A recent assessment published in Science reveals that over 50% of the world’s largest lakes are experiencing a decline in water levels. The primary factors contributing to this trend are the warming climate and unsustainable human water consumption. However, lead author Fangfang Yao, a climate fellow at the University of Virginia, highlights a silver lining in the findings. The study’s innovative approach to tracking water storage trends and identifying their causes provides valuable insights for water managers and communities, aiding in the protection of crucial water sources and regional ecosystems.
Yao’s motivation for conducting this research stemmed from witnessing environmental crises in significant water bodies like the Aral Sea, which has been drying up between Kazakhstan and Uzbekistan. To address this issue, Yao collaborated with researchers from the University of Colorado Boulder, Kansas State University, France, and Saudi Arabia to develop a technique for monitoring water level changes in nearly 2,000 of the world’s largest lakes and reservoirs, which collectively account for 95% of the Earth’s total lake water storage.
Their methodology involved analyzing three decades’ worth of satellite observations and combining them with models to quantify and attribute global trends in lake water storage. Freshwater lakes and reservoirs globally store 87% of the planet’s water, making them a vital resource for both human and ecological systems. Despite their significance, long-term changes in water levels have largely remained unknown until now.
Balaji Rajagopalan, a professor of engineering at CU Boulder and co-author of the study, emphasizes the limited monitoring of lakes compared to rivers, despite their critical role in providing water to a substantial portion of humanity. The team’s innovative method enables a comprehensive assessment of global lake level changes and offers a broader perspective on the subject.
To conduct the analysis, the researchers utilized 250,000 snapshots of lake areas captured by satellites from 1992 to 2020, covering 1,972 of the Earth’s largest lakes. They gathered water level data from nine satellite altimeters, utilizing long-term records to minimize uncertainties. In cases where lakes lacked a long-term water level history, recent measurements from newer satellite instruments were used. By combining recent water level measurements with historical area measurements, scientists could reconstruct lake volumes dating back several decades.
The findings of the assessment are astonishing: more than half (53%) of lakes worldwide have experienced a decrease in water storage. To put this into perspective, the magnitude of this loss is equivalent to 17 times the volume of Lake Mead, the largest reservoir in the United States.
To understand the reasons behind these trends in natural lakes, the researchers utilized recent advancements in water use and climate modeling. They discovered that the global decline in natural lake volume and water losses in approximately 100 large lakes were primarily driven by climate change and human water consumption. Surprisingly, many of the impacts of human activities and climate change on lake water losses were previously unknown, such as the drying of Lake Good-e-Zareh in Afghanistan and Lake Mar Chiquita in Argentina.
Both dry and wet areas of the world are witnessing declines in lake volume. The losses observed in humid tropical lakes and Arctic lakes indicate more widespread drying trends than previously recognized.
The assessment also examined trends in reservoirs and found that nearly two-thirds of the world’s large reservoirs have experienced significant water losses. In existing reservoirs, sedimentation was identified as the dominant factor contributing to the decline in water storage, surpassing the impacts of droughts and heavy rainfall years, especially in reservoirs that were filled before 1992.
Although the majority of global lakes are shrinking, 24% of them have seen significant increases in water storage. The growing lakes are typically located in sparsely populated areas in the inner Tibetan Plateau and Northern Great Plains of North America, as well as regions with newly constructed reservoirs, such as the Yangtze, Mekong, and Nile river basins.
The authors estimate that approximately a quarter of the world’s population, around 2 billion people, live in the vicinity of a shrinking lake. This highlights the urgent need to incorporate the impacts of human consumption, climate change, and sedimentation into sustainable water resources management.
The research also offers insights into potential solutions. If human water consumption is a major contributing factor to the decline in lake water storage, adjustments can be made, and new policies can be explored to mitigate large-scale declines. An example of successful conservation efforts is observed in Lake Sevan in Armenia, which has experienced an increase in water storage over the past two decades due to the enforcement of water withdrawal conservation laws since the early 2000s.