Ag Weather Forum

Central Europe is trying to recover from heavy, record rainfall that fell in mid-September due to a large storm system named Boris. The USDA Weekly Weather and Crop Bulletin Sept. 17, 2024, noted that southwestern Poland had from 150-200 millimeters (mm) of rain or 6 to 8 inches. Other totals were as high or higher. The Czech Republic had rainfall totals reportedly as high as 463 mm or 18.2 inches; Austria had up to 371 mm or 14.6 inches of rain; Slovenia received 286 mm or 11.44 inches; Croatia had 257 mm or 10.28 inches; western Slovakia had 242 mm or 9.68 inches; and northeastern Italy had 164 mm or 6.56 inches of rain.

"There were widespread reports of flooding and damage to infrastructure along with numerous fatalities," the USDA bulletin said.

The tremendous rains from Boris in Europe are not the only occurrences of monster rainfall in September 2024. Writing in the Yale Climate Connections, atmospheric scientists Bob Henson and Jeff Masters note that unusually heavy rain in Africa drove close to 1 million people from their homes and caused more than 1,000 deaths. Typhoon Yagi struck the Philippines, Vietnam and interior Southeast Asia, producing floods and mudslides causing more than 500 deaths along with over $13 billion in damages. Storm Boris, of course, has caused billions in damage and forced thousands to evacuate flooded towns and cities in Central Europe. The U.S., too, has seen heavy flooding rains in the Gulf Coast and Carolina coast this month.

Storms with heavy rain are part of the weather cycle. However, atmospheric research points to how climate change due to greenhouse gas emissions is increasing the moisture content for storms to work with, resulting in rainfall totals that were not thought about a generation ago.

The NOAA National Centers for Environmental Information (NCEI) Global Climate Assessment for August 2024 notes that August was the 15th consecutive month of record-setting global temperatures -- records date back to 1850. Calendar year 2024 is on track to be the warmest year on record. And one of the features of a warming climate is more atmospheric moisture.

"Warmer global temperatures allow more water to evaporate from oceans and intensify rainfall, even as they also suck moisture from parched landscapes where it's not raining -- the 'wet get wetter, dry get drier' paradox," Bob Henson and Jeff Masters note in the Yale Climate Connections. Henson and Masters also emphasize the amount of precipitable water in the atmosphere in August was a record high for the month, along with being the 14th month in a row of record-high atmospheric moisture for the month. This analysis dates back to 1940. Precipitable water is the amount of water vapor in an imaginary column of air over a given point.

Another warmer-atmosphere feature that may have supported the flooding rains is a stalling of the progression of upper air ridges and troughs and a resulting "stuck" weather pattern. This feature is called quasi-resonant amplification (QRA) and is the focus of research going back more than 10 years. It may be an important factor in prolonged summer weather extremes across the Northern Hemisphere, according to Henson and Masters. A research paper published in 2018 concludes that these events could become up to 50% more common this century because of the impact of climate change.

The analysis group World Weather Attribution will release a report this week on its research showing to what degree climate change may have affected Storm Boris in the flooding rain across Central Europe.

The full Yale Climate Connections article by Bob Henson and Jeff Masters is available here: Epic floods are wreaking havoc from Africa to Asia to Europe » Yale Climate Connections

The 2018 report on Quasi-Resonant Amplification (QRA) is available here: Projected changes in persistent extreme summer weather events: The role of quasi-resonant amplification | Science Advances

Bryce Anderson can be reached at Bryce.Anderson@dtn.com

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