Russ Steele
I wrote here about and an internal U.S. Forest Service report that was circulating on how climate change is effecting the Tahoe National Forest and neighboring El Dorado National Forest: A summary of current trends and probable future trends in climate and climate-driven processes in the Eldorado and Tahoe National Forests and the neighboring Sierra Nevada. This report was written by Chris Mallek, Department of Plant Sciences; University of California-Davis and Hugh Safford, Regional Ecologist, USDA Forest Service, Pacific Southwest Region. A copy of the report is here.
As I wrote in my previous post, the climate data in the report was derived from four weather stations with long-term meteorological records from the general area of the El Dorado and Tahoe National Forests. The stations were, Nevada City, Placerville, Truckee and Lake Spaulding. This post will focus on the Placerville station which, as the report claims is evidence of pronounced global warming.
Since 1949, mean annual temperatures at Placerville have risen sharply by about 6.4° F, with corresponding increases in mean maxima and mean minima of 4.1° F and 8.4° F, respectively.
As we found out in our examination of the Nevada City station and the reported warming, there is more to the story than just capturing some data and then suggesting the warming is a result of human activity. Nevada City details here.
However, I think we can conclude that the Placerville warming is the result of human activity, as the weather station (COOP 046960), is located at the Pacific Gas and Electric Company Facility on on Missouri Flat Road in Placerville, CA. However, I am not so sure the warming is from human emissions of greenhouse gases. Here is a Google Earth Photo.
What strikes you about this facility and the weather station location? Right, a huge area of concrete (or black top) surrounds the station. During the day the concrete or blacktop heats up in the sun and at night gives back that heat to the local area, creating a night time heat island. This is not the ideal location for a weather station, which is supposed to be 100 feet from potential heat sources. This station is siting on top of a night time heater. I am assuming that since 1949 the facility has grown, adding more parking spaces and sun absorbing concrete, and the urban area surrounding the station has expaned over time. All which can boost the night time temperatures. I will be paying the site a visit to confirm these assumptions.
Here is a plot of the annual data:
I looked for a nearby site that was not co-located with a huge concrete parking lot. None of the local COOP Station had long enough records, or temperature measuring equipment. Next I looked, for a near by Remote Automate Weather Station (RAWS) which are operated by the Forest Service. I found Owens Camp station which is 31.5 miles due east of the Placerville COOP station. A station that is actually in the National Forest where the global warming was forecast to be taking place. The station has a long record for a RAWS Station from 1990 to 2010, with some missing months in 1995 and 1996.
Here is plot of the monthly data plot of this station, with a regression line:
It appears there is about 1.5 degrees of warming in the National Forest, with about .5 degree decline in the max and a 2 degree increase in the min temperatures over 20 years. Or about, 0.075 degrees per year. This is far from the “mean maxima and mean minima of 4.1° F and 8.4°” in the Forest Service report, with a average of 6.4 degrees or about 0.1067 degrees per year. I am estimating here, as there were a number of month with no data in 1995 and 1996.
If global warming is happening in the National Forest, why is there such a difference just 31.5 miles away? It is true the RAWS Station is located at 5,240 feet elevation, and the PG&E COOP station is at 1,850 feet elevation. The difference in altitude can account for the differences in temperatures, but not for the difference in warming trends. I am suggesting that one of the major factors is the location of the Placerville station over a huge concrete parking lot. This expanse of concrete and the urban growth around the area would create a heat island that influencing the growth in higher temperatures.
Follow up. I plan to be in Placerville in a few weeks and will be take some ground level pictures of the site and interview the PG&E staff to see if there is Service Yard growth history. This should provide some more insight into to the rapid increase in temperatures in Placerville. Stay tuned, I have two more stations of examine.
