The western United States may be entering the most severe drought in modern history

Extreme drought in the western United States has become as unreliable as a summer thunderstorm in Florida. And headlines about drought in the West may seem a bit of a record, with some scientists saying the region is on the brink of permanent drought.

This is because in 2000 the western US entered the beginning of what scientists call a megadrought – The second worst in 1,200 years: triggered by a combination of a natural, human-caused dry cycle climate change.

In the last twenty years, the two worst stretches of drought occurred in 2003 and 2013, but what is happening now seems to be the initial stages of something even more serious. And as we enter the dry summer season, the stage is set for an escalation of extreme dry conditions, with widespread water restrictions in place and another dangerous fire season ahead.

The image above is a time series of droughts in the western states from 2000 to 2021. This last 2020-2021 rise (right) is as impressive as the others, but with one notable difference: this time, the area of ​​“exceptional drought “is much larger than any other tip, with over 20% air coverage. When we enter the dry season, conditions are very unlikely to improve; in fact, they will probably just dry out.

Given this, there is little doubt that the drought in the West, especially in the Southwest, this summer and fall will be the most intense in recent memory. The only real question: will it last as long as the last prolonged drought period from 2012 to 2017? Only time will tell.

Right now, the U.S. Drought Monitor places 60% of Western states in severe, extreme, or exceptional drought. The reason for the extensive drought is twofold; a long-term drying fueled by human-caused climate change and, in the short term, an event in La Niña in which the cold waters of the equatorial Pacific failed to feed a large amount of moisture.

Consequently, this past winter’s rainy season was not at all wet. In fact, it only added insult to injury, with only 25 to 50 percent of normal rainfall falling in much of southwestern and California. This followed one of the driest and hottest summers of modern times, with two historic heat waves, a cycle of summer monsoons that simply didn’t show up, and the worst fire season of modern times.

The following image shows the so-called precipitation percentile from October to March, comparing the last six months with the same six-month stretch of each of the last 50 years.

The light brown shade shows areas where the most recent six-month stretch has been 10% drier over the past 50 years. The shade of dark brown indicates the areas that recorded the lowest rainfall recorded during the last six months. Almost all areas are covered by one of these two shades.

Kelsey Satalino, digital communications coordinator for NOAA’s National Integrated Drought Information System, says that in recent months, several states, including Nevada, Arizona, New Mexico and Utah, have experienced their most severe drought. since the Drought Monitor began in 2000. As a result, soil moisture content is at its lowest levels in at least 120 years.

The Pacific Northwest, however, is going very differently this season. The northern half of the west normally experienced even above normal snowfall this winter, as expected during a typical La Niña event with another storm runway from the jet stream. However, this good fortune did not spread south, as most areas only have between 50 and 75% of the normal snow mass.

Since the West depends on melting snow to fill lakes, reservoirs and rivers, such as Colorado, water availability will be limited this summer. The Colorado River and its tributaries provide water to about 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, has only 40% capacity.

But this lack of a snowpack is not a single issue; it is a trend. In the last 40 years, the snow package has decreased by about 25% compared to western states. Meanwhile, the population continues to grow. Thus, recently, the demand for water has exceeded what Mother Nature can offer.

In general, these water problems are not expected to improve. Although there will be wet years, the general trend is towards drying. Scientists say this is the result of human-caused climate change, leading to less reliable rainfall and warmer temperatures, both consistent with what climate computer models have projected. The following image shows a clear trend towards a worsening drought since 1900.

New research from the U.S. Department of Agriculture shows that rainfall has become more erratic in recent decades and that dry periods between rainstorms have widened. Even if rain or snow falls more intensely, it is less important than consistency. Soil moisture and vegetation thrive with rainfall that spreads more evenly over time, rather than strong events that tend to run off, causing a loss of moisture.

At the same time, temperatures in the western United States have risen a few degrees in the last 50 years. Warmer air provides more heat energy to evaporate moisture from vegetation and soil. As a result, the soil continues to dry out and provides flammable fuel fire season climbs.

In fact, 2020 was the worst fire season in modern Western history, with California and Colorado experiencing their largest fires on record. As you can see in the image below, the intensity of the fires and acres burned tracks with rising temperatures. Simply put, the hotter and drier it becomes, the bigger they become fires.

Due to a warming climate, the fire season in the West is now two to three months longer than it was a few decades ago. This means that as the dry season begins in the West, the time to prepare for forest fires is fast approaching.