Worst drought in modern history may hit Western U.S.

Extreme drought may be going to hit across the Western U.S. Some scientists saying the region is on the precipice of permanent drought.

In 2000, the Western U.S. entered the beginning of what scientists call a megadrought — the second worst in 1,200 years — triggered by a combination of a natural dry cycle and human-caused climate change.

The U.S. Drought Monitor places 60% of the Western states under severe, extreme or exceptional drought. The reason for the extensive drought is two-fold; long term drying fueled by human-caused climate change and, in the short term, a La Niña event in which cool Equatorial Pacific waters failed to fuel an ample fetch of moisture.

United States Drought Monitor said:

As the wet season begins to wind down in the West, widespread extreme (D3) to exceptional (D4) drought continues across much of the Southwest. Another week of warm, dry weather did not help. High temperatures ranged from 4 degrees above normal in the Northwest to 15 degrees above normal in the Southwest while little to no precipitation fell across much of the region. Where exceptions occurred, in the Pacific Northwest and the Northern Rockies, totals generally were not enough to overcome shortages. In eastern Washington, abnormal dryness (D0) and moderate drought (D1) expanded as precipitation deficits continued to increase, drying out soils. Conditions also deteriorated in Oregon. Most notably, D3 expanded and D4 was introduced in south central Oregon in response to record low water-year-to-date total precipitation, streamflow and soil moisture. It’s worth noting that since the U.S. Drought Monitor began in 2000, this is only the third time that D4 has occurred in the state, and only the second time that more than one percentage point of D4 has occurred. (In 2015, 0.1% of the state experienced D4 for two weeks in April. In 2003, there were 25 weeks of drought that included D4.) In California, the April 1 snow survey showed that snow water content in the Sierra Nevada Mountains was at 59% of average and the state, as a whole, received about 50% of its average precipitation for the water year. Two consecutive dry years have left reservoirs about half full. These precipitation deficits, combined with high temperatures, have reduced streamflow, dried out soils, and stressed vegetation. Changes to this week’s map include an expansion of D3 in northern California and western Nevada and an expansion of D2 (severe drought) and D3 in southern California. D1 expanded in northwest Wyoming and southeast Montana to reflect below normal precipitation over the water year and its effect on soil moisture and streamflow. Eastern Montana also saw deteriorating conditions with an expansion of D2 and D3. Here, the lack of precipitation over the last 2 to 3 months has dried out soils and stressed vegetation. USDA reports that, as of April 4, 76% of the state’s topsoil was rated short to very short indicating that soil moisture supplies are significantly less than what is required for normal crop growth development.

Media reports from the U.S., including reports by The Washington Post and CBS said:

The Western US is in the midst of yet another dangerous dry spell. The drought has been building over the past year, and since November, a greater stretch of the West has been in the most severe category of drought than at any time in the 20 years that the National Drought Mitigation Center has been keeping records.

Western states are already facing water shortages, and with the National Weather Service projecting that the dry stretch will continue, the problems that accompany droughts are likely to pile up heading into this summer.

During California’s last major drought, residential wells ran dry, students had to shower in their school locker rooms. To keep toilets running, some rural households relied on hoses slung over fences from their neighbors.

With groundwater depleted by that drought, which only ended in 2017, and ongoing overuse of water on farms, families have had to dig deeper wells, which can be prohibitively expensive.

That last drought also led to other fallouts: billions of dollars in economic losses as farmers were forced to let fields lie fallow and a 50 percent drop in electricity production from dams. It also contributed to the death of over 100 million trees, which fuels bigger wildfires, like the ones that ripped through the West last summer. If the current drought continues, similarly stark consequences lie ahead.

Climate change is driving more severe droughts and spurring longer, more troubling “megadroughts” across the Western states.

The West was relatively drought-free after a wet winter in 2019. But by now, the region has swung from 27 percent in drought to 77 percent, according to the latest data from the US Drought Monitor released March 11.

Over the past year, the drought has been building due to a lack of rain, a weak summer monsoon in the Southwest, and intense summer heat waves. “If I had to pinpoint one thing that really drove the drought to where we are right now, it was the heat of last summer,” said Brian Fuchs, a climatologist at the University of Nebraska’s National Drought Mitigation Center.

