Science

30. September 2025

World's lakes show severe climate fingerprint as the global water crisis deepens

European satellite data reveal how space-based monitoring supports critical water resource assessments

The world experienced mounting water stress in 2024, with the hottest year on record triggering complex patterns of drought and flooding that affected freshwater systems from surface lakes to agricultural soils worldwide. The World Meteorological Organization's (WMO) State of Global Water Resources 2024 report, published on 18 September, provides a detailed overview of a planet experiencing mounting water stress. The fourth annual assessment shows that nearly all of the world's major lakes recorded water temperatures well above normal despite highly variable water levels, while soil moisture patterns revealed stark regional contrasts – from severe drying across South America to excessive moisture in Central Europe. River discharge deviated from normal conditions in approximately 60% of global catchment areas for the sixth consecutive year, while severe drought persisted across major basins in South America, including the Amazon. Meanwhile, widespread flooding affected regions from Central Europe to western Africa.

ESA Climate Change Initiative fills critical data gaps

With its Lakes project, the European Space Agency's Climate Change Initiative (ESA CCI) contributed global satellite observations to the WMO assessment, helping to address critical gaps in the monitoring of global freshwater. The project tracks 75 major bodies of water worldwide, providing unparalleled global coverage of freshwater resources, to complement ground-based monitoring – and gives global coverage including remote and inaccessible regions.

“Satellite observations form the backbone of long-term and accurate climate data records that inform international assessments and policy decisions,” says Dr Clement Albergel, Head of ESA's Actionable Climate Information Section. “These global, decades-long records equip scientists with the essential baseline they need to track how Earth's freshwater systems respond to our changing climate.”

Surprising temperature patterns override regional variations

A striking finding from the lake monitoring reveals contrasting patterns between water levels and surface water temperatures. Despite highly variable precipitation and water availability across different regions, temperatures in nearly all of the 75 monitored lakes were well above historical norms in July 2024, affecting water quality. Only a few exceptions with normal or below normal temperatures were recorded in Central and South America, Sweden, eastern China and across the northern United States.

In contrast to the uniform increase in temperature, water levels revealed more complex regional trends, with Canadian lakes experiencing much below normal levels, most major African lakes recording much above normal conditions, and significant water deficits across the Middle East and Central Asia. Northern European and Russian lakes generally maintained above normal levels.

“These findings highlight the crucial role of continuous satellite monitoring in water resource management,” says Beatriz Calmettes, Project Officer of the Lakes project. “The combination of rising temperatures and fluctuating water levels creates complex challenges that can only be addressed with the global perspective that space-based observations provide.”

Global implications for water security

The findings of the 2024 WMO State of Global Water Resources report have significant implications for freshwater ecosystems and human water security. Warmer lake temperatures accelerate evaporation and affect water quality and abnormal hydrological conditions across multiple systems illustrate how water stress propagates throughout entire watersheds.

These challenges are unfolding against a backdrop of growing global water insecurity. According to UN Water, an estimated 3.6 billion people currently face inadequate access to water for at least one month per year, a figure which is expected to rise to over 5 billion by 2050.

As climate change accelerates and water-related extremes intensify, the suite of long-term satellite records generated by research teams contributing to ESA's Climate Change Initiative provides governments and international organisations with the essential evidence base they need to develop effective mitigation and adaptation strategies for our planet's most precious resource. With many of its projects generating a suite of satellite-derived data records that address hydrological Essential Climate Variables including “soil moisture” "River Discharge", "Anthropogenic Water Use" or "Sea Level", ESA CCI provides observations that can contribute significantly to global assessment, deepen understanding and provide early warning of change across the water cycle.

About the State of Global Water Resources 2024 report

The WMO publishes a suite of reports that deliver intelligence and insights, including the annual State of Global Water Resources Report. The report serves as an authoritative evaluation of worldwide freshwater resources, encompassing streamflow, reservoirs, lakes, groundwater, soil moisture, snow and ice. It is based on data contributed by WMO Members, as well as information from global hydrological modelling systems and satellite observations from a wide range of partners. The report is designed for government agencies, policy makers, hydrologists, climatologists, and international organisations working on water security and climate adaptation.