Hot, dry conditions are exacerbating the drought in California | MCUTimes

Hot, dry conditions are exacerbating the drought in California

Rising evaporation demand is escalating the severity of summer droughts in California and the West, according to climate scientists.

Evaporation needs are essentially the “thirst” of the atmosphere. It is calculated based on temperature, humidity, wind speed and solar radiation. It is the sum of evaporation and transpiration from plants, and it is driven by warmer global temperatures, which can be attributed to climate change.

The meteorological summer of 2021 in the contiguous United States, which runs from June to August, tied the extreme heat of the Dust Bowl summer of 1936.

Evaporation demand has driven nearly half of California into what the U.S. drought monitor calls “extraordinary drought.” It causes faster drying of soil and vegetation, making fuels more dangerously combustible during the summer and fall, the peak of California’s fire season. As a result, fuels burn faster and hotter.

California and the West have seen a significant increase in evaporation demand over the past half century, exacerbating the severity of summer droughts, says John Abatzoglou, associate professor and climate scientist at UC Merced.

The drought in California is not just a result of a lack of rainfall. It is a combination of two things: lack of rain and the thirsty atmospheric conditions that are drying up the landscape. For large parts of California, the summer and water years of 2021 have had the highest evaporation needs in the last 40 years, according to the National Integrated Drought Information System.

As Abatzoglou points out, Northern California has endured the third driest water year on record along with the highest evaporated demand factors that “place this year in a class of its own.” These things are remarkable, he adds, “since the infamous drought hall in California is infamous.”

Abatzoglou refers to the Palmer Drought Severity Index, which he describes as a general drought index that is widespread in the United States and part of it that informs U.S. drought surveillance. By that standard, Northern California has its worst year on the instrumental record. PDSI is a soil moisture index that accounts for both precipitation and evaporation needs.

Abatzoglou sees the “demand” side of the drought as something we are beginning to appreciate. He says there has been drought and then there has been heat and dry drought. The latter has promoted increased summer irrigation requirements from agriculture in the Central Valley, energy balances due to greater demand caused by heat and reduced energy supply due to the reduction in hydropower production.

A chart shows the Palmer Drought Severity Index in Northern California since 1900, with 2021 being the worst

In some droughts, Northern California has had its worst year on record.

(Paul Duginski / Los Angeles Times)

The latest U.S. drought monitoring report, released Thursday, paints a grim picture of the situation in California and large parts of the West – as it has done for several months. In the current data, about 46% of the state is categorized as being in extraordinary drought, while just over 42% are in extreme drought. The remaining approximately 12% of the state is approximately evenly distributed between moderate and severe drought – which means that 100% of the state is affected by some level of drought.

Increased need for evaporation has exacerbated the dryness of the vegetation, which has enabled more wildfires this year. Active fires such as The Windy Fire and KNP Complex fires were among those that continued to consume dehydrated vegetation in California.

Maps of the American West show a large portion of the region with summer evaporation demand among the highest ever

Evaporation demand was the highest ever in parts of northern and central California.

(Paul Duginski / Los Angeles Times)

The areas of unusual and extreme drought in the drought monitoring map follow fairly closely with the pattern where evaporating demand in the state – the measure of a thirsty atmosphere – is the highest recorded for June to August. This ox-blood-colored portion of the map indicates the largest deviations from normal from California summers from 1980 to 2021.

In November, Science Daily quoted Abatzoglou as saying: “Increased evaporation demand with heating allows fuels to stay dry for extended periods. This is a recipe for more active fire seasons. ”

This prediction has been confirmed in the summer of 2021.

In a paper in April 2020 in the journal Science, of which Abatzoglou was one of the authors, the massive, continuing drought hitting the American Southwest is estimated to be 46% more acute due to human-caused climate change.

Another study a few years ago by Abatzoglou and others estimated that the 2012-2014 drought in California was 8% to 27% more severe due to a warming climate.

There have always been cyclical droughts in California and the West, but scientific evidence suggests that man-made climate change is creating a warmer, thirstier atmosphere that sucks moisture out of the landscape.

“The increase in the need for evaporation is akin to putting an extra straw in one’s drink,” Abatzoglou said. “It’s now much easier to empty the cup.”

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