The Phoenix area is extremely hot. We average 110 days a year over 100 degrees, and it doesn’t cool off much at night. That heat is relentless.
In early July, just when I feel I can’t take it anymore, I will scream if I see another temperature reading of 116 on my car dash, and I swear I’m moving someplace cold before next summer, something changes. Our single-digit humidity begins to creep up to 30% or more.
It’s the first hint that the monsoon season is coming to the desert.
I grew up in the Midwest and was used to lightning and thunderstorms. But when I experienced my first monsoon storm in Arizona, I discovered just how awe-inspiring life in the desert can be.
Why does Phoenix have summer monsoons? Doesn’t it seems counter-intuitive to have the majority of the rainfall when the temperatures are the highest?
Those high pressure ridges are the product of global air circulation known as the Hadley Cell. The air at the equator heats and rises to the lower atmosphere, where it diverges, moving away from the equator, both north and south, until it cools and sinks around the 30th parallel in both hemispheres. At the surface level, the sinking air diverges again with some returning from the equator, completing the Hadley circulation.
The end result is that little or no moisture ever reaches the ground below this climatological high-pressure area. Thus, the horse latitudes produce arid climates in the areas below them. The Sahara, for example, is situated in a horse latitude. So is our own Sonoran desert.
But luckily for us, we get a reprieve.
On average, Arizona gets about half of its annual rainfall during the summer monsoon.
The wind shift and increase in moisture combine with the surface low pressure from the desert heat to produce storms in a cycle of “bursts” (heavy rainfall) and “breaks” (suddenly reduced rain).
Driving through a haboob can be terrifying. Drivers are instructed to pull off the road, turn their lights off, and wait until it has passed.
The downpour from the monsoon thunderstorms spurs plant growth. Desert plants absorb moisture to sustain themselves after the wet season ends.
The monsoon rains are always welcome, but also dangerous. Flooding and wind damage is common. All over Arizona, you will see dry riverbeds called washes. During monsoon season, these washes can fill with water very suddenly.
Every season, flash flooding happens and cars, people and even cattle become stranded or washed away.
Sadly, monsoon season also can make a tender box fire season even worse, due to the increased amount of lightning, up to tens of thousands of strikes per night in some areas.
Yes, life in the desert can be harsh. The unique weather patterns and monster storms remind me of the volatility of this rock we’re living on. The vivid bursts of plants, cacti and wildlife show how life can survive, and flourish, in the harshest environment. And the brief monsoon proves with stark reality how precious our water supply is to our survival.
Good lessons, all, don't you think?