水与气候变化的关系，你了解吗？

水资源是气候变化解决方案的重要组成部分

 (English version below)

2020年3月22日发布的联合国《世界水发展报告》警示，气候变化将影响满足人类基本需求所需的水的供给、质量和体量，从而损害数十亿人享有安全饮用水和卫生设施的基本权利。报告呼吁各国为应对这一挑战做出更具体的承诺。

情况的恶化会阻碍可持续发展目标6的实现。这一目标是《2030年可持续发展议程》的一部分，它要求在十年内确保所有人获得安全饮用水和卫生设施。这将是一个巨大挑战——目前全球仍有22亿人无法获得安全的饮用水，42亿人（占世界人口的55%）没有合乎要求的卫生设施。

一个世纪以来，人类的用水量增加了6倍，并仍在以每年1%的速度增长。然而据估计，气候变化以及风暴、洪水和干旱等极端事件的频率和强度日益增加将使目前已经面临“水资源紧张”的国家的处境更加恶化，并将目前尚未受到严重影响的地区置于类似境地。此外，报告还指出，水管理不善往往会加剧气候变化对水资源和整个社会的影响。

联合国教科文组织总干事阿祖莱强调：“水带来了一些问题，但也能提供解决方案。水可以为减缓和适应气候变化的努力提供支持。”

联合国水机制主席、国际农业发展基金会主席洪博说:“如果我们想要将全球气温上升幅度限制在2摄氏度以下，并在2030年实现可持续发展目标，那么我们必须立即采取行动。以更加协调的方式管理水和气候是可以做到的，这需要社会各界共同参与。留给我们的时间不多了。”

气候变化影响健康，威胁生物多样性

水温升高和溶解氧减少将影响水质，导致淡水流域水体的自净能力下降。洪水或干旱期间污染物的聚集将增加水污染和病原体污染的风险。除了粮食生产之外，人类身心健康也可能受到相当大的影响，原因有疾病、伤害、经济损失和人民流离失所等。

多种生态系统——特别是森林和湿地——也面临生物多样性减少的威胁。不仅是农业（占淡水使用量的69%），还有工业、能源生产甚至渔业的水供给都将受到影响。

风险最高的地区：群岛、山区、热带和极北

气候变化对水资源的大部分影响将在热带地区凸显，大多数发展中国家位于这一地区，小岛屿国家甚至可能遭受毁灭性的打击，其中一些可能会从地图上消失。由于山地冰川和雪盖的存在，山区也特别容易受到影响，而世界上几乎所有地方的山地冰川和雪盖都呈现消退趋势。然而报告亦提及，由于地方一级降雨模式的季节性变化等原因，一些不确定性仍然存在。

解决方案建议：适应与减缓

面对这些威胁，报告指出了2项应当实施的相辅相成的战略——适应和缓解：

• 适应包括一系列自然、技术和科技选择的组合，以及社会和体制措施，以减轻气候变化带来的损害和利用气候变化的有限积极影响。这一战略可能收效迅速，尤其在地方一级。

• 缓解包括采取行动减少温室气体排放，同时利用碳汇减少大气中二氧化碳和其他温室气体的含量。这一战略可以覆盖较广的地理区域，但可能需要数十年时间方能取得成效。然而，在水资源管理中应用这一战略的可能性在很大程度上仍然没有得到承认。

改善废水处理

废水处理同样加剧气候变化，因为它产生温室气体。据估计，其排放量占温室气体排放总量的3-7%。这些排放来自废水处理的能源消耗和生化工序。但是由于其中含有的有机物质的分解，未经处理的废水也是甲烷——一种典型的温室气体——的主要来源。该报告指出，废水所含的能量超过了对其进行处理所需的能量。当然，前提是人类能够对其中含有的能量加以利用。据估计，全世界80-90%的废水未经任何形式的处理便被排放到环境中去。

具体而言，实现水资源的最优管理意味着投资现代加工技术，以便从有机物中提取甲烷，然后利用这种生物气体提供废水处理过程所需的能源。约旦、墨西哥、秘鲁和泰国等缺水国家已将其付诸实践。这些技术使相关公用设施能够减少数千吨二氧化碳的排放，同时节省资金和提高服务质量。

报告还提到了收集雾水等创新的水资源管理措施，或者湿地保护等更传统的措施，以及已被证实有效的“保护性耕作”技术。这些措施使得在降雨量较少的情况下保护土壤结构、有机物和水分成为可能。同样，只将废水做部分处理以便“再利用”于农业和工业，而不必使其达到饮用安全标准，是另一个值得考虑的方法。

