One of the emerging patterns that I see again and again as the volunteers and I survey the USHCN climate stations of record around the USA is that many of them have been relegated to back lots with an “out of sight, out of mind” attitude. At California Polytechnic Institute, San Luis Obispo, that attitude seems obvious.
Here we have a USHCN station in the middle of a junk pile. Old storage crates and containers, a rusty metal trailer, and a disabled Winnebago. Most curiously, one piece of junk, a discarded solar mirror, has the potential for heating up the thermometer more than a few degrees under certain conditions. It’s hard to believe, but this is exactly how I found the site.
This was my second attempt at surveying this site. In my first attempt, I found three other weather stations, all on campus building rooftops, and one of my readers said he spotted the “official station” in grass plot near a large parking lot. It turned out to be none of those. This station was tucked away behind the maintenance buildings.
Note how the solar mirror is pointed right at the shelter, under some sun angles, I’d wager that this reflects sunlight directly on the shelter. At other times, some localized heating of the ground and objects near the shelter could also occur, heating the air nearby. Here is another view:
In addition, the Stevensen Screen is wind sheltered on all sides, and a pool chemical test facility was recently constructed about 90 feet south, which adds humidity to the air, possibly increasing Tmin at night.
And, if that isn’t enough, the Stevenson Screen is at the crest of a small hill with acres of ashpalt and vehicles just below:
Given these many microsite biases, it is not at all surprising to see a sharp upwards temperature trend for this location.
The Cal Poly campus, like many, has seen a lot of building going on. In the last 5 years, two new buildings have been constructed just south of the station, and there have been other land use changes.
It seems a far less than ideal place to measure long term temperature trends. The complete station survey with additional photos is available on my surfacestations.org image server.