Russ Steele
Feeling the Heat was published by Environment California a non-profit group a few weeks ago, claiming 2007 was the tenth warmest year on record and that the mountain west was experiencing above-average temperatures. Full report here: Download feeling_the_heat_ca.pdf One of the examples given for the high western temperatures was Reno Nevada with a average temperature of 55.3 degrees in 2007, four degrees higher than the 30 years average temperatures from 1971 to 2000. The EC report is concerned about the night time low temperatures rising higher than the 1971-2000 average, again citing Reno as an example, with an average minimum temperature of 40.7 degrees - more than five degrees higher than the 1971 to 2000 average.
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My interest in the report grew more intense, as I had been doing some research on UHI in Reno following Anthony Watts survey the Airport ASOS shown above. The Reno Airport is in the Historical Climatology Network and Anthony Watts Surface Station Survey data base. I decided to dig a little deeper into the data provided in the EC report which was funded by the The Pew Charitable Trusts and Energy Foundation. The report was written by Emily Figdor, who was recently recognized as a top global warming lobbyist by The Hill, a Capitol Hill newspaper.
Up front in the EC report the author dispatches the idea that UHI was having any influence on the climate change, citing studies by Easterling, PD Jones and Parker
In a 1997 study, by David Easterling of the National Climatic Data Center examined data from 5,400 weather stations, of which 1,300 were located in urban areas. He found that urban effects on globally averaged temperature data were “negligible” and did not exceed about 0.05°C over the period 1900-1990. These results confirm the conclusions of a similar 1990 study [PD Jones]. David Parker of the UK’s Hadley Centre also found that global temperatures have risen as much on windy nights (when the urban heat island effect is diminished) as on calm nights (when the effect is at its strongest). He concluded that “overall warming is not a consequence of urban development."
In earlier Internet research I had found a National Weather Service Technical Memoranda, CLIMATE OF RENO, NEVADA written by Brian F. O’Hara. He wrote that Reno had grown to surround the airport and temperatures have been influenced by the effects of the urban heat retained in urban concrete, brick and asphalt. O'Hare writes:
During the summer afternoon highs are often above 90° F, but at night the air mass can cool down into the 50s. In the last five or six years however, nighttime lows during July and early August sometimes do not make it below 65° F. As will be seen in the tables in the Temperature section below, this warming trend has been seen in summer high temperatures, but not to the extent that it is reflected in the nighttime temperatures.
These conditions maybe due to an urban heat island effect. Since the early 1940s the official observation site for Reno has been the airport. When the airport became the official observation site on September 1, 1942 the airport was a few miles southeast of town in a rural area. There was a noticeable cooling in the average temperatures during the 1940s from what had been seen during the 1930s when the observation site was downtown. Average temperatures have shown a gradual warming trend over the decades. This consistent warming may be due to the fact that the city of Reno has grown in area and now surrounds the airport. The weather observation site is now in an urban area, and thus the air mass (especially during summer) has a more difficult time cooling down at night.
O'Hara concludes:
Average temperatures then started a gradual warm-up, with impressive rises during the 1980s and 1990s (urban heat island effects). In a strongly developed heat island, the temperature in the urban area can be up to 10°F greater than it is in the surrounding rural areas (Oliver and Hidore, 2002).
I found this chart from the Nevada Bureau of Mines and Geology, Weather and Climate of the Reno-Carson City-Lake Tahoe Region report, again O'Hare was the main author.
Note how the annual temperature increased over time as Reno grew and then it dropped once the sensor was moved from downtown to the airport which was quite rural at the time. As Reno enveloped and surrounded the airport the temperatures continued to increase. Also, as the Reno Airport grew to handle a growing population the Airport increased the square yards of concrete and black top, which collects the daytime heat and releases it back at night.
Now that we have confirmed Reno has some UHI influences, could this be the only reason for higher temperatures. A HO-83 temperature and humidity sensor was installed at the Reno Airport in November of 1984, and upgraded to a full ASOS in September of 1995, according to the NCDC Station History. The HO-83 is know to have a warm bias between 0.5C to 0.7C. as shown here.
I cannot find any information that this sensor has been removed in the NCDC History File. You can find the details on HO-83 bias at Climate Audit and Watts Up With That.
It turns out that all the station temperatures in Feeling the Heat were taken from Airports, as you can see in this table of top ten highest temperature stations.
From the Methods section of the report:
We looked at data from 255 major weather stations. We generated this list of 255 stations from a list of “First Order” stations in the continental United States, obtained from Weather 2000,62 a meteorological consulting firm.
The "First Order" data was taken from National Climatic Data Center (NCDC) of the National Oceanic & Atmospheric Administration's DS-3210 data set. Which is automated ASOS data taken from civilian airports and military air bases. According to the data set description there is very little auditing done on the data, mostly by computer, to insure the data fits in an established template. It is considered more accurate that human recorded data according to NCDC.
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As you can see this the Reno Airport in now surrounded by dense urbanization, the main cause of UHI. I would say the increase in temperatures is human caused warming through urbanization, with very little caused by increases in greenhouse gases. The next step is to find an another near by station and compare the temperatures, are they rising also?
Last year, I found a Remote Automated Weather Station operated by the Forest Service at Desert Springs that is 11.28 miles due north of the Reno Airport, in a remote area well away from urban influences. The annual temperature in desert far from urban influence in 2007 was 52.54 F, which was 2.8 F below the Airport ASOS just eleven miles away. As you can see this site is quite remote.
Desert Springs, click for larger image.
Here is a plot from last year comparing the Desert Springs and Reno ASOS.
Digging even more, I discovered the National Weather Service Forecasting Center has a surface station that has been in operation since the mid 1990s. It is only 4.36 miles from the Reno Airport, to the north north west of the Airport at the head of a canyon. The NWSFO site was 1.4 degrees below the Airport ASOS. This site does have some urban influences, a nearby college and some concrete parking spaces. Here are two photo, first to show the location, the second the surface station.
NWAFO Station, high view,
NWSFO Surface Station
Here is a plot the average temperature comparing the Reno and NWAFO sites.
The temperatures track in parallel until 2003, and then come together in 2005, and then diverge over the 2006 and 2007 time periods. These sites are only a few miles apart, yet there is a one degree difference. I decided to look at the Airport ASOS min / max temperature plot, was the min rising faster than the max?
As you can see the plot shows an increase in night time minimum temperatures over the day time temperatures from about 1950, shortly after the sensor was moved to the Reno Airport, which would be an indicators of UHI influence, when the urbanization drives up the min as the concrete, blacktop and surrounding buildings gave up heat as the night air cooled.
I think, we can conclude that Reno's record temperatures are UHI related. As the temperature records move from a rural location, to a semi-rural location to the airport surrounded by urban development, they increase. Sensor site locations are shown in this Google Earth photo.
What have I missed? Reno's high temperatures are UHI related.
Next up is a look at Helena Montana. Are these high temperatures also UHI related?
