One of the really cool things about Tucson is how much climate and biological diversity one can experience within an hour or two’s drive from the city.
Most everyone is aware we are in the Sonoran Desert. The Sonoran is a unique desert in that it is subtropical, meaning there isn’t a lot of below freezing temperatures for very long. We also have two rainy seasons. The combination of not much cold and two rainy seasons creates an amazing diversity of plant species.
If you travel south or east, you will notice that the diversity of the plant life drops dramatically once you are south of Green Valley or out towards Benson. The reason for that is the elevation is higher and consequently it gets colder. Once you cross the line where below freezing temperatures are more common and last for hours, the Saguaro (for example) vanish.
The ironwood tree, which one finds mostly north and west of Tucson, is a very good indicator of it not getting really cold. Ironwood trees are especially sensitive to any amount of freezing weather, so there are none of them south and east of Tucson. Wherever ironwood trees grow, citrus trees will probably survive. That’s why there originally were orange groves on Orange Grove Road, because that area originally had ironwood trees and folks used that information to plant citrus groves.
As you go father west out beyond Gila Bend you’ll notice the variety of plant life in the desert decreases dramatically. That’s because the summer monsoon doesn’t reach farther west enough to add the extra rainfall we get here. Cold is not the limit to species diversity…aridity is.
Rainfall in the area varies by elevation. The higher the countryside, the more rain it gets. On the top of Mount Lemmon it can get 20 or 30 inches of rain and snow in a year, whereas the valley floor only gets 10 or 12 inches. Down Santa Cruz County way, where you start getting close to 4,000 feet near the border, they get 14 to 16 inches of rain each year.
Driving up from the valley floor to the top of Mount Lemmon is a journey through many climate zones all the way from desert to alpine. It is like going from here to Canada in an hour.
On a typical summer day, it seems like it is raining everywhere but at your house. This was once called the “rain encirclement syndrome” and is in fact true. Storms form over the mountains and drop their rain there, and don’t make it to the valley floor. That is also why the official rainfall measurement taken at the Tucson International Airport is almost always lower than most of the area, because most of Tucson is closer to the Catalina and Rincon mountains. The closer you are to the mountains, the more rain you will experience.
Once you get near 4,000 feet the environment really changes, from cactus studded desert to grasslands and oak trees. The drive down to Sonoita takes one from the Sonoran Desert in Tucson into rolling grasslands and oaks. You can also experience that difference driving down Mission Road behind Green Valley and then going up McGee Ranch Road which runs to the base of the Sierrita Mountains, or drive over to Oracle.
An interesting aspect of Tucson is you can actually choose what sort of climate and environment you want to live in. If you want more rain, cooler temperatures, and more trees, then live close to 4,000 feet. If you really like the desert, then live north and west of Tucson below 2,000 feet. There is actually over 2000 feet of elevation difference around the city before you even get into the mountains themselves. The whole urban area tilts downward from the southeast to the northwest.
It is an interesting tradeoff …the longer you are willing to commute to work, the greater the difference in climate options you have at your home. Thus you can live amidst oak trees and commute to the Sonoran Desert to work if you don’t mind a 1 hour drive.
There are also a lot of what are called “micro climates” around the area. For example, cold air drains off the mountains and down into the Tanque Verde, Sabino, Canada del Oro and Santa Cruz valleys. There can sometimes be easily 10 degree colder temps in the river bottom areas than on the surrounding hillsides on winter mornings.
Picking which plants to landscape your home with is actually hard in Tucson because something that will grow in one area of town will not in another. I use the basic rule that if the nursery is in the same microclimate as my home and the plants have survived the winter there, they will work at home. A really helpful thing to do if you are into gardening and landscaping is have a rain gauge and temp gauge so you can track what is actually going on in your yard.
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