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Record rain in St. Louis is what climate change looks like

Posted on 1 August 2022 by Guest Author

This is a re-post from Yale Climate Connections by Bob Henson and Jeff Masters

Torrents of rain that began before dawn on Tuesday, July 26, gave St. Louis, Missouri, its highest calendar-day total since records began in 1873. And the deadly event is just the latest example of a well-established trend of intensifying downpours in many places across the globe.

The official reporting site at Lambert International Airport received 8.6 inches of rain from midnight to 11 a.m. Central Standard Time on Tuesday. (Standard time is used year-round to separate calendar days for meteorological data purposes.) Another 0.46 inch had been recorded just before midnight CST on Monday, bringing the total for July 25-26 to 9.04 inches as of 11 a.m. CST Tuesday.

The predawn onset of the storms meant that many residents were startled awake by floodwaters or caught on highways during early commutes. Dozens of water rescues were carried out across the area. The storm closed Interstate 70 and many other key roads across the St. Louis area throughout the morning, according to the St. Louis Post-Dispatch. At least one death has been reported as of Tuesday evening, a person pulled from an inundated vehicle.

More heavy rain is possible early Wednesday, although the storms in that round are expected to keep moving rather than stalling out.

Below are several records set in Tuesday’s brief but intense deluge. Update (3:30 pm CDT Wednesday): The numbers below now reflect observations from St. Louis Lambert International Airport for Monday through Wednesday morning, July 25-27. We will provide another update if additional rain falls before midnight Wednesday night.

  • Heaviest rainfall in a 24-hour period, including periods that straddle calendar days: 9.07 inches from Monday night thru Tuesday morning (old record 7.02 inches on August 19-20, 1915, from the remnants of the 1915 Galveston hurricane)
  • Heaviest rainfall for one calendar day: 8.64 inches on July 26 (old record 6.85 inches on August 20, 1915).
  • Heaviest rainfall for two calendar days: 9.54 inches on July 26–27 (tied with 9.54 inches on May 16-17, 1995)
  • Heaviest rainfall for three calendar days: 9.97 inches on July 25–27 (old record 9.78 inches on May 16-18, 1995)

Figure 1 rainfall totalsFigure 1. The 24-hour total of just over 9 inches in St. Louis would be expected to occur about once every 200 to 300 years if the climate were “stationary,” based on the NOAA Atlas 14 catalog of recurrence intervals. Atlas 14 is based on past observed rainfall, so it does not take ongoing climate change into account. Recurrence intervals are most likely getting shorter in many locations. (Image credit: NOAA Atlas 14)

Figure 2 satellite imageFigure 2. The cold, high tops of an intense mesoscale convective system that tracked across the St. Louis metropolitan area on July 26, 2022, can be seen in this infrared satellite image from 0800Z (3 a.m. CDT) Tuesday, with a particularly intense core (dark red) stretching from west to east across the St. Louis area. (Image credit: RAMMB/CIRA/CSU)

The culprit behind the early-morning deluge was a mesoscale convective system — a large, highly organized complex of showers and thunderstorms — that moved across the area in a “training” fashion from west-northwest to east-southeast, with cells regenerating and tracking along a constant path while the complex itself moves much more slowly. The system included one band of intense rainfall passing directly over St. Louis, with a secondary band roughly 60-70 miles to the north. Some areas just northwest of St. Louis may have seen as much as 14 inches of rain.

Update (3:30 p.m. Wednesday): CoCoRaHS stations in the St. Louis area reported the following impressive one- and two-day totals through Tuesday and Wednesday morning, respectively.                                                           

2.2 miles NE of St. Peters:  12.34 in., 14.69 in.
3.9 miles NNW of O’Fallon 10.58 in., 11.83 in.
1.2 miles ESE of Maryland Heights: 10.35 in., 11.87 in.

Figure 3 Hydrograph for Dardenne Creek near St LouisFigure 3. Hydrograph for Dardenne Creek near I-70 in St. Louis. In the seven hours beginning at 12:30 a.m. July 26, the creek rose 21 feet, and peaked just 1.36 feet below the all-time record set on September 15, 2008. (Image credit: NOAA)

The Midwest is getting more rain — and more extreme rain events

Although the Midwest climate is naturally drought-prone, recent decades have trended more toward the wet side of the spectrum. “Annual precipitation in the Midwest has increased by 5% to 15% from the first half of the last century (1901–1960) compared to present day (1986–2015),” the Fourth National Climate Assessment observed in 2018.

There’s a well-established trend in many parts of the globe for the heaviest short-term rainfall events to become more intense, consistent with a human-warmed atmosphere allowing more moisture to evaporate from warmer oceans and to flow into rainmaking systems. Over the past 120 years, the Midwest has seen a 42% increase in the amount of rain falling in top-end short-term rainfall events (the heaviest 1% of events). That was larger than any other region of the country for the period 1901-2016, although it was surpassed by the Northeast in the period 1958-2016 (see tweet below, which includes a National Assessment analysis).

