In a landmark study published today in the journal Science, experts warn that over half of the world’s largest lakes are experiencing water loss. As expected, the primary culprits are a warming climate and unsustainable human consumption patterns.
Fangfang Yao, the lead author of the study and a visiting fellow at the Cooperative Institute for Research in Environmental Sciences (CIRES), now a climate fellow at the University of Virginia, offers a silver lining amid the alarming data.
“This is the first comprehensive assessment of trends and drivers of global lake water storage variability based on an array of satellites and models,” says Yao.
Yao’s motivation to conduct the research originated from witnessing environmental crises in some of the planet’s largest water bodies, such as the drying of the Aral Sea situated between Kazakhstan and Uzbekistan.
To measure changes in water levels in almost 2,000 of the world’s largest lakes and reservoirs, Yao teamed up with colleagues from the University of Colorado Boulder, Kansas State University, France, and Saudi Arabia. These bodies of water account for 95 percent of the total lake water storage on Earth.
The researchers created an innovative technique that combines three decades of satellite observations with models to track and explain changes in lake storage on a global scale.
Freshwater lakes and reservoirs store 87 percent of Earth’s water, underscoring their importance to both human and natural ecosystems. Despite their significance, these lakes have been under-monitored compared to rivers, even though they supply more water to human communities.
“Until now, our understanding of long-term trends and changes to water levels has been largely limited,” said study co-author Professor Balaji Rajagopalan. “We are able to provide insights into global lake level changes with a broader perspective using this novel method,” he adds.
The team used a quarter of a million snapshots of lake areas captured by satellites from 1992 to 2020 to survey the area of 1,972 of Earth’s biggest lakes. They combined recent water level measurements with long-term area measurements to reconstruct the volume of lakes dating back decades.
The findings are sobering: 53 percent of lakes worldwide have seen a reduction in water storage. This loss equates to the volume of 17 Lake Meads, the largest reservoir in the United States.
To unpack these trends in natural lakes, Yao and his team drew on the latest advances in water use and climate modeling. Both climate change and human water consumption were found to be primarily responsible for the global net decline in natural lake volume, as well as water losses in about 100 large lakes.
“Many of the human and climate change footprints on lake water losses were previously unknown, such as the desiccations of Lake Good-e-Zareh in Afghanistan and Lake Mar Chiquita in Argentina,” said Yao.
Worryingly, lakes in both dry and humid regions globally are losing volume. This loss in humid tropical lakes and Arctic lakes indicates a broader drying trend than previously acknowledged.
In addition to studying natural lakes, Yao and his colleagues examined water storage trends in reservoirs. They discovered that almost two-thirds of Earth’s large reservoirs have undergone substantial water losses.
“Sedimentation dominated the global storage decline in existing reservoirs,” noted study co-author Professor Ben Livneh. For reservoirs established before 1992, sedimentation was found to be more impactful than either droughts or years of heavy rainfall.
However, not all lakes are shrinking. The study shows that 24 percent of global lakes have witnessed significant increases in water storage.
These expanding lakes are primarily located in underpopulated areas, such as the inner Tibetan Plateau and Northern Great Plains of North America, and in regions with new reservoirs, such as the Yangtze, Mekong, and Nile river basins.
The study’s authors estimate that approximately 2 billion people, or roughly one-quarter of the world’s population, live in the basins of these drying lakes. This striking statistic underscores the urgent need to consider the impacts of human consumption, climate change, and sedimentation on water management strategies.
While the news seems concerning, the study’s authors believe it could provide a pathway to potential solutions. According to Livneh, “If human consumption is a significant factor in lake water storage decline, then we can adapt and explore new policies to curb large-scale declines.”
The team’s research highlights one such success story: Lake Sevan in Armenia. Over the past two decades, Lake Sevan has witnessed an increase in water storage, a positive trend that the authors attribute to the enforcement of conservation laws restricting water withdrawal since the early 2000s.
In conclusion, the study marks a significant advancement in the understanding and tracking of global lake water storage trends. Though the results are worrying, they offer invaluable insights that could potentially guide policy changes and prompt more sustainable water use.
The findings underscore the urgent need for policymakers, water managers, and communities around the world to pay heed and take action to protect this critical resource and the vital ecosystems it supports.
Climate change is having a significant impact on Earth’s freshwater supply in several ways. Here are some of the most notable effects:
Climate change is altering the global water cycle, which affects where, when, and how much precipitation falls. Areas that are dry may become drier, and places that are wet may become wetter or experience more intense rainfall leading to flooding. Both scenarios can have serious implications for freshwater availability.
As global temperatures rise due to climate change, evaporation rates also increase. This leads to a reduction in the amount of surface water in lakes, rivers, and reservoirs, as well as groundwater in aquifers. Higher temperatures can also increase water demand from both humans and vegetation.
Many regions, particularly those in the western United States and parts of Asia, depend on runoff from snowmelt and glaciers for their freshwater supply. As global temperatures rise, glaciers are melting at an accelerated pace and winter snowpack is declining, leading to decreased water availability in spring and summer when it’s most needed.
As sea levels rise due to the melting of polar ice caps, saltwater can intrude into freshwater aquifers, particularly those near coasts. This phenomenon is known as saltwater intrusion and can contaminate drinking water supplies and agricultural lands, reducing the availability of freshwater for those purposes.
Climate change can impact the health of freshwater ecosystems. Higher water temperatures, changes in water flow, and increased prevalence of drought can stress or even kill fish, birds, and other wildlife that depend on freshwater habitats.
Climate change is expected to make droughts more frequent and severe in certain regions, reducing the availability of freshwater.
All of these factors pose significant challenges to managing water resources effectively and ensuring a sustainable freshwater supply for both human and ecological needs. It highlights the urgent need for implementing water conservation measures and developing resilient water management strategies in the face of a changing climate.
Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.