May 25 2007
Precipitation and Temperature Trends in Tucson, Arizona
Yesterday I posted a graph of average daily temperature in Tucson, Arizona for the last 60 years. The post for today will be similar. I’ve taken the same data, and smoothed it so that the long-term trends are more visible. In the following 2 graphs the temperature (below) is in degrees Fahrenheit, and the precipitation (bottom) is in inches.
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I filtered frequencies that occured at 2 years or less. This allows us to see some interesting patterns. As I pointed out yesterday, since a temperature minimum at around 1965, the Tucson area has been heating up. What I didn’t show you yesterday is the precipitation data taken from the same NCDC site. (Note: the 2-year filter will tend to accentuate the patterns that have a period slightly greater than 2 years. Hence, the apparent di-yearly cycle.) The apparent cutoff of temperature data at 2006 is an artifact of the axis. Data goes through May 1, 2007.
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The precipitation data unfortunately shows the opposite trend; Tucson has been receiving less rain since the mid-70s. The precipitation data only goes back to 1975 because that’s all I could find on the NCDC site. It is clear that since the temperatures have risen, precipitation has decreased. What is not clear is if this is a natural process or not. The IPCC 2007, and several papers since, have stated that the Southwest United States will experience less annual rainfall because of global warming; others disagree.
In other news, I came across this the other day - The Temperature is Rising in Tucson (subscription required). It frequently cites The skeptical environmentalist by Bjørn Lomborg, so I’d take it as a humorous piece.
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One Response to “Precipitation and Temperature Trends in Tucson, Arizona”
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How would the growth of Tucson over time affect this? In the last 30 years, metropolitan Tucson has more than doubled in population, buildings, roads, etc.
[Response: The growth of Tucson would have a large effect on the temperature trends. If I recall correctly, about 75% of the observed heating in the area is of an urban heat island effect. The rest is either natural or global warming or both. (I forget the source for this. But I can search if you'd like to read it.) Precipitation is more problematic. It probably has changed during the last 30 years due to the regional changes in weather patterns. But this change is surely below the detection limit right now.]