UN World Water Development Report 2020 - Water and Climate Change

Executive Summary

WATER AND CLIMATE CHANGE

The United Nations World Water Development Report 2020World Water Assessment Programme United Nations Educational, Scientific and Cultural OrganizationSustainable Development Goals water and sanitation United NationsEducational, Scientific andCultural Organization

The United Nations World Water Development Report 2020 .

Climate change will affect the availability, quality and quantity of water for basic human needs, threatening the effective enjoyment of the human rights to water and sanitation for potentially billions of people. The hydrological changes induced by climate change will add challenges to the sustainable management of water resources, which are already under severe pressure in many regions of the world. Food security, human health, urban and rural settlements, energy production, industrial development, economic growth, and ecosystems are all water-dependent and thus vulnerable to the impacts of climate change. Climate change adaptation and mitigation through water management is therefore critical to sustainable development, and essential to achieving the 2030 Agenda for Sustainable Development, the Paris Agreement on Climate Change and the Sendai Framework for Disaster Risk Reduction.Impacts on water resources Global water use has increased by a factor of six over the past 100 years and continues to grow steadily at a rate of about 1% per year as a result of increasing population, economic development and shifting consumption patterns. Combined with a more erratic and uncertain supply, climate change will aggravate the situation of currently water-stressed regions, and generate water stress in regions where water resources are still abundant today. Physical water scarcity is often a seasonal phenomenon, rather than a chronic one, and climate change is likely to cause shifts in seasonal water availability throughout the year in several places.Climate change manifests itself, amongst others, in the increasing frequency and magnitude of extreme events such as heatwaves, unprecedented rainfalls, thunderstorms and storm surge events.Water quality will be adversely affected as a result of higher water temperatures, reduced dissolved oxygen and thus a reduced self-purifying capacity of freshwater bodies.

There are further risks of water pollution and pathogenic contamination caused by flooding or by higher pollutant concentrations during drought.Many ecosystems, particularly forests and wetlands, are also at risk. The degradation of ecosystems will not only lead to biodiversity loss, but also affect the provision of water-related ecosystem services, such as water purification, carbon capture and storage, and natural flood protection, as well as the provision of water for agriculture, fisheries and recreation.Much of the impacts of climate change will be manifested in the tropical zones where most of the developing world can be found. Small island developing states are typically environmentally and socio-economically vulnerable to disasters and climate change, and many will experience increasing water stress.

Across the planet, drylands are expected to expand significantly. Accelerated melting of glaciers is expected to have a negative effect on the water resources of mountain regions and their adjacent lowlands.Despite the growing evidence that the changing climate will affect the availability and distribution of water resources, some uncertainties remain, especially at local and basin scales. While there is not much disagreement about the temperature increases, which have been simulated by different general circulation models (GCMs) under specific scenario conditions, more variability and ambiguity exist in projected precipitation trends. Often, trends in extremes (heavier precipitation, heat, prolonged droughts) show a clearer direction than trends in annual precipitation totals and seasonal patterns.Much of the impacts of climate change will be manifested in the tropical zones where most of the developing world can be found

