Are Your Wiper Blades Moving Fast Enough For Sunday’s Rainstorms?

Oct 18, 2024

Intense rainstorm in Georgia

Much of the content that I write about comes from the convergence of routine life and being an atmospheric scientist. Yesterday, my family and I were driving home from a college recruiting trip. We encountered very intense rainfall as we entered Gwinnett County, a suburb just northeast of Atlanta, Georgia. The wiper blades were at full speed and could not keep up with the intensity of the rainfall. I said to my wife, “The current generation of wiper blade settings are not ready for the climate change-juiced rainstorms of today.” She pulled out her phone and snapped the picture above because she probably knew a Forbes article was coming. Here’s the science behind my statement.

Weather radar depicting intense rainstorms in the Atlanta metropolitan area on August 17th, 2024.

While my observations about wiper blade rates are somewhat anecdotal, here’s what I do know. I had a difficult time seeing the road in that rainstorm yesterday, and the wiper blades on that car were recently installed. My wife also happened to snap a picture of my phone showing the weather radar (picture above). Yes, it’s true. I am a “weather geek,” so it is not uncommon for my phone to be on the radar in these situations. The blue circle indicates the position of our car within that afternoon thunderstorm.

Here’s also what’s not anecdotal. Scientific studies consistently show that rainfall intensities are increasing in the U.S. Rainfall intensity or rate is essentially a measure of how hard it rains. The 2023 U.S. National Climate Assessment report notes, “Since the 1950s, there has been an upward trend in heavy precipitation across the contiguous US ... increase is driven largely by more frequent precipitation extremes, with relatively smaller changes in their intensity.” The Northeast and Midwest have seen the largest increases. Here in the Southeast, total precipitation in the heaviest 1% of days has increased by 37% from 1958 to 2021.

Trends in precipitation over the period 1958 to 2021.

Climate Central recently produced a Simple Hourly Rainfall Intensity Index characterized as the total annual rainfall divide by total annual hours with rainfall. They analyzed 150 U.S. weather stations spanning the period of 1970-2022. They found that 91% of the weather stations had an increase in hourly rainfall intensity over the past 50 years. The average increase was around 13%.

The Climate Central report also warned, “The increase in hourly heavy rainfall intensity is widespread and that the risks posed by short bursts of extreme rainfall are relevant for both wet and dry locations.” They also noted that findings are consistent with the latest data from the Intergovernmental Panel on Climate Change, which also indicates that precipitation extremes are likely on the rise in all regions, even dry ones.

Warming climate affects the water cycle in many ways.

If you have noticed that heavy rainstorms are more intense than during your childhood, you are not imagining things. Scientific studies support your observations. This is an important point to understand as climate change continues to modify the nature of precipitation events. People often get stuck on the question, “Am I getting more total rainfall where I live?” I usually answer, “Perhaps or not, but the literature is pretty clear that more rain is falling in a given duration during the most intense storms.” These days you may see terms like rainbursts or rain “bombs” which gives more emphasis than “downpour.” When the remnants of Hurricane Ida (2021) moved into the Northeast, it was able to dump 3.15 inches of rainfall on Central Park in one hour. That rate broke the record for wettest hour at that location.

By the way, a relationship that is nearly two centuries old explains much of what is going on with rainfall and climate change. Writing in a Proceedings of the National Academy of Sciences blog, David Adam said, “The relationship is now known as the Clausius–Clapeyron equation.... The equation shows how warmer air can hold more moisture, which is crucial to forecast the increased strength of storms and the higher intensity of rainfall.” In the same blog, Peter Stott, a climate scientist at the U.K. Met Office, told Adam, “An exponential curve, of course, goes up more steeply the further up you get. So quite quickly as temperature increases, you get into large numbers for additional rainfall.”

Natural and urban water cycle processes.

Such intense rainfall also leads to flooding, particularly in urbanized spaces and along roadways. Two factors, beyond rainfall are, are important in the flood equation today. Impervious surfaces like parking lots and roadways affect the water cycle. They cause less infiltration of rainwater into the soil and increase the rate of runoff into streams, creeks, and rivers. Lara Milligan, a Natural Resources Agent for UF/IFAS Extension Pinellas County, wrote an outstanding blog illustrating these processes.

Both changes lead to flooding. My University of Georgia colleague Brian Bledsoe, director of the Institute for Resilient Infrastructure Systems, has repeatedly pointed out that much of the nation’s stormwater design is hampered by something called “stationarity.” In other words, the engineered infrastructure was built assuming rainstorms of 1970 would look like the rainstorms of 2024 and beyond. They don’t. My work with Bledsoe and other colleagues at IRIS is using science and engineering findings to reimagine how to plan or design urban spaces to account for the evolving weather and climate.

LITHIA SPRINGS, GA - SEPTEMBER 22: In this satellite image, wide spread flooding is shown September ... [+] 22, 2009 in Lithia Springs, Georgia, just west of downtown Atlanta. Gov. Sonny Perdue has asked that a federal state of emergency be declared for the area. (Photo by DigitalGlobe via Getty Images)

Interestingly, there is research showing that modern automated car systems may be viable weather observations. A 2019 press release from the University of Michigan said, “Utilizing a test fleet in the city of Ann Arbor, engineers tracked when wipers were being used and matched it with video from onboard cameras to document rainfall.... tracking windshield wiper activity can provide faster, more accurate rainfall data than radar and rain gauge systems we currently have in place.” Cars represent a robust source of weather information so this research is promising, especially given the density of automobiles and gaps in radar or rain gauge coverage.

However, these studies did not address whether the fast wiper blade settings are keeping pace with higher rainfall rates. Ironically, several car enthusiast blogs or websites have chatter about the performance of their wipers in downpours and what to do when they are not keeping. Suggested solutions include:

Blade rates vary by car manufacturer and the embedded wiper motors. According to the 2024 Sontian Motor Wiper Motor Guide, “The wiper motor rpm is usually for 45 rpm for normal speed and around 65 rpm when on the fast speed settings.” I suppose the ultimate question is whether a faster rate is now required for contemporary rainstorms. Cities are now reconsidering stormwater design as rainstorms change. Perhaps this article is a “flashing signal” to the car industry and another example of the “So what?” when people inquire about how climate change affects their lives.

Woodmere, N.Y.: Motorists driving on Peninsula Blvd. negotiate their way through the heavy rain and ... [+] flooding in Woodmere, New York on September 29, 2023. (Photo by J. Conrad Williams Jr./Newsday RM via Getty Images)