There is serious concern that China’s Three Gorges Dam may fail due to heavy flooding.
And that if it fails, it would kill millions of people, perhaps 100 million according to some claims, and displace even more. Up to ~400 million people live downstream of the dam.
It would arguably be the biggest non-pandemic disaster in history and have devastating second-order effects, including:
exacerbation of the coronavirus,
nuclear radiation worse than Fukushima,
further instability in Great Power dynamics, and
global economic depression/collapse.
It is no exaggeration to say that a sudden collapse of this dam could be the spark of cascading civilizational collapse. It is worth examining even if the risk is small.
From the National Review:
China has been suffering through record rains the past weeks, leading to the worst flooding in the country in decades. There is little relief in sight, and the Yangtze River is now above flood level, according to China’s Ministry of Water Resources. A few days ago, officials admitted that certain “peripheral” structures of the massive Three Gorges Dam deformed due to the building water pressure. Stunning pictures of water being released to relieve pressure are raising the specter of whether the entire dam could fail (some good photos here). Some online satellite photos purporting to show the buckling of the dam, however, should be viewed with skepticism.
Still, the damage that has already occurred from the record deluge is significant, with numerous cities upriver from the dam already flooded[...]
All that would be dwarfed if the Three Gorges Dam failed. The dam was built from 1994 to 2006, at a cost of $31 billion and displacing 1.4 million people for its construction, precisely to lessen the risk of devastating flooding along the Yangtze, a perennial problem in China since ancient times. The river’s basin accounts for nearly half of China’s agricultural output, and it runs through major cities, such as Wuhan, with 10 million people.
Chinese authorities have already evacuated 38 million people downriver. The dam can hold back waters to a level of 175 meters above sea level; according to the Bureau of Hydrology of the Chanjiang (Yangtze) Water Resources Commission, the latest (Friday) height at the dam was 158.85 meters, down from 164 meters on Tuesday. Yet more rain is predicted, and if smaller, older dams upriver from Three Gorges overflow or fail, then the pressure on the main dam could quickly overwhelm either its capacity or even its structural integrity.
While an outright failure of the dam may not be the primary danger, nonetheless its geopolitical consequences are staggering to contemplate. It would be a black swan of epic proportions, China’s Chernobyl moment. A tsunami-like wave from a breach in the Three Gorges Dam could wipe out millions of acres of farmland right before the autumn harvest, possibly leading to famine-like conditions. As it is also the world’s largest hydroelectric power station, a failure would lead to huge power outages. Low-lying cities of millions along the Yangtze’s banks cities could become uninhabitable and the death toll could be staggering.
What is the base rate of dams collapsing from heavy rains?
What is the average level of rainfall in China/the Yangtze river basin each year at a given period of time (particularly in the summer/the month of August)?
How much future rainfall is projected in the Yangtze river basin?
How much rainfall would need to fall in the Yangtze river basin in order for Three Gorges Dam to fail?
How many people would die if Three Gorges Dam collapsed?
How many people currently live within the area of projected flooding if Three Gorges Dam collapses?
How many deaths from starvation would occur if Three Gorges Dam collapsed?
How much food is produced in the path of projected floodwaters?
How many nuclear power plants would be destroyed?
What are second-order effects of Three Gorges Dam collapsing?
Here is the accompanying Metaculus question for this post (pending mod approval). Please submit estimates to it as well!
A good answer to this question displays original information, modelling, thinking, and also provides a probability estimate. I invite a plethora of amateur Fermi calculation reasoning. I do hope to see at least a handful of answers from people who are dam experts, engineers, hydrogeologists, physicists, weather forecasters, or otherwise have expertise in relevant domains.
$50 to the best answer to this question by the end of July, as judged by upvotes + personal judgement.
$25 ‘Fastest Updater’ prize, awarded at my discretion. This will be given to whoever is judged to have exhibited the most of some combination of: volume of contribution, most amount of justified changes to their probability estimate, collecting useful info, biggest update to their explicit models in either direction, causing the biggest update to others’ models, most amount of changes to other’s probability estimates. ‘Having lots of updates rather than one correct prior’.
Prize pool contributions welcome!