Is it Getting More Humid In the US?

I conducted an analysis of humidity trends for 26 major U.S. cities from 1970 to 2023. This analysis focused on the 1% dew point, which represents the outdoor dew point exceeded during the most humid 1% of hours in a year. In other words, when a place gets humid, how humid does it get?

For each city, I applied a Mann-Kendall trend test to detect statistically significant trends in humidity, and used the Theil-Sen slope to estimate the rate of change in dew point over time. The results were visualized in interactive plots, showing the year-by-year 1% dew point values along with trend lines and the overall change in dew point for each city.

Results: Out of the 26 cities analyzed, 18 showed statistically significant increases in the 1% dew point. The remaining 8 cities, while not showing statistically significant increases, still exhibited nominal increases in the 1% dew point. So basically, yes, it is definitely getting more humid. This result isn’t a surprise given that we know the climate is warming. As it warms, water evaporates more readily, and humidity increases.

How did I make these charts? First, I gathered and organized a massive amount of data from various sources, then used Python to analyze the data, then Folium to create interactive maps.

Specifically, this map uses hourly dew point data from Open Meteo.

Note: this map uses dew point instead of relative humidity. Relative humidity is an incredibly misleading way to assess the amount of moisture in the air - if you’d like to hear why, check out my dehumidification video on Youtube. Let’s quickly review the dew point scale. 30 Fahrenheit is very dry, 40 is dry, 50 is comfortable, 60 is a little bit humid, 70 is oppressively humid, 80+ is inhumane.

Note: To confirm my results, I conducted linear regression, moving averages, and bootstrap resampling in addition to the Mann-Kendall trend test and Theil-Sen slope. Same results.