ALBUQUERQUE – This year, new Mexican officials have a message to farmers who depend on irrigation water from the Rio Grande and other rivers: If you don’t absolutely have to plant this year, don’t.
Years of warming temperatures, a failed rainy season last summer, and low snowpack this winter have helped reduce the state’s rivers to a relative trickle. The authority that controls the irrigation flows on the Rio Grande has forced the problem. To save water, it opened its doors a month later than usual.
Severe drought – mostly related to climate change – devastated not only New Mexico, but the entire western half of the United States, from the Pacific coast to the Great Basin and the southwestern desert to the Rocky Mountains and the Northern Plains.
In California, wells are drying up, forcing some homeowners to drill new ones that are deeper and more expensive. Lake Mead, on the Arizona-Nevada border, has been so severely cleared of water from the Colorado River that the two states may face a potential cut in their supplies. And 1,200 miles away in North Dakota, ranchers pull water for cattle and give them extra fodder as the heat and drought slow down spring growth on the rangelands.
The most significant, and possibly deadliest, effect of a drought as severe and widespread as it is in the west is the forest fires, which rage in hot and dry conditions. And that’s long before the full heat of summer hits.
California, Arizona, and New Mexico each had two large flames, which were unusual earlier in the year. None have been completely contained, including the Palisades Fire, which burned 1,200 acres on the outskirts of Los Angeles.
Officials predict when the fire season ends – if it ever does, as warming conditions in some areas have made fires possible year-round – the total for last year could exceed 10.3 million acres.
“The signals and signs suggest that we are approaching another very dangerous year of fire,” said Agriculture Secretary Tom Vilsack, whose department the Forest Service belongs to, last week after receiving briefings from National Interagency Fire experts on him and Home Secretary Deb Haaland Center. “We see a higher risk and an earlier risk than in the past.”
Many factors contribute to the frequency, intensity and duration of forest fires, including forest management practices and development. Water scarcity is affected by population and economic growth, as well as the pumping of groundwater for agriculture and other activities.
Legal restrictions also play a role. Part of the pressure on farmers in New Mexico this year is that the state of Texas owes Rio Grande water under a 1938 agreement.
However, the root of the drought is warmer temperatures and changing rainfall patterns associated with the emission of carbon dioxide and other greenhouse gases into the atmosphere, where they trap the heat of the sun. The result was extremely arid conditions that have existed for years in much of the Southwest and California and spread throughout the west.
According to the United States Drought Monitor, 84 percent of the west is currently in drought, 47 percent are classified as “severe” or “extreme”.
The situation in some states is particularly dire. In Utah, 90 percent of the state is in the two most severe categories; in Arizona, 87 percent; North Dakota, 85 percent; New Mexico, 80 percent; and California 73 percent.
Experts don’t see much chance of improvement as another hot and dry summer is forecast. Rather, they expect conditions to deteriorate.
“We are entering the climatically dry time of the year,” said Adam T. Hartman, a meteorologist with the Climate Prediction Center, part of the National Oceanic and Atmospheric Administration. “That is one of the reasons the drought conditions are gradually worsening.”
The southwest had its chances of improving starting last summer, a time of year when atmospheric circulation patterns typically bring tropical moisture to Arizona, New Mexico, and parts of the nearby states. But these so-called monsoons never happened, and no one knows exactly why. “It’s a bit of a puzzle,” said Mr. Hartman.
That winter’s snowfall, or the relative lack of it, didn’t help either. The total amount of snowpack in the west was well below normal. In California, national snowpack was only 59 percent of the historical average on April 1, the date when snow is typically deepest.
Much of the west is usually relatively dry compared to the often humid conditions in the east. But with warming, precipitation has become less reliable, said Keith Musselman, a snow hydrologist at the University of Colorado. “These are regions that regularly pass weeks of no rainfall,” he said. “And now we’re talking for months in some cases.”
Especially in the southwest, the drought has lasted so long – since 2000, with only a few humid years – that climatologists are now speaking of an emerging megadrought that can rival those that have occurred at regular intervals over the past thousand years . Those megadroughts in the southwest, discovered by analyzing old tree rings, lasted for decades – in one case 80 years.
California and other western states rely on snow melting for much of their water. The snowpack is essentially a frozen reservoir that is released over time in spring and summer. But that too will change when the West warms up.
“There are two things,” said Dr. Musselman. “First, there is less rainfall. But on top of that there is this background of warming. That changes the delivery of this water. “
In the past, more meltwater flows off the mountains, which leads to chaos and offers the possibility of storing adequate amounts in reservoirs for the dry summer. Too much drainage too early ultimately also leads to a rapid drop in electricity flows.
Low current flows can lead to a number of other problems as the shallower water heats up faster. In California, for example, some salmon hatcheries are shipping young fish straight to the ocean this spring because they fear they won’t survive swimming in the warmer waters of drought-hit rivers.
Heat and drought have a particularly strong impact on conditions that lead to forest fires, reducing moisture in the soil, and drying vegetation so that it ignites more easily and burns hotter. This makes it easier for fires to spread.
Severe drought can also kill trees and provide enormous amounts of fuel for potential fires. The Forest Service reported one such dieback in April in Arizona, where up to 30 percent of juniper trees in approximately 100,000 acres had died from the drought.
Arid conditions can also make warming worse, said Amir AghaKouchak, who studies climate-related and other water resource issues at the University of California at Irvine. As a result of warming, the soil loses moisture through evaporation, which has a cooling effect on the surface of the soil, just as a person cools down through the evaporation of sweat from the skin. But at some point so much soil moisture is lost that the process stops.
“During periods of drought, the moisture content becomes very low so evaporation does not occur,” said Dr. AghaKouchak. “The skin of the earth heats up and that heats the atmosphere.”