High summer temperatures sucked the moisture out of the soil and evaporated water resources.

The Four Corners, where Utah, Arizona, New Mexico, and Colorado meet, has been the epicenter of this drought, Fuchs said. The dark splotch on the map below shows that those states as well as Nevada have been experiencing the most intense drought.

US Drought Monitor

US Drought Monitor

Now the West is in the winter wet season, but due, in part, to the La Niña weather pattern, too little rain and snow is falling to make up for the preceding dry months.

Some rain and snow may still fall, but the National Weather Service’s seasonal forecast projects that drought conditions will persist across the Western U.S. through May, the end of the current forecast period. “We do have some time to maybe put a dent in some of these deficits that we’ve seen through the winter,” said Fuchs. “Now the idea that we are going to catch up completely — that’s going to be tough.”

The trajectory of this drought episode remains unclear, but scientists say that it is actually part of a bigger megadrought — a decades-long dry spell, punctuated by severe droughts. This megadrought began around 2000, and as the chart below shows, the majority of land in the West has been in some level of drought ever since.


Over the past 20 years, the Western US has experienced frequent severe droughts, which together form a megadrought. (The Y-axis shows the percent of Western land that is in some kind of drought. The darker colors represent more severe categories of drought.) US Drought Monitor

Based on data from tree rings and other ecological records of weather and climate patterns of the last few thousand years, we know that the West is no stranger to drought. In an April 2020 tree ring study published in Science, researchers found that several megadroughts occurred between 850 and 1600 — before humans started pumping massive amounts of greenhouse gases into the atmosphere. These droughts were likely caused by cool temperatures in the Pacific Ocean that prevented rainfall from reaching the Southwest.

While natural variability has been a factor in recent droughts, the current megadrought is also being driven by climate change, according to the study. Higher temperatures, caused by greenhouse gases, have increased evaporation and decreased precipitation in the spring across the region. The researchers were able to identify that climate change accounted for 46 percent of the drought’s severity.

Without climate change, there still would have been a drought, but “anthropogenic warming was critical for placing 2000–2018 on a trajectory consistent with the most severe past megadroughts,” they wrote. The current megadrought, which they traced from 2000 through 2018, was the second driest 19-year episode in the 1,200-year record.

This finding is not just important for how we understand the current crisis, but also for the coming decades in the Western US as temperatures continue to climb.

The latest National Climate Assessment, authored by 13 U.S. federal agencies in 2018, laid out a grim future for the Southwestern states: Rising temperatures will increase the likelihood of megadroughts in the region and make droughts more frequent and severe, according to the scientific literature cited.

While annual precipitation in the Southwest may not necessarily decrease, the hotter annual temperatures will burn off more moisture, contributing to droughts, the researchers explained in the Science tree ring study.

Communities across the West have already felt the impacts of the latest drought, starting with last year’s devastating wildfires. The growing drought over the summer dried out vegetation, priming the landscape to burn.

Now, as water reserves plummet, New Mexico state officials are encouraging farmers to not plant crops, the Wall Street Journal reported. Reservoirs are also troublingly low in California, and snowpack — which serves as a critical water bank for the state — is at 61 percent of the average for early March.

Due to the role of climate change, preventing the worst outcomes from drought going forward starts with reducing greenhouse gas emissions as fast as possible.

After the last drought, California put in place its first groundwater management law as well as conservation directives that decreased water use by 25 percent between 2014 and 2017. But for the 2 million Californians who rely on wells, many of whom live in marginalized communities in rural areas, the situation is still precarious. During the last drought, farmers increasingly turned to pumping groundwater, which caused thousands of neighboring drinking water wells to fail by the end of the drought.

According to Erick Orellana, a policy advocate at the Community Water Center, this could happen again because the existing groundwater laws do not prioritize these communities. “The fact is that, currently, California does not have preparedness plans in place for the most vulnerable communities,” he said. Current regional plans under the state’s groundwater management law would allow thousands of wells to go dry, the Guardian reported.

Last month, California Senate Majority Leader Bob Hertzberg introduced Senate Bill 552, which would require smaller water systems in California to create drought preparedness plans.

