The deserts of the American Southwest and northern Mexico are, like most deserts, caused by a rain shadow - in this case produced by the coastal mountains of California and West Mexico. The deserts or semideserts extend as far north as southern British Columbia, but my experience is mostly with the more southern Chihuahuan and Sonoran Deserts in New Mexico, Texas, Arizona and California in the United States and in northern Mexico, including much of Baja California, Sonora and Chihuahua, and to a lesser extent, with the Mojave Desert in California and northwestern Arizona. These generally receive 10 inches (250 mm) or less of rain a year, with Yuma at less than three inches (75 mm) and Tucson around 12 inches (300 mm), although the surrounding land is certainly desert. In the Mesilla Valley of New Mexico, where I currently live, the rainfall is on average about 8 inches (200 mm), but so far this year my backyard rain gage has registered only 21 mm, or about a tenth of our normal yearly rainfall.
In the Southwestern deserts we think a lot about water. Most agriculture is a result of either irrigation from rivers (the Colorado and Rio Grande especially) or from wells. The recent drought in the Southwest is already the worst since records have been kept and it shows no sign of letting up. Indeed, water is the main limiting factor for just about any activity in the desert Southwest. I always remembered to carry the precious liquid with me when I hiked into the desert when I was growing up near and in Yuma because I well knew that the drylands are unforgiving of fools.
A Great Blue Heron in a threatened habitat - marshes along the Rio Grande in New Mexico.
The rivers in the area - the Colorado and its associated Gila, Salt and Little Colorado Rivers, the Rio Grande with its associated Pecos and Rio Conchos - are such complex subjects that whole books have been written about many of them. Because of this I will concentrate in this diary only on the springs, tanks (tinajas) and playa lakes. Even so I can only barely touch on the subject!
Water holes in the desert are usually rain catchments or, if you are lucky, they may be spring fed. Even so, in droughts I have seen desert springs completely dry up. In some areas the water from springs was pure enough to drink - I well remember the cold pure water from Italian Springs in the Rincon Mountains above Tucson. However most water you might run across in the desert should probably be boiled or filtered. Two hikers in the Rincons found this out while I lived in Tucson when, in drinking water from a temporary stream in the mountains, they developed nice cases of dysentery. Giardiasis is also a real danger. Still water is always a welcome surprise in the desert and one that usually provides interesting observations of the desert's surprisingly varied biota.
Possibly the most famous of all the water tanks (tinajas) in southern Arizona are those of Tinajas Altas along the Camino del Diablo of Yuma County near the Mexican border. The lower tanks are easy to reach (or so I have read - I never reached them myself, but have seen the Tinajas Altas Mountains from both sides), but the upper tanks are difficult to reach, involving some rock climbing. When the lower tanks, which are shallower, dried up, weakened travelers often died of thirst before they could reach the more permanent ones. Thus there were many graves just below the lower tanks, dug by those who succeeded in reaching the water holes and were strong enough to bury the bodies.
Horse Tanks in the Castle Dome Mountains of Yuma County, are more accessible, but some of the tanks are very deep and treacherous. I remember a deer carcass being in one of the deep tanks, the animal having apparently fallen in and found itself unable to climb the steep rock walls. Baker Tanks, south of Interstate 8 (then U.S. 80) near Welton, also in Yuma County, were even more available, and do not have that many deep tanks.
In Big Bend Ranch State Park in Texas I visited Cinco Tinajas, which were easy to reach, but like Horse Tanks have some water holes that are very difficult to reach or leave once they are reached! Some shallow water holes there contained numerous dragonfly and damselfly nymphs when I was there.
The tanks I saw were in areas that had been sculpted by water. There had been serious floods in these areas over the millennia, some of which scoured the bed rock to the point of smoothness. The two most common causes of death in the desert are thirst and drowning! Given the right circumstances it is very easy to have either happen to a traveler, which is a good reason one should never enter a desert without a bit of knowledge and a full canteen!
