NASA study sheds light on heat waves in Southern California

Driving into Los Angeles
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September 6, 2023 — As climate change intensifies, Southern California will face increasingly frequent and severe heat waves, warns a new study from NASA’s Jet Propulsion Laboratory (JPL). According to the scientists, focusing solely on air temperature does not capture the complete risk profile. Instead, they recommend that humidity should also be considered when issuing extreme heat warnings. The study points out that heat stress due to high wet-bulb temperatures—linked to human body cooling capabilities—can be worse in muggy conditions, even if air temperatures are cooler.

Heat Islands and Variable Impact Zones.

The study places particular emphasis on the Greater Los Angeles area as an “urban heat islandOpens in a new tab.,” where heat-trapping concrete and asphalt elevate temperatures compared to rural regions. The area is unique for its complex geography and population density, making it an important case study for heat wave impacts. The scientists used advanced modeling to simulate heat waves and found that different regions within the Greater L.A. area experience heat waves differently due to local climate and vegetation.

From Dry to Muggy Heat Waves.

Climate change has transformed the nature of heat waves in the region. While the 20th century saw mostly dry heat waves in L.A., humid events have been on the rise since 1950, partly due to warming sea surface temperatures. The researchers discovered that both coastal and inland areas are now experiencing increased nighttime heat stress during humid heat waves, a notable change particularly for valley regions which historically had drier nights.

The findings highlight the importance of considering microclimate variations when designing emergency plans and policies to deal with heat waves, now and in the future.


Since 1995, Deborah has owned and operated LegalTech LLC with a focus on water rights. Before moving to Arizona in 1986, she worked as a quality control analyst for Honeywell and in commercial real estate, both in Texas. She learned about Arizona's water rights from the late and great attorney Michael Brophy of Ryley, Carlock & Applewhite. Her side interests are writing (and reading), Wordpress programming and much more.

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Ivy Batriani
Ivy Batriani
September 9, 2023 4:47 pm
Growing up in both New Jersey and Phoenix, I can tell the difference in the air when the humidity creeps above 18%. When the temperature and the humidity are high, you can literally feel the weight of the air. It is heavy and stifling and can create respiratory chaos. Based on my own experiences, I too believe that humidity should also be considered when issuing extreme heat warnings.

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