Sacramento and Urban Heat Island Distorts the Facts

Russ Steele

While I was doing some fact checking on the California Energy Commission and the Natural Resources Agency Our Changing Climate 2012 Third Assessment Report that made some claims about more 105 degree days in Sacramento, I plotted the number of extreme heat days from 1878 to 2010.

Just for fun, I did a regression analysis on the numbers and was surprised by the result

Doing some online research, I found a National Weather Service Document Climate of Sacramento, Updated 2010.  In this document we learn that the temperature sensor site has been moved around a bit, but is now is at the Sacramento Water Plant.

On September 28, 1964, the observation site was returned to the post office building at 9th and I streets. On April 1, 1999, the sensors were moved to the Sacramento Water Treatment Plant, east of California State University-Sacramento. Temperature and precipitation data has been transmitted from these locations to the National Weather Service Office since September 28, 1964.

This plant is in a build up area with a lot of concrete according to Google Earth, which could be contributing to a potential heat island.  I decided to look at other nearby sensors and see if they were seeing an increase in extreme heat days. I chose Lodi and Willows to bracket Sacramento.  These stations with records going back to 1931 did not show the same increase in extreme temperatures. I also replotted the Sacramento data from 1931 for an apples to apples comparison.

It appears that we are seeing some Urban Heat Island effect in the Sacramento extreme temperatures. This data also calls in to question the assertion in the Our Changing Climate report that extreme days are increasing, it appears that they are in fact decreasing. Another reason to question the validity of the Third Assessment.


About Russ Steele
Freelance writer and climate change blogger. Russ spent twenty years in the Air Force as a navigator specializing in electronics warfare and digital systems. After his service he was employed for sixteen years as concept developer for TRW, an aerospace and automotive company, and then was CEO of a non-profit Internet provider for 18 months. Russ's articles have appeared in Comstock's Business, Capitol Journal, Trailer Life, Monitoring Times, and Idaho Magazine.

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