Springs, such as Aguirre and Dripping Springs in the Organ Mountains of New Mexico, Italian Springs in the Rincon Mountains of Arizona, and Ojito Adentro in the Big Bend of Texas, are very important to the local wildlife. Ojito Adentro is a case in point. When I visited there a few years ago the spring was running and maidenhair ferns grew on the bank where water cascaded down from the spring. The riffles below the falls contained dryopid beetles, probably an extremely localized population. Poison oak and grapevines covered the surrounding area under the willows and cottonwoods and buttonbush was in full bloom, drawing butterflies for miles.
A Texas Longhorn with the desert spring oasis Ojito Adentro in the background. Big Bend Ranch State Park, Texas.
Even playa lakes, which are often dry expanses of alkali flats during most of the year, can become animated when filled with water. Isaac's Lake in New Mexico has periodically filled, to become full of tadpole shrimp (Triops sp.), Triassic relics whose eggs can survive in the lake bed for years. In between fillings by rain water there seemed to be a yearly change in the dominate plants covering the lakebed - sometimes blueweed, sometimes buffalo burr, sometimes grasses.
Bitter Lake, near Roswell, is highly alkaline and, as the water receded during drought, would become ringed with pinkish colonies of halophilic (salt loving) archaebacteria. Both Bitter Lake and Willcox Playa in Arizona have their associated populations of tiger beetles, although the Arizona playa seems to have the highest biodiversity of these fast moving predators. Bitter Lake National Wildlife Refuge has one of the highest, if not the highest, number of associated dragonflies and damselflies in the United States, with somewhere around 100 species. Bitter Lake NWR also has several endangered species associated with its numerous sinkholes and the man-made ponds along the nearby Pecos River are host to large numbers of ducks during migration. To the south of Bitter Lake lies Bottomless Lakes State Park, which also teams with life.
Water has always been a precious resource in the Southwest and irrigation canals were and are important to communities. Even today their are irrigation associations that have been in existence for as long as 400 years in New Mexico and southern Colorado. Such acequia associations are common in New Mexico and the cooperative nature of association laws makes these very important, not just to water conservation, but as a refuge for wildlife and rare plants.
The current drought is, of course, wreaking havoc on the biota. When springs that have usually been there even in very dry periods, vanish, the local animals have difficulty finding needed moisture. Often homes and urban areas may be invaded by larger animals seeking both water and food. Bobcats, pumas and bears become unwelcome guests, but one can hardly blame them. A few mammals, like kangaroo rats, can make their own water from seeds, but most need at least occasionally to drink.
The drought is also causing other problems - more frequent and more severe brush and forest fires, higher dependence on vanishing underground aquifers, and the associated legal problems involved in often convoluted water rights laws. Water can literally cause legal and sometimes violent confrontations. As global warming ramps up this will almost certainly get worse, but it would have perhaps anyway, as population and industry put more pressure on our limited supply of fresh water. Only 2.5% of the earth's water supply is fresh and desalination is expensive. In truth drinkable and irrigable water is more precious than oil, natural gas, Uranium, coal, or any other material extracted from the earth. We simply cannot live without it!
I have only touched on the complexity of water issues in the arid Southwest. And certainly water remains the major limiting factor throughout the planet, not just in historically dry areas. In some areas both pollution and demand are causing usable drinking and irrigation water to become increasingly scarce. It is an inconvenient truism that one person can in short order poison a well or mess up a creek. Yet, we have millions of polluters and their associated industries doing the same. In the end one cannot eat gold (as was said by a Native American many years ago) and one can certainly not drink it! Fracking and such projects as the Keystone XL pipeline and the proposed Pebble Mine in Alaska can well ruin us. When the water runs out we are finished!
References: I could not begin to list all the possible references on this subject, but a few of my favorites will have to suffice.
Childs, Craig. 2000. The Secret Knowledge of Water. Little, Brown and Co. Boston.
Hartman, William K. 1989. Desert Heart. Fisher Books, Tucson.
Where is Earth's Water? http://ga.water.usgs.gov/...
As usual the photos are by me!