‘Water Management: 3 minutes to understand’ the water cycle and the nature-based solutions

To mark its 35th anniversary, the International Water Agency has launched a video series entitled ‘Water Management: 3 Minutes to Understand’ to raise awareness of water issues in the context of climate change and increasing pressure on natural resources. These three-minute videos aim to explain sometimes complex topics in accessible terms to a wide audience, ranging from professionals to the general public.

The first episode addresses Integrated Water Resources Management (IWRM), a systemic approach that the OiEau has been promoting for over 35 years. This approach helps to reconcile human uses with the preservation of ecosystems, by supporting governments and river basin organisations in implementing concrete solutions.

The second episode of the series addresses water and sanitation, two issues vital to public health, recognised as human rights by the UN since 2010 and incorporated into Sustainable Development Goal 6.

The water cycle refers to the natural and continuous process by which water circulates between the Earth, the atmosphere and the oceans, in its three physical states: liquid, solid and gas.

This closed system, on a global scale, has maintained a constant total volume of water on Earth for billions of years, although its distribution varies according to climatic and environmental conditions.

It relies on several interdependent processes:

• Evaporation, driven by the sun, transforms liquid water from the oceans, lakes and rivers into water vapour. Added to this evaporation is plant transpiration; together, these are referred to as evapotranspiration. Around 90% of global evaporation comes from the oceans, which cover more than two-thirds of the Earth’s surface.
• At higher altitudes, water vapour cools and condenses to form clouds, composed of droplets or ice crystals.
• When these particles become too heavy, they fall as precipitation: rain, snow or hail, depending on weather conditions.
• Once on the ground, the water follows two main paths: some seeps directly into the soil to replenish groundwater, whilst the rest runs off the surface, gradually flowing into rivers, lakes and, ultimately, the oceans.

Today, the water cycle is facing unprecedented disruptions, mainly linked to global warming and human activities.

Rising global temperatures – 2015–2025 were the 11 warmest years on record – are accelerating the hydrological cycle, with increased evaporation, according to the study ‘Global Climate Highlights 2025’ published by the European Centre for Medium-Range Weather Forecasts in January 2026. This intensification results in heavier rainfall, more frequent flooding, but also prolonged droughts in certain regions.

The melting of ice, particularly at the poles and in the mountains, is contributing to rising sea levels, which have risen by 20 cm since 1900, including an average of 10 cm in the period 1993–2020 alone.

Source: EU Copernicus Marine Service Information, Time series of mean sea level, data extracted in September 2022. Processing: SDES, 2022.

Furthermore, rising temperatures are gradually reducing their ability to absorb carbon dioxide (CO₂), which, as the planet’s main natural carbon sink, contributes to rising CO₂ concentrations in the atmosphere.

At the same time, the over-exploitation of water resources, the pollution of rivers and groundwater, and the sealing of land, which reduces water infiltration capacity, are exacerbating the risk of shortages.

According to the European Commission, global water demand will exceed available resources by 40% by 2030, whilst 50% of the world’s population (around 4 billion people) faces high water stress for at least one month of the year (United Nations World Water Development Report 2026).

In light of these challenges, regulating the water cycle is a global priority, and Nature-based Solutions (NBS) are emerging as an innovative and sustainable response to restore its natural balance. Defined by the International Union for Conservation of Nature (IUCN) as actions aimed at protecting, sustainably managing and restoring natural or modified ecosystems, NBS draw on ecological processes to address water management challenges, promoting biodiversity and human well-being.

Nature-based solutions have a direct impact on the fundamental mechanisms of the hydrological cycle: evaporation, condensation, precipitation, infiltration and runoff. By restoring or enhancing the natural functions of soils, wetlands, watercourses and vegetation, they help regulate water flows, improve water quality and strengthen the resilience of regions to extreme weather events. In addition to regulating the water cycle, they also improve water quality by reducing the transport of pollutants into aquatic environments.