将水列入优先事项

令人担忧的是，报告指出，虽然人们普遍认识到通过改善水循环管理来应对气候变化的重要性，但这一认识并没有转化为现实。“‘水’这个字很少出现在国际气候协定中。”阿祖莱评论道。各国在《巴黎协定》下提交的”国家自主贡献”仍然是一般性的，没有提出具体的水管理计划。虽然大多数国家在其“一揽子行动”中承认水的重要性，但很少有国家实际计算了这些行动的成本，提出具体项目的国家更少。同时，适应和缓解措施之间协同增效的可能性也常常被忽视。

获取气候资金

显然，融资问题至关重要。报告指出，水资源管理以及供水和卫生设施缺乏资金，需要各国予以更多关注。他们认为，目前有越来越多的机会将适应和缓解计划系统性地纳入与水有关的投资，以使得这些投资对捐助者们更具吸引力。

斯里兰卡的“绿色气候基金”项目是一个良好的案例。该方案旨在改善脆弱农村社区的灌溉系统，并在3个河流流域推广气候智能型农业做法，既能将气候变化适应与减缓相结合，又能保护水和饮用水源。

各种水和气候变化倡议还可以产生连带效益，如创造就业机会、改善公共卫生、减少贫困、促进性别平等和改善生计等，这提高了它们对捐助者的吸引力。

报告的作者们总结道，采取综合的适应和缓解措施是一个双赢的做法。显然，它们有利于水资源的可持续管理，有利于保障享有安全饮用水和卫生设施的人权。它们还直接作用于气候变化的原因和后果，包括对极端天气事件的响应。最后，它们有助于许多项可持续发展目标的实现。

联合国《世界水发展报告》是联合国水机制关于水和卫生问题的旗舰报告，每年关注一个不同的主题。该报告由教科文组织代表联合国水机制发表，其编制工作由教科文组织世界水评估计划负责协调。该报告在世界水日当天发布，为决策者提供制定和实施可持续水政策的知识和工具。

教科文组织媒体联系人：

Bernard Giansetto

b.giansetto@unesco.org

+33 (0)1 45 68 17 64

联合国水机制：

Daniella Bostrom Couffe

daniella.bostrom@unwater.org

+41 79 159 92 17

Water resources an essential part of the solution to climate change

Climate change will affect the availability, quality and quantity of water needed for basic human needs, thus undermining enjoyment of the basic rights to safe drinking water and sanitation for billions of people, warns the latest UN World Water Development Report. The authors call on States to make more concrete commitments to address the challenge.

Such a deterioration of the situation would only hinder achievement of Sustainable Development Goal 6 which is part of the 2030 Agenda for Sustainable Development, according to which access to safe drinking water and sanitation must be guaranteed for all within ten years. This will be a considerable challenge – 2.2 billion people currently do not have access to safely managed drinking water, and 4.2 billion, or 55% of the world's population, are without safely managed sanitation.

Water use has increased sixfold over the past century and is rising by about 1% a year. However, it is estimated that climate change, along with the increasing frequency and intensity of extreme events – storms, floods and droughts, will aggravate the situation in countries already currently experiencing ‘water stress’ and generate similar problems in areas that have not been severely affected. Furthermore, the report highlights the fact that poor water management tends to exacerbate the impacts of climate change, not only on water resources but on society as a whole. 

The Director-General of UNESCO, Audrey Azoulay, stresses “that water does not need to be a problem – it can be part of the solution. Water can support efforts to both mitigate and adapt to climate change.”

The Chair of UN-Water, and President of the International Fund for Agricultural Development (IFAD), Gilbert F. Houngbo, says : “If we are serious about limiting global temperature increases to below 2°C and achieving the Sustainable Development Goals by 2030, we must act immediately. There are solutions for managing water and climate in a more coordinated manner and every sector of society has a role to play. We simply cannot afford to wait.”

Health effects, threat to biodiversity

Indeed, water quality will be affected by increased water temperatures and a decrease in dissolved oxygen, leading to a reduction in the self-purification capacity of freshwater basins. We will see increased risks of water pollution and pathogen contamination caused by floods or higher concentrations of pollutants during periods of drought. In addition to the impact on food production, the effects on physical and mental health – linked to disease, injury, financial loss and the displacement of people – are therefore likely to be considerable.

Many ecosystems, particularly forests and wetlands, are also under threat, reducing biodiversity. Water supplies will be affected, not only for agriculture – which accounts for 69% of freshwater withdrawals – but also for industry, energy production and even fisheries.

