More than half of the world’s largest lakes and reservoirs are dwindling and placing humanity’s future water security at risk, with climate change and unsustainable consumption the main culprits, a study said Thursday. “Lakes are in trouble globally, and it has implications far and wide,” Balaji Rajagopalan, a professor at the University of Colorado Boulder and co-author of the paper, which appeared in Science, told AFP. “It really caught our attention that 25 percent of the world’s population is living in a lake basin that is on a declining trend,” he continued, meaning some two billion people are impacted by the findings. Unlike rivers, which have tended to hog scientific attention, lakes aren’t well monitored, despite their critical importance for water security, said Rajagopalan. But high-profile environmental disasters in large water bodies like the Caspian Sea and the Aral Sea signalled to researchers a wider crisis. To study the question systematically, the team, which included scientists from the United States, France, and Saudi Arabia, looked at Earth’s biggest 1,972 lakes and reservoirs, using observations from satellites from 1992-2020. They focused on larger freshwater bodies because of the better accuracy of satellites at a larger scale, as well as their importance for humans and wildlife. Their dataset merged images from Landsat, the longest-running Earth observation program, with water surface height acquired by satellite altimeters, to determine how lake volume varied over nearly 30 years. The results: 53 percent of lakes and reservoirs saw a decline in water storage, at a rate of approximately 22 gigatonnes a year.