Three-quarters of annual water consumption in the Southwest goes to irrigating crops, and populations are growing in cities that are naturally dry. In St. George, a city in southern Utah’s Washington County, a construction boom is straining water demand amid the drought.

In the San Joaquin Valley, as aquifers drop, researchers say current levels of agricultural water use are untenable. A few months ago, the Community Water Center in San Joaquin started fielding calls for help from people losing water access once again. “The calls we were getting last summer really just gave me a major sense of deja vu to 2014,” Jensen said.

In several states including Nevada, Arizona, New Mexico and Utah, soil moisture content is at its lowest levels in at least 120 years.

Since the West relies on melting snowpack to fill lakes, reservoirs and rivers, like the Colorado, water availability will be limited this summer. The Colorado River and its tributaries provide water for around 40 million people and 5 million acres of farmland. The amount of water flowing into Lake Powell, on the Arizona-Utah state line, in the coming months is only expected to be around 45% of the typical amount. Lake Meade, on the Arizona-Nevada state line, is only at 40% capacity.

But this lack of snowpack is not a one-time issue; it is a trend. Over the past 40 years, snowpack has declined by about 25% over the Western states. Meanwhile, the population continues to increase. Thus, as of late, water demand has been outstripping what mother nature can deliver.

While there will be wet years, the overall trend is towards drying. Scientists say this is a result of human-caused climate change, which is leading to less reliable rain and warmer temperatures — both consistent with what has been projected by climate computer models.

New research from the U.S. Department of Agriculture shows that over the past several decades, precipitation has become more erratic and dry periods between rain storms have expanded. Even if rain or snow falls heavier, that is less important than consistency. Soil moisture and vegetation thrive on precipitation that is spread out more evenly over time, rather than heavy events, which tend to run-off, resulting in wasted moisture.

At the same time, temperatures across the Western U.S. have increased by a few degrees over the past 50 years. The warmer air provides more heat energy to evaporate moisture from vegetation and soil. As a result, the ground continues to dry out, providing flammable fuel for escalating fire seasons.

In fact, 2020 was the worst fire season in the modern history of the West, with California and Colorado experiencing their largest fires on record.

Because of a warming climate, fire season in the West is now two to three months longer than it was just a few decades ago. That means, with the dry season already getting underway in the West, the time to prepare for wildfires is fast approaching.

In California, last year’s more moderate rainfall deficits, combined with extreme heat waves, ushered in a record-setting fire year. It brought 5 of the 6 largest fires in modern state history, 10,488 destroyed structures and 33 fatalities. Some 4.2 million acres were torched.

For the last two wet seasons, a persistent ridge of high pressure in the central and eastern Pacific has diverted most storms out of California. In Northern California, many of the wettest, forested regions have missed over 20 inches of precipitation in that time.

Last week in the Santa Cruz mountains, Craig Clements, a professor and director of the Wildfire Interdisciplinary Research Center at San Jose State University, sampled plants in a field of chaparral — flammable shrubs found throughout the state. They showed record low moisture values for April and no new growth where they should be blooming and thriving.

September’s Creek Fire in the southern Sierra burned through a massive accumulation of woody debris from the previous drought and was turbocharged by a record-setting Labor Day weekend heat wave.

Even with the very dry spring so far, grasses are still green in many areas, preventing fires from spreading quickly. But once those dry out, or “cure,” the state could be in a full-blown fire season.

In Southern California, grasses could carry fire by late April, about on schedule, according to Matt Shameson, a fire meteorologist with the U.S. Forest Service in Riverside, Calif.

While wind events are not common in late spring, some are possible in May, including warm “Sundowner” land-to-sea winds that can affect coastal Santa Barbara County this time of year and have driven dangerous fires near urbanized areas.

The West’s descent into the current severe and widespread drought began in the fall of 2019, when a dry pattern emerged over Oregon, northern California, central Nevada and into parts of Idaho, Utah and Colorado.

Extremely warm and dry conditions from October to March extended across California and Oregon, and eastward across Idaho, Nevada, Utah, Arizona, and entering Wyoming, Colorado, and New Mexico.



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