green walls, roof gardens and vegetated infiltration or drainage basins to support wastewater treatment and reduce stormwater runoff. Wetlands are also used within urban environments to mitigate the impact of polluted stormwater runoff and wastewater. Both natural and constructed wetlands also biodegrade or immobilize a range of emerging pollutants, including certain pharmaceuticals, and often perform better than grey solutions. For certain chemicals, they may offer the only solution.
There are limits to how NBS can perform. For example, NBS options for industrial wastewater treatment depend on the pollutant type and its loading. For many polluted water sources, grey-infrastructure solutions may continue to be needed. However, industrial applications of NBS, particularly constructed wetlands for industrial wastewater treatment, are growing
NBS for managing water-related risks
Water-related risks and disasters, such as floods and droughts associated with an increasing temporal variability of water resources due to climate change, result in immense and growing human and economic losses globally. Around 30% of the global population is estimated to reside in areas and regions routinely impacted by either flood or drought events. Ecosystem degradation is the major cause of increasing water-related risks and extremes, and it reduces the ability to fully realize the potential of NBS.
Green infrastructure can perform significant risk reduction functions. Combining green and grey infrastructure approaches can lead to cost savings and greatly improved overall risk reduction.
NBS for flood management can involve water retention by managing infiltration and overland flow, and thereby the hydrological connectivity between system components and the conveyance of water through it, making space for water storage through, for example, floodplains. The concept of ‘living with floods’, which, among other things, includes a range of structural and non-structural approaches that help to ‘be prepared’ for a flood, can facilitate the application of relevant NBS to reduce flood losses and, most importantly, flood risk.
Droughts are not limited to dry areas, as is sometimes portrayed, but can also pose a disaster risk in regions that are normally not water-scarce. The mix of potential NBS for drought mitigation is essentially the same as those for water availability and aim to improve water storage capacity in landscapes, including soils and groundwater, to cushion against periods of extreme scarcity. Seasonal variability in rainfall creates opportunities for water storage in landscapes to provide water for both ecosystems and people over drier periods. The potential of natural water storage (particularly subsurface, in aquifers) for disaster risk reduction is far from being realized. Storage planning at river basin and regional scales should consider a portfolio of surface and subsurface storage options (and their combinations) to arrive at the best environmental and economic outcomes in the face of increasing water resources variability.
Download full version (PDF): Nature-Based Solutions for Water
About UN Water
www.unwater.org
There is no single UN entity dedicated exclusively to water issues. Over 30 UN organizations carry out water and sanitation programmes, reflecting the fact that water issues run through all of the UN’s main focus areas. UN-Water’s role is to coordinate so that the UN family ‘delivers as one’ in response to water related challenges.
Tags: Nature-Based Solutions for Water, NBS, UN Water, UNESCO, United Nations, Water
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