A few folks have mentioned to me over the years that they thought we haven’t been getting as many frosts and freezes as in the past, that mosquitos were worse than in years past, and that it seems more humid than it used to be.
Of course the reaction could be to say “Global Warming”. But you’d be surprised (as I was) to learn that there may be another reason. Irrigation. Rice Fields, cotton fields, nut orchards, and other agricultural enterprises have grown (pardon the pun) dramatically in the San Joaquin and Sacramento Valley in the last century. A University of Alabama study found that Irrigation was likely the cause of increased overnight temperatures.
Intrigued, I decided to lookup and plot the minimum temperature data for Chico University Farm, which is the station of record for climate here to see if it showed the same trend. It did. Here is the results of data from 1900-2000:
And to be consistent, I also plotted the maximum temps too, which was surprising:
And even more surprising was the Mean Annual Temperature:
If anybody wants to check my data, I’ll gladly make it available. Here’s the article in its entirety:
Irrigation most likely to blame for Central California warming From: University of Alabama, Hunstville
http://www.uah.edu/News/newsread.php?newsID=293
The same irrigation that turned California’s Central Valley from desert into productive farmland is probably also to blame for summer nights there getting noticeably warmer.
Irrigation has turned much of the San Joaquin Valley’s dry, light-colored soil dark and damp, says Dr. John Christy, director of the Earth System Science Center at The University of Alabama in Huntsville (UAH). While the valley’s light, dry desert ground couldn’t absorb or hold much heat energy, the dark, damp irrigated fields “can absorb heat like a sponge in the day and then, at night, release that heat into the atmosphere.”
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