“Storm water management systems and other critical infrastructure in the Midwest are already experiencing impacts from changing precipitation patterns and elevated flood risks,” the National Climate Assessment, a sweeping government report on the impacts of climate change in the United States, noted in 2018.

As one of the 10 biggest U.S. cities between 1850 and 1960 — but only the 70th-largest as of 2020 — St. Louis joins other venerable but now-smaller U.S. cities in having to adapt major century-old infrastructure to the evolving climate of the 21st century. As noted in the National Climate Assessment, the Metropolitan Sewer District in St. Louis had embarked upon a $100 million “rainscaping” project designed to divert storm water runoff in the northern portion of the city of St. Louis and adjacent north St. Louis County, including areas where the July 26 storm tracked.

Significant flood threat for Kentucky and West Virginia this week

The stalled frontal boundary that brought St. Louis its record flooding will be draped over the Ohio River Valley through Friday, bringing an elevated threat of flash flooding across portions of Kentucky and West Virginia. On Tuesday evening, this area was been placed under a moderate-risk threat of excessive rain leading to flash flooding. The threat extended across a 48-hour period from Wednesday through Friday morning by the National Weather Service, which is predicting widespread rainfall amounts of 2-4 inches on Wednesday and 1-3 inches on Thursday. This area has already seen significant flash flooding during the past few weeks from extreme rainfall; however, soil moisture levels are currently near average.

This region, which is highly mountainous, is particularly prone to deadly flash floods.

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Comments 1 to 4:

  1. I live in Southeast Arizona, at the edge of an expanding drought area affecting the entire Southwest. I have been trying to understand how global warming might make this better or worse. It could go either way - more rain because the atmosphere holds more water, or less because climate change is always bad. Are there any reliable predictions, based on climate models or other scientific reasoning?

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  2. The 4th National Climate Assessment (2018) is located here.  It is a good start and is easy to read.  They have a Southwest section.  Googling climate models Arizona also gets several useful hits.  The 5th assessment is due next year.

    The first rule of thumb is wet places will get wetter and dry places will get dryer.  In addition, when rain arrives more will come in big days with longer dry periods in between.  The US Southwest is expected to get dryer.  When the land drys out the temperatures go up since evaporating water cools the ground.

    Water from the Colorado river was allocated during a particularly wet period.  The future flow is expected to be a lot lower than it was in the past.

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  3. macquigg:

    "Atmosphere holds more water" is too simplistic to evaluate water cycle changes. It's true that warmer air hold more water vapour, which is likely to lead to increased evaporation, but that also means that somewhere, at some time, there will be more precipitation, too. Globally, evaporation = precipitation on any reasonably long time scale (months), and the question becomes one of "how does the local balance change?".

    Most land areas receive more precipitation than they lose in evaporation. Oceans are the opposite. Proof? Rivers draining from land to ocean. A lot of global variations in vegetation are explained by climate classifications that include some sort of water balance considerations (precipitation minus evaporation). The classic is the Koppen system.

    Soil moisture for agriculture can decrease even if local precipitation increases - if local evaporation increases even more. So "more precipitation" does not necessarily mean "wetter" from a soil perspective. And for agriculture without irrigation, when rain falls is critical. As the old story goes, farmers always complain about rain. Too much; not enough; not at the right time.

    For municipal uses, storage can help with seasonal and annual variability, but it can't make up for long-term expectations that want to use more water than is available from the long-term average.

    Very local predictions from global climate models are hard to do, but Michael Sweet has pointed you to some possible sources of information.

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  4. I was just looking at the very beautiful 'live' GPM model by NASA showing where precipitation is most likely to occur on earth.

    It seems to me that somewhere on the planet potentially record rainfall arrives every day.

    If there is no rain guage at that location to measure it's accumulation then sadly it is not entered into 'record books'.

    And it seems just as likely to me that this has always been the case.

    If you have no instrumentation present then the record level cannot be officially observed, no matter how extreme the new record is, or, has been in the past.

    But, regardless of that the tenacity of Galveston residents is something to be admired. The worst weather catastrophe in US history took place during flooding at Galveston in September 1900, killing 8000, people.

    The geographical location of Galveston is plainly a key issue. Storms last year, storms in 2017,  many storms and floods since 1900, seem to point to one thing - If you build a city on a low level island by the sea, in a storm prone area, then you need to be thankful for the subsidised flood insurance you get, as a result of the area being a well known heightened flood risk zone.

    I was talking to my friend in New York a couple of days ago about this, he just said, "well, it's Galveston, what do they expect". Harsh, but probably fair

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    Moderator Response:

    [BL] Throwing around statements like "it seems",  "potentially", "if there is no",  "it seems just as likely", "If you have no instrumentation present", etc. is just adding noise.

    You went through this sort of behaviour on other threads. You are making an argument from incredulity.

    Your misguided attempts to look at single events in isolation is as worthless here as it was on the UK temperature threads. Your statements prove nothing.

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