More on the Arizona Monsoon and Urban Heat Island

While unemployed. I am attempting knowledge retention through reading the books that once decorated my office shelf. Reading science books probably won’t win me the ladies, but it at least feels more productive than watching television.

A few years ago I picked up a book called Rangeland Hydrology at a used book store. The book is published by the Society for Range Management, and I have the second edition from 1981 (see the end of this post for a complete reference). Early in the first chapter, this passage caught my attention:

“The local type thunderstorms often lead to statements from disappointed ranchers that it seems to rain everywhere but on their ranches. Exclamations such as ‘We were completely surrounded by storms but somehow they all veered around us and we didn’t get a drop all afternoon.'”

Holy cow! That is exactly the “evidence” given by people who believe that a growing Phoenix has diminished monsoon rains from the time of the “good old days”. Curiously, this book was published in 1981, during the period of the “good old days”, and is describing rural areas where urban heat islands don’t exist! Interestingly, the authors found this observation common enough to mention.

To what do the authors of this book attribute this phenomenon? The authors conclude this common observation has to do with the short-lived nature of the storms, the small areal extent of the rainfall, and the perspective of the observer. The book relays its reasoning as clever and simple mathematical experiment.

I like this kind of science. Simple solutions to age-old questions using nothing more than careful reasoning and simple math.


Branson, F.A, Gifford, G.F, Renard, K.G., and Hadley, R.F. (1981). Rangeland Hydrology. Dubuque: Kendall/Hunt publishing.

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