Humidity, Heavy Rains, and the Toll of a Warming Climate



I sat on the front porch a few weeks ago and watched as Mother Nature did her best to drown our part of southeast Michigan. On that Saturday morning, what was supposed to have been a quick-hitting shower turned into a series of heavy downpours over an eight-hour period.

By lunchtime on that Saturday, we had nearly three inches of rain to add to the nearly two inches we had had the day before. In less than 24 hours, a total of inches of rainfall.

Highway and urban flooding was prevalent and the swollen rivers persisted for nearly a week. Of course, getting five inches of rain in a day is not unknown. Many of us remember that fateful August a few years ago in which parts of Oakland and Wayne County got six inches of rain in less than four hours, causing highway closures and thousands of flooded basements and yards.

But the point isn’t that we’re getting unusually heavy rains lately, but that we’re getting so many of them.

I am sure growing up in Saginaw in the 60s and 70s we had our fair share of heavy rains, but I don’t remember the TV weatherman telling us about two, three, four-inch rainfalls. I am sure that part of the reason is that meteorological technology at the time, for what it was, couldn’t predict rainfall amounts to the degree that it can today. But there is another mechanism at work that can explain just why we are getting so many ridiculously heavy rainfalls that sound like snowfall when predicted in 3”, 4”, and even 5”-6” amounts.

In a word, humidity.

Humidity is simply the amount of water vapor in the air, and all of us intuitively understand that humidity in the summer is much higher than winter because we get a lot more wind and weather systems coming up out of the Gulf region. The air above the Gulf of Mexico and the states immediately bordering it is much warmer and can ‘hold’ a lot more moisture than colder air to the north. But when that moist, warm air runs into cooler air in the north this time of year, condensation occurs, and those resulting clouds can drench any locale with an insane amount of rain in a relatively short period of time.

Sometimes, a long strand of storms will pound the same area for a prolonged period of time. This is called ‘training’ and can deliver a frightening amount of rain in a relatively narrow strip of land, leaving nearby areas dry.

But just why is humidity on the increase, and with it, more frequent heavy rainfall? Global warming.

As the atmosphere gets warmer, so do the oceans, and as the oceans get warmer, and the air above it, there is more evaporation, which leads to higher humidity and subsequently, more frequent and heavier rainfall. And with ocean levels going up, the oceans are also getting incrementally bigger with more surface area, leading to more evaporation and higher humidity, and ultimately, more rain.

Climatologists, who have studied weather for extended periods of times covering many decades and centuries, notice the increase in precipitation. Areas that rarely used to get heavy, frequent rains, are now seeing more torrential downpours, replete with flash floods, and loss of life and property.

Insurance companies and actuaries have noticed the rapid increase in claims due to storm and rain damage, and let me be the first to point out, they are not motivated by politics to embrace or denounce science. They pore over their data, notice trends, make predictions, and then plan accordingly.

So, if you are one of those who refuse to believe science, then at least trust your insurance agent. They see the results of what scientists have been cautioning about for decades.