Water in a Heated World

On Earth, water passes through a continuous, global cycle, which constantly provides fresh water in the form of precipitation over land. This is then available as blue or green water: blue water includes all water resources in rivers, lakes, reservoirs and groundwater; green water refers to the water held in the subsurface as soil moisture; through plants it can productively promote the formation of biomass. Eco systems and their biodiversity are an important part of the global water cycle.

Globally, agriculture accounts for 72 % of all freshwater abstraction, industry for 15 % and municipalities and households for 13 %. However, the amount of water abstracted for agriculture as a percentage of total abstraction varies considerably by region and income level. In high-income countries it is on average only 41 % of the total withdrawals, whereas in low- and middle-income countries water abstracted for agriculture accounts for 80–90 %. The expansion of irrigated agriculture, the area of which more than doubled between 1961 and 2018, and the water requirements of a growing urban population have led to the overuse of non-renewable groundwater (deep groundwater), and water tables have been falling further and further in many regions and cities around the world. The Middle East, North Africa, India, northern China and the Southwest of the USA are particularly affected. In most of these regions, water consumption for agricultural irrigation accounted for an average of over 90 % of total water consumption between 1960 and 2010. At least around half of this came from non-renewable groundwater.

Climate change and pollution: Climate change is intensifying the global water cycle: water is evaporating ever faster from the animal and plant world, as well as from soil and water surfaces, and the amount of water stored in the air is increasing – the air can store 7 % more water for every 1 °C of warming, making more and heavier precipitation events possible. Progressive warming is driving global and regional changes in precipitation and evaporation, shifting the balance from frozen to liquid water, increasing the water content in the atmosphere and leading to an increase in extreme events such as floods and droughts (Fig. 1 and 2).

Water quality, too, will continue to decline in the future if the discharge of inadequately treated waste-water – currently about 80 % of the world’s wastewater – and with it pathogens, persistent chemicals, nutrients and solid waste continues (Fig. 3).

Socio-economic and geopolitical developments: In future, unless effective actions are taken, water use – and thus the risk of overuse – will continue to grow, depending on the region. UNESCO (2023) estimates that the global demand for water will increase by about 1 % per year and thus by 20–30 % by 2050. However, the margin of error for this assessment is more than 50 %. A large proportion of the expected increase in demand will happen in low- and middle-income countries, especially in emerging economies.

These exacerbated water-related challenges can mutually reinforce each other and, in the medium and long term, escalate into regional water emergencies with a planetary dimension. The extent and dynamics of these water emergencies can exceed hitherto manageable risks. Here, the WBGU describes five examples of regional water emergencies whose patterns can also be found in other regions of the world.

In the last twenty years, over 80 large cities and metropolitan regions worldwide have been affected by severe water short-ages. The number of reports about cities threatening to run out of water is growing. In 2016, over 30 % of the urban population lived in areas where water was scarce (Fig. 4).

By global comparison, the MENA region (Middle East and North Africa) will be one of the most severely affected by the negative effects of climate change. Between 2007 and 2018, the availability of renewable fresh water per capita in the region fell by approximately 24 %.

After the poles, the glaciers of the Hindu Kush- Karakoram-Himalayan mountain range are the largest frozen freshwater reservoirs on Earth. The region’s river basins supply almost two billion people with water, i.e. a quarter of the world’s population. Even without further warming, a loss of more than 20 % of the ice mass and glaciated area in the mountain range is projected by 2100; this proportion increases to up to 65 % under different climate scenarios.

Globally, the number of people affected by water pollution from organic compounds could increase from 2.7 billion to up to 4.2 billion by the end of the century. Similar patterns are predicted for contamination by pathogenic microorganisms, salts and nutrients. This particularly affects Sub-Saharan Africa.

The risk of local water shortages has grown significantly in the Central Valley in recent decades due to rising demand and climate change. Groundwater loss has exceeded the rate of recharge on a multi-year average. As a result, more than 75 % of the wells suffered a lowering of the groundwater table by more than 1.5 m in 2018–2023.

In order to maintain a safe distance from the limits of controllability, measures are required at the global, regional and local level (Fig. 5):

First, it is important to limit the exacerbation of challenges which, as global drivers, have a direct impact on the global water balance: this requires an ambitious climate policy, including compliance with the goals of the Paris Agreement, as this is the only way to limit the changes to the global and local hydrological balance caused by climate change. Equally important is the implementation of the Kunming-Montreal Global Biodiversity Framework in order to protect the fundamental role of nature in the global hydrological balance. The earlier action is taken, the more options there are.

Second, regional water emergencies must be avoided as far as possible. If the exacerbated water-related challenges cannot be controlled, the likelihood of regional water emergencies on a planetary scale will increase. Transformative adaptation measures and climate-resilient, socially balanced water management are needed as defence against such emergencies, since incremental adaptation measures will no longer be sufficient. This requires a willingness to radically change course, in particular by shaping structural change, for example in land-use, industrial, settlement and infrastructure  policy – both nationally and in the context of international cooperation.

