Adiabatic—a what?

If you listen to the explanations given by weather forecasters, you may have heard the word adiabatic.

No, it’s not a disease related to blood sugat—that has a BET in the middle, not a BAT.

Instead, it is one very cool reason that storms suddenly pop up out of a clear sky in the desert.

Adiabatic cooling or warming happens when the pressure on a blob of air increases or decreases. When desert air hits a mountainside and rushes up the mountain, the air expands, gets “thinner” and cools as it rises to a higher elevation.

This means that if there is any moisture in the air, there is less energy to keep it suspended, so the moisture is more likely to condense, and form rain.

The opposite happens when air flows downslope—it warms as the pressure increases because the molecules are closer together and bump into each other more.

Maybe that is one reason that places east of mountains in North America are often more warm and dry than places to the west of mountains. Not only does the moisture get wrung out of the air on the western upslope, even very wet air from the ocean, but following that, some of the moisture on the downslope gets absorbed back into the falling, compressing, warming air.

Cool!

Or rather, cool, then warmer and drier!

 

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Limiting Factors—Cold!

If you were in the Sonoran desert in January 2013, you may well have experienced a limiting factor that many people would not expect in a desert: freezing damaging cold.

In many places it dropped into the 20’s or lower at night, for several nights, enough to nip many buds in the bud.

Native plants, which have been through this before, generally survived quite well, but imports, or annual vegetables, either got crisped or completely melted down.

This suggests that planting native species has even more benefits than we usually consider.

Spring Planting

A Dry Heat

The joke is, in the Sonoran desert, even though it’s 114, it’s a dry heat.

The idea being that with very low humidity, amazingly, under 5 percent at times, the heat is easier to bear.

114, an average high for a few days each summer, is still bad enough, but given how few trees and other shelter there is in the desert, it’s almost always a sunny heat during the daytime, which adds another 7 to 10 degrees.

All plants and animals and people that live in the desert need to be built or adapt in some way to survive these extreme temperatures.

The hottest time of year is a few days before the summer Solstice on June 21, and a few weeks after that. Then the average daily temperature starts going down again, very very gradually.

A few weeks after the solstice is also the time when the summer monsoons really get going. The standard definition of monsoon season is the change in the wind, but in the desert, the important thing is that the monsoon usually brings moisture and finally rain from the Gulf of California and the Gulf of Mexico.

And of course, when the humidity goes up and the rains start, it’s still over 100 degrees in the desert. And it’s no longer a dry heat.

What are Desert Wetlands?

The definition of desert is a dry place. So what do you mean, desert wetlands? Like most things in nature, deserts are more complicated, and interesting, that you’d think at first.

For example, there are many kinds of wetlands found in or near deserts:
Ponds
Freshwater and Salt or Alkaline lakes, like the Great Salt Lake
Springs and Seeps
Creeks, Streams and Rivers
Intermittent Streams, like the Hassayampa River
Disappearing Streams, like the Hassayampa River
Canals, Impoundments and other built wetlands
Oceans

Because they are such a distinct change or edge, they often host a surprising variety to wildlife, including disjunct species, that is, organisms typically found in distant areas.

This also means that they are often good places to view wildlife.