Paul Gross: High heat index days becoming more frequent

Study researched 239 cities nationwide, including 8 in Michigan

Climate Central's study researched 239 cities nationwide, including eight in Michigan. (WDIV)
Climate Central's study researched 239 cities nationwide, including eight in Michigan. (WDIV)

DETROIT – New research conducted by Climate Central and released this week shows that high heat index days here in Detroit are increasing.  
We’ve talked about the heat index a lot this summer, and you probably know what it is:  When it’s hot outside, higher humidity makes it feel even hotter because, when it’s humid, less sweat evaporates from our skin and that reduces our body’s ability to cool itself...hence, we feel hotter.  
Climate Central’s study researched 239 cities nationwide, including eight in Michigan, to see if heat index days of 90 degrees or greater are increasing over the past 40 years due to the overall warming of our climate.  

And the study found that 198 of those 239 cities experienced an increase in the annual average number of days with heat index temperatures of 90 degrees or hotter.  
So where are those days increasing the most?  Down south...where they need it the least.  McAllen, Texas tops the list with an increase of 31.6 annual 90 degree heat index days since 1979.  Well-known cities in the south also on the top 10 list include New Orleans (23.6 days), Miami (23.0 days), and Savannah (22.8 days).
Here are the stats for the eight cities in Michigan:

One thing that you probably noticed on the above charts is that the trend decreases the farther north you head in the state due to rising temperatures occurring more predominantly in winter than in summer.  But here in the Detroit area, the trend is unmistakably upward.  

About 15 years ago, I interviewed a climate scientist who specialized in regional climate change.  

At that time, he told me that as a result of the warming climate, in 75 years, a southeast Michigan summer will feel like a southwest Missouri summer does today.  More 90 plus degree heat index days certainly would be a part of that.
High heat and heat indices stress humans, animals and plants.  So this report is not good news for Metro Detroit.

About the Author:

Local 4 meteorologist Paul Gross was born in Detroit and has spent his entire life and career right here in southeast Michigan. Paul has researched, written and produced eight half-hour documentaries for WDIV, as well as many science, historical and environmental stories.