The western US may be experiencing the worst drought in modern history

Extreme drought in the western US has become as reliable as a summer afternoon thunderstorm in Florida. And drought news headlines in the West may look a bit like a broken record, with some scientists saying the region is on the precipice of permanent drought.

That’s because in 2000 the western US was entering the beginnings of what scientists call a megadrought – the second worst in 1,200 years – caused by a combination of a natural dry cycle and man-made climate change

In the last 20 years, the two worst droughts came in 2003 and 2013 – but what is happening now seems to be the early stages of something even more serious. And as we enter the dry summer season, the stage is set for an escalation of extremely dry conditions, with widespread water restrictions expected and another dangerous fire season ahead.

The above image is a time series of droughts in the western states from 2000 to 2021. This last peak from 2020-2021 (on the right) is just as impressive as the others, but with one notable difference – this time the area is ” exceptional drought “is much greater than any other peak, with an air coverage of more than 20%. As we enter the dry season, there is little chance that conditions will get better – in fact, it will only get drier.

With this in mind, there is no doubt that the drought in the West, especially in the Southwest, will be the most intense in recent memory this summer and fall. The only real question: will it last as long as the last protracted drought from 2012 to 2017? Time will tell.

Currently, the US Drought Monitor places 60% of Western states under severe, extreme, or exceptional drought. The reason for the extensive drought is twofold; long-term drying fueled by man-made climate change and, in the short term, an event in La Niña where cool waters of the Equatorial Pacific did not provide enough moisture.

As a result, last winter’s wet season was not very wet at all. In fact, it was only getting worse, with only 25 to 50 percent of the normal rainfall in much of the Southwest and California. This followed one of the driest and hottest summers in modern times, with two historic heat waves, a summer monsoon cycle that just didn’t even show up, and the worst fire season in modern times.

The image below shows what is called the precipitation percentile from October through March, comparing the last six months with the same six-month period in each of the past 50 years.

The light brown shading shows areas in which the most recent six-monthly trajectory was in the driest 10% of the last 50 years. The dark brown hue indicates the areas with the lowest rainfall ever recorded during this last six-month period. Almost all areas fall under one of those two shades.

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

However, the Pacific Northwest is doing very differently this season. The northern half of the West experienced normal to even above normal snowfall this winter, similar to what is expected during a typical La Niña event with a further northern jetstream storm track. That luck didn’t extend further south, however, with most areas now at only 50 to 75% of the normal snowpack.

Since the West relies on melting snow cover to fill lakes, reservoirs and rivers like the Colorado, water availability will be limited this summer. The Colorado River and its tributaries provide water to approximately 40 million people and 5 million acres of farmland. The amount of water flowing into Lake Powell, on the state border between Arizona and Utah, in the coming months is expected to be only about 45% of the normal amount. Lake Meade, on the state border between Arizona and Nevada, has only a 40% capacity.

But this lack of snowpack is not a one-time problem; it is a trend. Over the past 40 years, snowpack in the western states has decreased by about 25%. Meanwhile, the population continues to increase. So lately the demand for water has exceeded what Mother Nature can provide.

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 man-made climate change, leading to less reliable rain and warmer temperatures – both consistent with what has been projected by climate computer models. The image below shows a clear trend towards worsening drought since 1900.

New research from the United States Department of Agriculture shows that rainfall has become more erratic in recent decades and the dry spells between rains have increased. Even if rain or snow is heavier, that’s less important than consistency. Soil moisture and vegetation thrive on precipitation that is more evenly distributed over time, rather than severe events that tend to drain, resulting in wasted moisture.

At the same time, temperatures in the western US have risen 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 soil continues to dry out, yielding combustible fuel escalating fireseason

In fact, 2020 was the worst fire season in the West’s modern history, with California and Colorado having their biggest fires ever. As can be seen in the picture below, the intensity of fires and acres of burnt spores is with rising temperatures. Simply put, the warmer and drier it gets, the bigger the fire gets.

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. That means, with the dry season already underway in the West, the time to prepare for wildfires is fast approaching.