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April 4, 20255 min readThe Crucial Role of Damage Surveys in Tornado ScienceDamage surveys provide crucial information about when, where and how strong U.S. tornadoes are to better understand disaster riskBy Andrea Thompson edited by Dean VisserStructural damage is visible at Christ Community Church after a tornado struck on April 3, 2025, in Paducah, Ky. Michael Swensen/Getty ImagesThe U.S. National Weather Service forecasts tornado outbreaksoften days in advanceand issues the watches and warnings that help people know when and how to prepare and when to take cover. NWS researchers also perform another task that is less recognized but crucial: conducting damage surveys in the wake of tornadoes such as those that struck parts of Arkansas, Tennessee, Kentucky and Indiana this week.To learn more about why these surveys of the devastation wrought by tornadoes is so important, Scientific American spoke with tornado researcher Jana Houser of the Ohio State University.[An edited transcript of the interview follows.]On supporting science journalismIf you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.Why do researchers conduct damage surveys after a tornado hits?The biggest reason is to develop a climatological database for when tornadoes are occurring, where tornadoes are occurring and how intense tornadoes are.With a hurricane, you send a hurricane hunter aircraft in the air, and it drops an instrument package called a dropsonde through the hurricane. That instrument, as it is descending, acquires information about the temperature, the pressure, the winds, the moisture, etcetera. And those wind measurements are what we use to understand how intense the hurricane is.Tornadoes pose a challenge with this type of technique because theyre very small. Theyre also very intense, and theyre very difficult to predict. And oftentimes they dont occur anywhere where we could even put an instrument in it in the first place. So the best way we have available to us to determine how intense tornadoes are is looking at how much damage is caused by the tornado after the fact.A lot of people try to argue, Well, why dont we use radars, for example, to look at tornadoes? And the biggest problem with radars is the distance between the radar and the tornado. Also, where the radar is actually measuring in the tornado is not at the groundit tends to be very high. And theres not a standard height that we can always get information at, so we cannot compare apples to apples by using radar data.What does a damage survey involve?When you actually go to perform a damage survey, the first thing we want to do is figure out where the tornado started causing damage in the first place. So you want to establish a start point, and that is typically informedat least as kind of a first-order guessby radar data.Ive seen bits of straw stuck into the concrete berms of sidewalks. Jana Houser, tornado researcherWe have a list of 28 damage indicators, where we have very specific types of buildings and other objects. This is going to be, like, a hospital or a house or a gas station with an awning or a hardwood tree or a softwood tree. Meteorologists have worked intimately with civil engineers and wind engineers, using wind tunnels and tornado simulators and all of this fancy stuff, to really figure out, like, How much wind does it actually take to suck a roof off of a house? So [the amount of damage to] each one of those objects has a wind speed category associated with it [on the Enhanced Fujita (EF) scale]: EF1, EF2, EF3, etcetera. We use what we know about the damage incurred to back calculate the winds. We put all the various pieces together at the end of the day, and the rating assigned to a tornado is based on the most intense damage across the entire path of the tornado.Can you tell us about some of your experiences with damage surveys?Ive seen some interesting and kind of frankly gruesome things with these. I think some of the most memorable moments were after the Greensburg, Kan., tornado in May 2007. That was the very first EF5 tornado of the whole new EF scale that happened in 2007 [when it replaced the former Fujita scale].That was my first real experience with catastrophic tornado damage. The town was just leveledlike, 90 percent of the town just was wiped off the map. There were buildings where the slabs were just basically bare. There was a fire hydrantI will never forget thisthis fire hydrant was literally sucked out of the ground with, I dont know, at least six feet of pipe. And nothing was bentit was, like, perfectly straight. That just speaks to the intensity of the vertical winds that happen. You dont just have horizontal winds in a tornado.And Ive seen road scouringthis is when the tornado basically sucks pavement up off of roads. And Ive seen bits of straw stuck into the concrete berms of sidewalks. When you make that into a projectile thats moving 200-plus miles per hour, it has enough impact to literally stick into the side of a curb.If meteorologists cant get out right away to do a survey, or cant do so at all, can they use photographs?It all depends on the quality of the photograph and what the photographer knows or doesnt know about damage surveys. If you have someone out there who knows what theyre looking for and is zooming in on, for example, the connections between floor joists and the foundation [which can tell them how much wind a structure should be able to withstand], you can get a pretty good feeling for the damage.The challenge with photographs is that theyre point sources. Youre not necessarily guaranteeing full time-space coverage, unless theyre really doing thousands and thousands of pictures from different angles.And then, obviously, the challenge with not getting a damage survey crew out immediately is that people start cleaning up immediately, muddying the waters a little bit.How crucial is it to always do these surveys?Damage surveys are critically important to informing our U.S. tornado climatology. If we stop having the ability to go out and actually do damage surveys consistently, that is going to throw off our whole understanding of whats happening with tornadoes in time.We could get a false sense that there are fewer tornadoes because we dont have crews that are actually going out to survey some of these weaker tornadoes. Or, if offices are pressed for time, we might end up actually getting inaccurate EF scale ratings because they are short-staffed and are dealing with limited resources.This, then, has implications on the big question that everybody wants to know, which is: How are tornadoes changing in a world of a changing climate? If we dont have adequate data, we cant answer that question accurately.
