From Dr. Spencer's Global Warming Blog
Author: Dr. Roy W. Spencer
This is the first in a series of articles on the urban heat island (UHI) impacts of daily record high temperatures. My previous UHI work has always used the GHCN monthly average station data of “Tavg” (the average of daily maximum values) [Tmax] and minimum value [Tmin] temperature). Therefore, I will move from Tavg to Tmax (since record high temperatures are of great interest), and daily values rather than monthly values (although I will sometimes include monthly results to provide context).
This post is mostly a teaser. Finally, I will describe a new dimension of my nascent UHI work.
The poster child for U.S. warming in 2024: Palm Springs, California
I searched on Google for record high temperatures in the United States in 2024, and it seemed Palm Springs, California, was a place to start.
The name of this place is like “Palm Springs” which sounds like a great place to rest under the palm trees and enjoy the cool refreshing spring water all around. Instead, the site is mostly a desert, where a spring in the original city center gushes out 26 gallons of hot water per minute. “Palms” do exist… they are “desert palms” that grow naturally in clusters where groundwater from mountain snowmelt seeps in through cracks connected to the San Andreas Fault.
Like all metropolitan areas in the United States, Palm Springs has experienced rapid population growth over the past 100 years. Even in the last 50 years, the population has almost doubled. Natural desert surfaces have been replaced by pavements and roofs, which are warmer than the original desert soil, while the “impermeable” nature of artificial surfaces (with little air content) means heat is conducted downwards, causing excess heat to be stored for long periods of time , the average temperature is higher. More on “impermeable” surfaces later…
Palm Springs Airport Weather Observatory
The Google Earth image below shows the current location of the Palm Springs Airport ASOS (Automated Surface Observing System) official site, which recorded an all-time high temperature of 124 degrees Celsius. F on July 5 this year.
Interestingly, the ASOS weather instrument site selection guidelines favor natural surface placement, but since most weather stations are located at airports (and they primarily support aviation weather needs, not climate monitoring needs), the “natural” location is usually right on Next to runways, airplanes and paved roads.
The next Google Earth image is zoomed out to show the larger Palm Springs area, with the ASOS website in the center (click on the image to zoom, then click to zoom further).
Record July temperatures and urbanization
It only makes sense that people want to know the temperature where they live, and most Americans live in cities or suburbs. However, the temperatures they experience are probably, without exception, higher than before people moved there and started building roads, buildings and airports.
But for those paying attention to the global warming narrative, what is misleading is that the record high temperatures reported in these locations almost always mention climate change as a cause, But they have no way of knowing the extent to which urbanization is driving record heat. (Remember, even without global warming, heat records would continue to be broken as urbanization increases).
As mentioned above, on July 5, 2024, Palm Springs broke the all-time record for the highest temperature, reaching 124 degrees Celsius. F. There are also 26 daily GHCN monitoring stations within 40 miles of Palm Springs, which vary in their levels of urbanization but, more importantly, in altitude. If we plot the high temperatures reported by these sites on July 5th as a function of site elevation, we find that Palm Springs is an “outlier,” being 5 degrees warmer than expected based on the expected temperature corrected for its elevation (dashed line regression) .
Now, keep in mind that many, if not most, of the 26 surrounding stations have their own level of urbanization, which makes them hotter than they would be without sidewalks and roofs. So, that 5 degrees. F Excess may be underestimating the impact of urban warming on Palm Springs' record heat. Palm Springs was incorporated in 1938, and much of the area's population growth occurred after World War II.
If you're curious about how the previous graph shows the average temperatures for all July, take a look here:
In July, the average temperature in Palm Springs is 3 degrees. F is warmer than surrounding stations (after adjusting for altitude effects, and remembering that most *other* stations may have their own urbanization levels).
Clearly, Palm Springs is suffering from a false warming effect of the airport and surrounding urbanization that did not exist 100 years ago. But how much?
Impermeable surface materials as urban alternatives
This blog post is a prelude to a new project we are embarking on, where we will compare daily (and monthly) temperatures based on Landsat data with the relatively new USGS dataset covering 1985 to 2023 of annual impermeable surface coverage. I had previously tried the “Built Up” dataset based on Landsat data, but that turned out to be just buildings. I think the “Impervious Surfaces” data set has the most direct physical connection to what causes UHI warming: roads, parking lots, rooftops, etc. My work on population density (which, we hope, is close to being accepted for publication).
Relevant
