Extreme weather events increase as Earth warms


Extreme weather is common in Iowa and has always occurred throughout history. Prolonged heat waves and cold snaps, tornado outbreaks, a derecho and multiple flash flood events have occurred in the past few years, but they’re becoming more common and more intense. That means more Iowans are in danger. Think back to the July 9, 2021 hailstorm. 2” hail fell in several Iowa towns, but it all came from one storm. 

WHO 13 Chief Meteorologist Ed Wilson even expressed the rarity of a storm lasting this long while on air that afternoon. “We had this hailstorm that left a hail track from just south of Fort Dodge, all the way down south into Des Moines so you’re … talking about 70 miles of hail, without a big interruption,” Wilson said. 

Wilson also experienced an unprecedented flash flooding event back on June 20 2018, in which 10” of rain fell on the north side of the Des Moines metro. 

The increase in extreme events comes from how much Earth is warming. The Arctic or high latitudes are warming two to three times faster than the mid-latitudes. This has caused the temperature gradient between these areas to relax or weaken resulting in a slower and weaker jet stream. 

Iowa’s state climatologist, Justin Glisan, says the jet stream begins to bend in different ways and can cause some waves to stall out. “We’re seeing meanders form periodically and persistently so when we do see a meander form like Arctic intrusion from the polar vortex or in 2018 when we had the storm track stuck over northern Iowa 27 counties broke their precipitation records in November, annual precipitation records because the Jetstream was consistently parked over that part of the state,” says Glisan. 

Since 1895, the average temperature in Iowa has risen by about 1.3°. Because of this the atmosphere is actually able to hold about 4% more water vapor. Extra water vapor in the air can cause longer periods of drier but more humid weather, and Glisan says that’s especially true during July in Iowa. Glisan says, “The crop is maturing, livestock are in the hottest part of the year without regular rainfalls. So we do see increased livestock stress but also human stress given the decrease in the amount of rainfall that we see.”

More water vapor in the air also means there is a better chance of seeing heavier rain events when it does rain. The June 30, 2018 and July 1993 flood events are good examples of these heavier rain events. The 1993 flood was when Wilson first started to realize something bigger was happening in our climate. Thinking back to the flood of 1993 he said,  “All of this rain fell up near Jefferson. It was just making its way down so 10 inches of rain, all at once coming downstream and we have blue skies, so it was remarkable to see all this happen. That was my first foray I think into saying hey there’s obviously some changes happening, there’s something that we’ve never seen before. We were the first city of our size to be in the United States without water because of a flood event.” 

Glisan is more concerned about the increased frequency of these heavy rain events. “Because we have a greater propensity for more precipitation, given the trends that we’re seeing, the infrastructure that was built to protect us … the levees and dams … were built 80 to 100 years ago … in a different type of precipitation regime. So we don’t only look at the actual behavior we’re seeing, but we look at the infrastructure that is meant to mitigate catastrophic damage.”

Fixing damage caused by these extreme events costs a lot of money, and according to Climate Central, the number of billion-dollar disasters has grown significantly in the past 40 years. Just in Iowa there were less than ten billion-dollar disasters in both the 80s and 90s, but during the last decade that number was more than 25. Wilson says because of the increase in extreme events, the way we plan for the future is especially important. “Urban planning has to be adjusted because we’re going to see more extreme events,” said Wilson.

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