These approaches are part of an integrated water resource management strategy, in which nature becomes an ally in mitigating the effects of climate change.

Disruptions to the water cycle call for adaptive solutions, and Nature-based Solutions offer environmentally friendly and effective ways of addressing these challenges, whether in urban or rural settings.

Beyond the technical solutions they provide, NBS are playing an increasingly important role in public policy relating to water management. As such, local authorities, water management bodies and other economic stakeholders are encouraged to incorporate them into their planning and management strategies.

In addition to their positive effects on ecosystems, these approaches also generate numerous social and economic benefits. Their contribution to regional resilience explains why they are now recognised, both in France and at European level, as key drivers for preserving aquatic environments and strengthening adaptation to climate change.

The transition towards more sustainable water management also relies on raising awareness, sharing knowledge and building capacity. With this in mind, OiEau produces the podcast ‘Les Petits Ruisseaux’, which highlights inspiring nature-based initiatives and gives a voice to experts, local authorities and project leaders committed to preserving water resources. Accessible to a wide audience, this format helps to improve understanding of water-related issues and to promote practical solutions being implemented across the country.

This initiative is accompanied by a range of training courses designed for practitioners in the field. Through courses dedicated to the Management of Aquatic Environments and Flood Prevention and Integrated Rainwater Management, OiEau supports local authorities and professionals in acquiring the skills needed to design and implement effective adaptation strategies. In particular, these training courses promote greater consideration of nature-based approaches in water planning and management policies.

The provision of reliable data is another cornerstone of sound water resource management. In this regard, the Cartographic Atlas of Hydrological Situation Bulletins (only in French), developed by OiEau, provides an overview of the state of water resources across France. By facilitating access to up-to-date information on groundwater, watercourses and rainfall, this tool helps decision-makers anticipate water stress and adapt their actions to local conditions.

To support the move towards action, OiEau also provides a series of guidance sheets on Natural Water Retention Measures (NWRMs) - only in french. These resources offer practical guidance on how to implement solutions that promote water infiltration, storage and natural regulation, whilst highlighting their benefits for local areas and ecosystems.

This commitment is also reflected in the development of european projects aimed at strengthening the resilience of regions to the impacts of climate change. Coordinated by OiEau, the SpongeScapes and NATALIE projects exemplify this approach by drawing on Nature-based Solutions to restore the capacity of ecosystems to retain, store and release water. By promoting the strengthening of regions’ ‘sponge’ function, these initiatives help to limit the effects of droughts, mitigate flood risks and better cope with extreme hydrometeorological events. They also contribute to the emergence of new adaptation methods, bringing together local stakeholders, researchers and decision-makers around concrete and replicable solutions.

Innovation is also a key driver in addressing the water challenges of the future. Through the European OPTAIN project (Optimal Strategies to Retain and Re-use Water and Nutrients), OiEau is involved in developing and evaluating natural water retention measures in small agricultural catchments. Rolled out across fourteen European countries, this initiative aims to strengthen regions’ capacity to cope with both droughts and heavy rainfall, through decision-support tools, best-practice catalogues and learning mechanisms that encourage the adoption of appropriate solutions.

Finally, the sharing of lessons learnt and proven methods remains essential to facilitate the scaling up of these approaches. The handbook *Basin-Connected Cities*, published by the International Network of Basin Organisations (INBO), for which OiEau provides the permanent technical secretariat, forms part of this initiative. Drawing on numerous international examples, it proposes concrete courses of action to strengthen the links between cities and their catchment areas, and to promote more integrated water governance that reconciles territorial development, resource conservation and adaptation to climate change.

NBS represent a promising approach to reconciling resource conservation, climate adaptation and biodiversity protection. Their large-scale deployment, supported by regulatory frameworks and dedicated funding, could help restore balance to the water cycle whilst meeting the growing needs of human societies.

By working with nature rather than against it, NWS pave the way for a more harmonious and sustainable approach to water management, where ecosystems play a central role in regulating flows and protecting this vital resource.