Lakes are inland depressions filled with water. These represent standing, slow-moving bodies of water without swift currents, originating from a headwater and flowing into the sea. Lakes have vast surface areas that foster complex ecosystems, as the animals and plants living in such habitats have varying needs and environmental conditions. The planet has millions of lakes, and most are surrounded by stunning mountain ranges or desert plains, making them excellent tourist destinations.
The majority of the water on Earth, about 71%, is found in the oceans. The land-based water bodies are dispersed among different freshwater environments, including lakes, ponds, rivers, streams, and marshes. Here, a whole distinct environment coexists. The amount of water on Earth that can be used as drinking water is only about 1.2%. The remaining freshwater is trapped beneath the Earth's surface or in ice caps, permafrost, or glaciers.
Lakes help replenish groundwater, improve water quality downstream watercourses, and maintain local biodiversity and ecosystem. People can enjoy excellent lakeside recreational, tourism, and cottage or residential living opportunities. They provide the community with raw drinking water and are revered by many for their traditional and historical values. Lakes can also serve as a source of industrial water and agricultural irrigation, water bird habitat, and cycling of pollutants and nutrients.
The team of scientists from the University of Virginia and colleagues from the University of Colorado Boulder, Kansas State University, France, and Saudi Arabia created a technique to measure changes in water levels in nearly 2,000 of the world's biggest lakes and reservoirs, which represent 95% of the total lake water storage on Earth. They did this by combining three decades of observations from an array of satellites with models to quantify and attribute trends in global land water storage (GLWS), from 1992 to 2020 and then decouple the impacts of anthropogenic and natural factors on decadal-scale variability in lake water storage.
Their research paper published in Science (DOI: 10.1126/science.abo2812) showed that 53% of the most incredible freshwater lakes on Earth are in decline and are now retaining less water than they did thirty years ago, i.e. in the 90's. The study measured changes in water levels in roughly 2,000 of the largest lakes and reservoirs globally using satellite measurements spanning decades. It was discovered that human consumption, sedimentation, and climate change are to blame.
This GLWS collection contains sub-yearly storage time series for major water bodies that existed in 1972. These large water bodies included 1058 natural lakes (area: 100 to 377,002 sq km) and 922 reservoirs (area: 4 to 67,166 sq km), representing 96 and 83% of the Earth's natural lake and reservoir storage, respectively. Due to the accuracy of satellite measurements at this scale, the dominance of large lakes in influencing overall lake volume change, and the significance of large lakes for human and wildlife populations, only large lakes were considered in the study.
Using global dam and reservoir inventories, in-situ sediment surveys, and upscaling techniques, the researchers combine the consequences of recent dam building and subsequent reservoir infilling on reservoirs. They next distinguish between trends in lake storage in arid and humid environments and calculate the local population affected by lake water losses.
According to the study, over half (53%) of the big lakes suffered considerable water losses. Most of South America, western Central Asia, the Middle East, western India, eastern China, northern and Eastern Europe, Oceania, the contiguous USA (the lower 48 states in North America, including the District of Columbia), northern Canada, southern Africa, and most of South America all experience land water storage (LWS) loss. Approximately one-fourth (24%) of the significant lakes had considerable water gains, mainly found in areas where dams are being built and in places that are isolated or sparsely populated, such as the Inner Tibetan Plateau and the Northern Great Plains of North America. LWS revealed a net drop at a rate of 21.512.54 Gt per year globally.
On average, human activities or rising temperatures and potential evapotranspiration (PET, the combination of evaporation and transpiration) accounted for around one-quarter of the significant water losses in natural lakes, with the last changes most frequently attributed to climate change. Since lakes are hotspots of the carbon cycle, widespread LWS loss, particularly when combined with rising lake temperatures, might decrease the quantity of absorbed carbon dioxide and increase carbon releases to the atmosphere.
The fact that up to 2.0 billion people (one-fourth of the world's population in 2023) live in basins with sizable water bodies experiencing severe water storage losses has important ramifications for water resource management. Numerous of these drying lakes have been recognized as significant water and energy (hydropower) sources. About 24, 9, and 14% of the world's population reside in basins that are experiencing freshwater depletion, environmental deterioration, and a loss in hydroelectric production due to diminishing LWS.
Since sedimentation accounts for most water loss in existing reservoirs, as reservoirs age, the freshwater and hydroelectric energy they provide will become less reliable due to population dependence. In long-term planning for reservoir operations and building additional dams, sedimentation-induced storage water losses must be considered.
More than half of the net loss in natural lake volume (56%) is attributable to human activities and increasing temperature and PET, indicating that any recovery of water storage in these lakes could require substantial management, and practical water conservation efforts can help save these water bodies.
