by Welton Chang
Imagine getting an alert with the following headline: “Mosul Dam breaches; hundreds of thousands missing or dead.” The Mosul Dam lies to the northwest of the third largest city in Iraq, a country where U.S. forces have been engaged in some capacity since the invasion in 2003. Most people have never heard of the Mosul Dam and public interest in the potential for catastrophic collapse has been low (see Google Trends).
News coverage has also been sparse, save for a New York Times piece in January of last year and a few pieces that covered U.S. Ambassador to the UN Samantha Power’s public warnings in March. Most recently, Dexter Filkins published a piece in the New Yorker this month. If the dam were to collapse, impact estimates put the number of immediate deaths at around half a million and the water from the Tigris would put much of Mosul under as much as 15 meters of water. Without adequate warning and evacuation, the total number of dead and displaced could exceed 1.5 million, the functional equivalent of every single road-related death in the entire world for an entire year, except it would happen in a matter of hours.
Probability of Collapse
Right now, on Good Judgment Open, more than 230 forecasters put the probability of this event occurring in 2017 at around 6%. That means that if 2017 was simulated and played 100 times, the dam would collapse in six of those runs. But simulated worlds and counterfactuals being what they are (we live in only one), it may be more useful to put the risk of collapse in terms of odds. A 6% chance translates roughly to 9:1 odds, making the chances of a dam collapse the equivalent of basketball star Stephen Curry missing a free throw, or to drawing a jack from a full deck of cards. If you live in the United States, you are ten times less likely to die in a car accident in your lifetime. The forecasters on GJ Open put the odds of a dam collapse as roughly the same as North Korea not conducting a nuclear test in 2017.
The Outside View: Base Rate of Dam Collapses
An avid reader of this blog might ask: “How many dams usually collapse each year? And how many of those dams are of a type similar to the Mosul Dam?” True, the forecasted probability on GJ Open can be miscalibrated (since even if the dam doesn’t collapse in 2017, a 6% chance means no collapse should happen 94 out of 100 times). U.S. Government experts who have examined the dam assess it could collapse at any time, with little to no warning, and this risk will grow during the high water season in the spring. The true probability of a dam collapse is difficult to know, if not unknowable. One alternative estimate by the Iraqi Minister of Water Resources puts the chances of a collapse at closer to 0.1%, although based on the language used by experts such as the U.S. Army Corps of Engineers, the real number is almost certainly higher. While dam collapses in general are more frequent than most probably realize (there have been 82 since 1900), the only comparably catastrophic dam collapse in the last 117 years is that of the Banqiao and Shimantan Dams in China in 1975 which killed 171,000 people. Today, there are approximately 57,000 dams around the world and close to 300 dams similar in size to the Mosul Dam. So the probability of any one of them collapsing is very low. The low collapse rate has to do with solid construction, regular maintenance and with the fact that most dams aren’t located in a war zone.
The Inside View: What Makes the Mosul Dam More Dangerous?
Several problems specific to the Mosul Dam should inform and likely boost the estimate of a collapse over the overall rate. Because the Mosul Dam was built on a soft and ultimately unstable foundation, keeping it intact requires a careful and laborious grouting process, with technicians injecting tons of cement into large voids that regularly emerge inside the dam. This maintenance process is prone to interruption (like when ISIL briefly captured the Mosul Dam in August 2014). Even the efforts of the Trevi Group (an Italian company contracted to repair the dam) provide only a temporary fix — the only real way to prevent dam collapse is to decommission the Mosul Dam and build a new one at a place in the river with a solid foundation. Ultimately, a dam collapse is by no means impossible and it would be foolhardy to assume that the probability of a collapse is zero.
A Worse Problem Than ISIL?
So how bad of a problem is a dam failure? For the sake of argument, let’s assume the real probability is around 6%. This translates into an expected cost of around 40,000 lives, more than the total number of U.S. casualties during the Korean War. Even the aforementioned higher estimate of 1.5 million casualties is a lower bound estimate: a dam collapse would impact all of the Iraqi cities along the Tigris, including Baghdad. This would put nearly 7 million people at risk. The same number of people live in the state of Arizona. Standing water would bring diseases, corpses, and washed-up bombs into major urban areas, making cleanup a nightmare. International rescue efforts would be complicated enormously or even precluded in some areas, by ISIL’s continued presence.
The scale of a Mosul Dam collapse has been termed “epic”, “staggering”, and “Biblical”, and even these words don’t do justice to the potential for harm. Despite this, the dam still has not breached U.S. public consciousness. Part of the explanation might be psychological. It is well-documented that people do not fully understand the scale of events, in effect ignoring the zeroes in a number like 500,000 potential dead. We also tend to naturally discount the probability of terrible events, because for the most part, they don’t happen. People also process spatially and temporally distant objects different from those right in front of their noses — a dam collapse in far away Iraq, a place already plagued by awful events, may seem like an abstraction to most Americans. And there are many potential explanations for why an event like the Red Sox winning the World Series seems more plausible than a Mosul Dam collapse, even though the two have similar assessed odds. The image of a walk-off home run is vivid, and one that most of us have seen before. Very few of us have read much about dam collapses, let alone experienced one. These are the psychological barriers to taking a probability like 6% seriously.
Keeping Watch, Taking Action
Right now, Iraqi forces assisted by international advisors are reclaiming territory at the doorstep of West Mosul. If a dam collapse occurred during their push into the center of the city, Iraq’s elite counter-terrorism forces might get wiped out and the Iraqi Army would likely have to abandon all of their equipment. If U.S. and international forces advising Iraqi ones were in the vicinity of the Tigris River during a collapse, those lives might be lost as well. The permanent solution might best be implemented by the Iraqis with the assistance of an international coalition of funders (similar in composition to the countries currently taking the fight to ISIL). President Trump has yet to weigh in on the Mosul Dam issue, but even a 1% chance of a collapse should be taken quite seriously. That GJ Open forecasters think the chances are six times greater should give everyone pause, given the stakes. After all, forecasters can only tell you what they think. It is up to policymakers, both in the United States and in Iraq, to act appropriately.
Welton Chang is a psychology graduate student at the University of Pennsylvania and a Superforecaster for Good Judgment Inc. He is a former U.S. Army officer and Defense Department analyst who served two tours in Iraq. The views presented here are his own and do not necessarily represent those of his current or previous employers. Follow him on Twitter: @weltonchang