In many places, overuse of water resources, unequal distribution, loss of ecosystem services, and water-related health risks are partly caused by misguided and ineffective water management. Management approaches aimed at overcoming shortcomings and deficiencies, such as the established Integrated Water Resources Management (IWRM) approach, do not yet meet the challenges of climate change. The WBGU recommends establishing a new approach to water management that aims to live with – but also to minimize – uncertainty (Fig. 6).

Solution-space ecosystems: The restoration of wetlands such as swamps and marshes, river and floodplain landscapes or peatlands, as well as other water-relevant ecosystems such as forests, plays an important role in climate-resilient water management. Since the pre-industrial era, it is estimated that more than 80 % of the world’s wetlands have been lost due to changes in land use and drainage, and most of the remaining wetlands have been degraded.

Solution-space agriculture: On the one hand, climate-resilient water management in agriculture means adapting crops and cultivation methods (and irrigating where or when necessary) in order to deal with fluctuations in water supply and climate change as a whole. On the other hand, agricultural practices in turn also influence the water balance and water supply; agriculture must therefore contribute to a climate-resilient landscape water balance. Approaches to reducing water-related risks are diverse and locally specific, their effectiveness declines as climate change increases and is subject to uncertainties.

Solution-space cities: The WBGU recommends establishing climate-resilient urban water management across the board in accordance with the guiding principle of water-sensitive urban development. Together with access to affordable, climate-adapted housing, it is of key importance for a sustainable urban design for all in the future. In this context, the urban infrastructure must be designed in such a way that it is more resilient to the effects of extreme events and strengthens the local hydrological cycle, enabling it to act as an efficient buffer against growing water extremes.

The quality of water resources is severely impaired worldwide by the release of pollutants and pathogens. In many cases, the use of water as a transport medium leads to considerable concentrations of pollutants in the water. This regularly over-stresses nature’s self-purifying power. It is therefore essential to protect water quality in order to counteract the scarcity of water resources as a result of the exacerbated challenges.

The European Green Deal already includes the goal of ‘zero pollution’ by 2050. Zero pollution means that pollution is reduced to a level that is no longer harmful to human health and the health of ecosystems. The zero-pollution objective is of great importance and requires the implementation of a circular economy (Fig. 7).

Forward-looking water governance that is capable of learning and adapting is required to avoid harming humans and nature and to prevent distribution conflicts (Fig. 8 and 9).

Take responsibility internationally – develop an International Water Strategy: The WBGU recommends developing an International Water Strategy as a new impulse for water diplomacy. The aim here is to contribute to institutionalizing the existing processes on water as an exchange and coordination platform. The International Water Strategy should recognize the protection of water as a common concern of humankind and also address the use of green water and its possible regulation under international law.

Create policy coherence internally and externally: As part of their international political actions, Germany and the EU should establish policy coherence between the various external policy fields related to water as well as between the external and internal fields.

Shape trade and economic relations, hold the private sector responsible: International economic relations and trade policy should promote sustainable water use and not exacerbate water scarcity in regions suffering water stress. This requires better integration of water-related impacts and risks within the framework of international trade policy.

The proactive state: The state should play a proactive role in the field of water governance. In order to do justice to the precautionary and polluter-pays principles, democratic processes are needed to negotiate, conceive and implement strategies and instruments for water policy. Cooperation with different actors is important (‘with and not against society’), but this must not mean that the state withdraws and remains passive vis-à-vis the challenges of water governance. The WBGU recommends increasing administrative capacities and resources so that states can assume their role and responsibilities appropriately.

Promote self-organization at the regional and local level: Especially in regions of the world that are severely affected by exacerbated water-related challenges, the WBGU advocates the targeted promotion of structures that (1) enable self-organization at the regional and local level (bottom-up), (2) compensate for weaknesses in formal water governance, which is often designed by the state, and (3) also acknowledge and address deficits in informal systems.

International alliances for climate-resilient water management: When drawing up funding lines in the field of water management and water research, specific attention should be paid to promoting cooperative research projects with countries facing increasing challenges in water management, or affected by social polarization and political autocratization processes – or which are of high strategic relevance as partners and alliances for Germany and Europe at the level of geopolitical negotiation processes.

Mobilize and organize funding also for local approaches: Public and private investment is needed to finance this. More private capital in particular must therefore be mobilized, especially in low-income countries, where, for example, only 1.4 % of the private financial resources leveraged with development cooperation funds in 2012–2017 were allocated to the water and sanitation sector.

Science and education for a sustainable WaterFuture: The science system has a key role to play in dealing with exacerbated challenges. Especially the non-stationarity of hydrological regimes caused by anthropogenic climate change requires the continuous production of knowledge and data, which must be taken into account in innovations to ensure that the water requirements of humans and ecosystems are secure.