Adaptation and mitigation

Adaptation and mitigation are complementary strategies for managing and reducing the risks of climate change. Adaptation encompasses a combination of natural, engineered and technological options, as well as social and institutional measures to moderate harm or exploit beneficial opportunities from climate change. Adaptation options exist in all water-related sectors and should be investigated and applied where possible. Mitigation comprises human interventions to reduce the sources or enhance the sinks of greenhouse gases (GHGs). While mitigation options are also available across every major water-related sector, they remain largely unrecognized.International policy frameworksWithin the 2030 Agenda, water serves as an (often) unacknowledged but essential connecting factor for attaining the different Sustainable Development Goals (SDGs). As such, failure to adapt to climate change not only puts the realization of SDG 6 (the ‘water goal’) at risk, it also jeopardizes the achievement of most other SDGs. And while SDG 13 “Take urgent action to combat climate change and its impacts” includes specific targets and indicators, there is no formal mechanism linking SDG 13 to the goals of the Paris Agreement, resulting in parallel processes.Although water is not mentioned in the Paris Agreement per se, it is an essential component of nearly all the mitigation and adaptation strategies. However, water is identified as the number one priority for adaptation actions in most of the intended nationally determined contributions (INDCs) and is directly or indirectly related to all other priority areas. Similarly, water is hardly mentioned in the Sendai Framework itself, even though water flows through each of the priorities for action and is central to all its seven targets.The challenges of development, poverty eradication and sustainability are intricately interwoven with those of climate change mitigation and adaptation, especially through water. Given water’s role in mitigating and adapting to climate change, water could play a connecting role across the SDGs and across policy frameworks such as the Paris Agreement.Water resources management, infrastructure and ecosystemsClimate change generates additional risks to water-related infrastructure, requiring an ever-increasing need for adaptation measures. Water-related extremes exacerbated by climate change increase risks to water, sanitation and hygiene (WASH) infrastructure, such as damaged sanitation systems or flooding of sewer pumping stations. The consequent spread of faeces and associated protozoa and viruses can cause severe health hazards and cross-contamination.For water storage infrastructure, there is a need to reassess the safety and sustainability of dams, and to evaluate them for potential modifications or decommissioning, for the minimization of their environmental and social impacts, and for the optimization of their services.The challenges of development, poverty eradication and sustainability are intricately interwoven with those of climate change mitigation and adaptation, especially through water.

In many regions of the world, aquifers present the largest storage capacity, often orders of magnitude greater than surface water storage. Groundwater is also more buffered from seasonal and multi-year climate variability and less immediately vulnerable than surface water.It is increasingly necessary to consider ‘unconventional’ water resources in future planning. Water reuse (or reclaimed water) is a reliable alternative to conventional water resources for a number of uses, provided that it is treated and/or used safely. Desalination can augment freshwater supplies, but it is generally energy-intensive and thus may contribute to GHG emissions if the power source is non-renewable. Atmospheric moisture harvesting such as cloud seeding, or fog water collection presents a low-cost and low-maintenance approach for localized areas where advective fog is abundant.The bulk of the GHG emissions related to water management and sanitation either originates from the energy used to power the systems or the biochemical processes involved in water and wastewater treatment. Increasing water use efficiency and reducing unnecessary water consumption and water loss both translate into lower energy use and thus lower GHG emissions.Wetlands accommodate the largest carbon stocks among terrestrial ecosystems, storing twice as much carbon as forests. Taking into account that wetlands offer multiple co-benefits – including flood and drought mitigation, water purification, and biodiversity – their restoration and conservation is of critical importance.Disaster risk reductionThe current impacts and future anticipated risks associated with extreme events demand sustainable solutions for climate change adaptation and disaster risk reduction.The range of available climate change adaptation and disaster risk reduction strategies includes hard (structural) and soft (policy instruments) approaches. Hard measures include enhanced water storage, climate-proof infrastructure, and crop resilience improvements through the introduction of flood- and drought-resistant crop varieties. Soft measures include flood and drought insurance, forecasting and early warning systems, land use planning, and capacity building (education and awareness). Hard and soft measures often go together. Urban planning, for example, can help increase resilience to flood risks by featuring drainage systems that provide spaces to safely collect and store floodwater. The city thus acts as a ‘sponge’, limiting surges and releasing rainwater as a resource.Modern communication methods such as social media and mobile phone services provide significant opportunities to help improve communication and early warning effectiveness. Drought and flood monitoring systems are also an important component of risk reduction.Mainstreaming gender and community involvement in decision-making processes are key elements to disaster risk reduction strategies. Improved inter-agency coordination in water resources and disaster risk management is needed, especially in transboundary basins where it remains fragmented throughout most of the world.Water reuse(or reclaimed water)is a reliable alternative to conventional water resources for a number of uses, provided that it is treated and/or used safely

