The collapse of two dams in Libya, unleashing torrential floodwaters that left at least 3,000 people dead and over 4,200 still missing, was both predicted and preventable. And they won’t be the last big dams to collapse unless we remove and repair some of the aging and obsolete structures that are long past their expiration date.

Like many dams around the world, the Wadi Derna dams in Libya were built in the 1970s during the era of peak global dam construction, when 1,000 large dams were installed each year. Now most of these dams are reaching the end of their life spans.

Details are still emerging, but the Libya dam collapses appear to have been caused by poor maintenance, and by poor monitoring of reservoirs that were overwhelmed by a huge rainstorm. Critical warnings were issued last year about the dams’ deteriorated state and the repairs needed to avert such a scenario, yet no action was taken.

Similar disasters are waiting to happen around the world. The biggest danger is in India and China, where the 28,000 large dams built in the mid-20th century are now nearing obsolescence. Mullaperiyar Dam in Kerala, India is over 100 years old, visibly damaged and located in a region prone to earthquakes. Its collapse would harm 3.5 million people downstream.

In the United States, the second most prolific dam-builder after China, the average age of dams is 65 years old and an estimated 2,200 structures are at high risk of collapse. The recent infrastructure law directs $3 billion into maintaining some of them, but there are still thousands of dams the federal government is not responsible for, and it will cost an estimated $76 billion to fix them.

The risks from aging dams are of particular concern in the face of climate change. Dams are designed to withstand worst-case conditions as they can be imagined at the time of construction. But what were once considered once-in-a-century weather events have begun occurring with increasing regularity, putting dams at great risk of either failure or a significant weakening of their integrity.

Before the disaster in Libya, extreme weather worsened by climate change was already taking its toll on these structures. Heavy rainfall damaged California’s aging Oroville Dam in 2017, prompting mass evacuations amid fears of major uncontrolled releases. A piece of a Himalayan glacier destroyed one dam and damaged another in northern India in 2021, killing dozens of people. Glaciers melting rapidly as a result of warming are now a major safety hazard to da