Areas most at risk: archipelagos, mountains, tropics and Far North

Much of the impact of climate change on water resources will be manifested in the tropics, where most developing countries are located, with potentially apocalyptic consequences for small island states, some of which could be wiped off the map. Mountainous areas are also exceptionally vulnerable through impacts on mountain glaciers and snowcaps, which show a decreasing trend almost everywhere in the world. The authors recognize, however, that a number of uncertainties remain, particularly at the local level and due to the seasonal variability of rainfall patterns.

Suggested solutions: adaptation and mitigation

In the face of these threats, the report highlights the two complementary strategies to be implemented – adaptation and mitigation: 

• Adaptation encompasses a combination of natural, technical and technological options, as well as social and institutional measures to mitigate damage and exploit the few positive consequences of climate change. It is likely to have very rapid benefits, mainly at the local level.

• Mitigation consists of the human actions needed to reduce greenhouse gases (GHGs) emissions while exploiting carbon sinks to reduce the amount of CO2 and other GHGs in the atmosphere. It can involve large geographical areas, but with gains that may spread over decades. However, the possibilities for mitigation in water management remain largely unrecognized.

Improved wastewater management

Wastewater treatment also contributes to climate change as it generates GHGs, accounting for an estimated 3% to 7% of all emissions. These emissions arise from both the energy required for wastewater treatment and the biochemical processes used. But because of the decomposition of the organic matter it contains, untreated wastewater is also a major source of methane, a powerful greenhouse gas. The report points out that wastewater harbours more energy than is needed for its treatment, provided, of course, that it is harnessed. It is estimated that worldwide, between 80% and 90% of wastewater is discharged to the environment without any form of treatment. 

In concrete terms, the optimal management of water resources means investing in modern treatment techniques that allow for the extraction of methane from organic matter and then use this biogas to generate the energy needed to run the process, as is already done in water-scarce countries such as Jordan, Mexico, Peru and Thailand. These techniques have enabled the public utilities concerned to reduce emissions by thousands of tonnes of CO2, while making financial savings and improving the quality of the service.

The report also mentions innovative water management interventions such as fog capture, or more traditional ones such as wetland protection, as well as proven ‘conservation agriculture’ techniques. These make it possible to preserve soil structure, organic matter and moisture, despite lower rainfall. Similarly, the ‘reuse’ of partially treated wastewater for agriculture and industry, without necessarily making it safe to drink, is another interesting approach.

Prioritizing water

Unfortunately, note the authors, while the need to combat climate change through better management of the water cycle is well recognized, it is not being translated into reality. “The word 'water' rarely appears in international climate agreements,” observes Audrey Azoulay. The ‘nationally determined contributions’ submitted by States under the Paris Agreement remain general in nature, without proposing specific plans for water. While a majority of countries recognize water in their 'portfolio of actions', few of them have actually calculated the costs of these actions and even fewer have put forward specific projects. Meanwhile, the possibilities for synergies between adaptation and mitigation measures are often neglected.

Accessing climate funds

The question of finance is obviously crucial. The authors point out that water resources management and water supply and sanitation services are underfunded and require greater attention from States. They argue that there are increasing opportunities to systematically integrate adaptation and mitigation planning into water-related investments, in order to make them more attractive to donors. 

A good example of this is a Green Climate Fund project in Sri Lanka. This aims to improve irrigation systems in vulnerable village communities and promote climate-smart agricultural practices in three river basins, offering both climate adaptation and mitigation benefits, while conserving water and protecting drinking water sources.

Various water and climate change initiatives can also bring co-benefits such as job creation, improved public health, poverty reduction, promotion of gender equality and improved livelihoods, further enhancing their attractiveness to donors.

The adoption of integrated adaptation and mitigation measures is a win-win proposition, conclude the authors of the report. They are clearly beneficial for the sustainable management of water resources and for the human right to safe drinking water and sanitation. They also directly address the causes and consequences of climate change, including in terms of the response to extreme weather events. Finally, they contribute to the achievement of several of the Sustainable Development Goals.

The United Nations World Water Development Report is UN-Water’s flagship report on water and sanitation issues, focusing on a different theme each year. The report is published by UNESCO, on behalf of UN-Water and its production is coordinated by the UNESCO World Water Assessment Programme. Launched in conjunction with World Water Day, the report provides decision-makers with knowledge and tools to formulate and implement sustainable water policies.

Media contact for UNESCO: 

Bernard Giansetto

b.giansetto@unesco.org

+33 (0)1 45 68 17 64

UN-Water: 

Daniella Bostrom Couffe

daniella.bostrom@unwater.org

+41 79 159 92 17

More information:

World Water Day

https://en.unesco.org/commemorations/waterday