Human health

Anticipated water-related health impacts of climate change are primarily food-, water- and vector-borne diseases, deaths and injury associated with extreme weather events such as coastal and inland flooding, as well as undernutrition as a result or food shortages caused by droughts and floods. Mental health impacts associated with illness, injury, economic losses and displacement may also be substantial, although difficult to quantify.At the end of the Millennium Development Goals period (2000–2015), 91% of the global population used an improved drinking water source and 68% used improved sanitation facilities. Much remains to be done to reach the new, higher levels of safely managed water supply and sanitation services as defined under the SDGs for the 2.2 billion and 4.2 billion people respectively who lack this superior level of service.Climate change is likely to slow or undermine progress on access to safely managed water and sanitation, and lead to ineffective use of resources if systems design and management are not climate-resilient. By extension, progress on the elimination and control of water- and sanitation-related disease will also be slowed or undermined by climate change.Food and agricultureThe specific challenges for agricultural water management are twofold. The first is the need to adapt existing modes of production to deal with higher incidences of water scarcity and water excess (flood protection and drainage). The second is to ‘decarbonize’ agriculture through climate mitigation measures that reduce GHG emissions and enhance water availability.The scope for adaptation in rainfed agriculture is determined largely by the ability of crop varieties to cope with shifts in temperature and to manage soil water deficits. Irrigation allows cropping calendars to be rescheduled and intensified, thus providing a key adaptation mechanism for land that previously relied solely on precipitation.In terms of equivalent tonnes of CO2, the largest contribution to agricultural GHG emissions is made by the release of livestock methane through enteric fermentation and manure deposited on pasture. For forestry, the greatest opportunity for mitigation involves reducing the emissions attributable to deforestation and forest degradation.Agriculture has two main avenues for mitigation of GHGs: carbon sequestration through organic matter accumulation above and below the ground, and emission reduction through land and water management, including adoption of renewable energy inputs such as solar pumping. Climate-Smart Agriculture (CSA) is a recognized suite of well-informed approaches to land and water management, soil conservation and agronomic practice that sequester carbon and reduce greenhouse gas emissions. CSA practices help to retain soil structure, organic matter and moisture under drier conditions, and include agronomic techniques (including irrigation and drainage) to adjust or extend cropping calendars to adapt to seasonal and interannual climate shifts.Climate change is likely to slow or undermine progress on access to safely managed water and sanitation

Energy and industryThe water-related effects of climate change generate risks to business and power generation. Water stress can put a halt to manufacturing or energy generation. Impacts will also carry into operational aspects, affecting the supply of raw materials, disrupting supply chains, and causing damage to facilities and equipment.Energy is in the spotlight of climate change initiatives as about two-thirds of the world’s anthropogenic GHGs come from energy production and use. There are a number of opportunities to mitigate GHGs and reduce water use at the same time. Reducing energy demand and increasing energy efficiency are starting points. One promising direction is the increased use of low-carbon renewable energy technology with little water requirements, such as solar photovoltaic (PV) and wind, the costs of which are becoming increasingly competitive with fossil fuel energy generation. While hydropower will continue playing a role in climate mitigation and adaptation of the energy sector, the overall sustainability of single projects needs to be assessed, taking account of potential water consumption through evaporation as well as GHG emissions from reservoirs, not to mention the potential ecological and socio-economic impacts. For business, water stress is one of the main drivers for water reuse and efficiency. In concert with technology, a facility could look at day-to-day operations such as the use of washwater, and better monitoring and leak detection. On an expanded scale, a company might evaluate its water footprint and include those of its suppliers, which may have far-reaching effects if they are large water users.Human settlementsThe impacts of climate change on urban water systems include higher temperatures, reduced precipitation and more severe drought on the one hand, and increasing heavy precipitation and flooding events on the other. It is precisely these extremes that make the planning of urban space and the provision of infrastructure so difficult.The physical infrastructure for delivery of water and sanitation facilities can also be disrupted, leading to contaminated water supplies and the discharge of untreated wastewater and stormwater into living environments. Vectorborne diseases such as malaria, rift valley fever, leptospirosis and others are often observed after flooding events.Urban water resilience goes way beyond the traditional city boundaries. In cases where water supplies rely on distant watersheds, planning needs to look well beyond the city’s boundaries and consider the long-term impacts of urban expansion on distant freshwater ecosystems and the local communities that also rely on them.In small urban and rural settlements, use of water for agriculture and in some cases industrial applications results in reduced availability for domestic uses. Domestic supplies must be prioritized under the human rights to water and sanitation.The water-related effects of climate change generate risks to business and power generation.

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