Deep drought and the first heat waves are preparing the western half of the United States for a hot, dry summer.
Approximately 91% of the west were in drought on June 22nd and 55% experienced extreme or extraordinary drought, while two consecutive heat waves exacerbated the desiccation of soils and vegetation and increased the potential for forest fires. Meanwhile, water supplies are dwindling: Lake Mead, the reservoir formed by the Hoover Dam, is the lowest since the 1930s when it was first filled, and California’s reservoirs are 50% lower than what is usual for this time of year, according to The Associated Press.
The current conditions are part of a 22-year drought in the western United States that had not occurred for more than 400 years before 2000. However, this summer is likely to dwarf the drought of the past two decades. said Benjamin Cook, a climate scientist at NASA’s Goddard Institute for Space Studies.
“Even in the context of the last 20 years of drought, this year really stands out,” Cook told Live Science. “For the southwest, it is very likely the worst drought year since 2002.”
In the short term, the drought in the west is fueled by La Niña conditions that lasted through the winter of 2020-2021, according to Scott Handel, a meteorologist with the National Oceanic and Atmospheric Administration (NOAA). During La Niña, surface temperatures in the eastern Pacific Ocean are cooler than usual, which tends to favor drier weather in the west. This natural variation in Pacific temperatures is now in a neutral state (neither La Niña nor El Niño), Handel told reporters on June 17, and is a reversal in El Niño conditions that bring more moisture to the southwest in winter unlikely. .
Prolonged Drought Is Part of Western US History Modern weather records in the west go back just over a century, but tree rings have a longer record of wet and dry years. These data, some of which are 2000 years old, show that long and deep droughts occur even without the influence of climate change. The period between 800 and 1500 in particular was marked by several persistent droughts. The dry spell that most closely approximates the current 22-year period occurred in the 16th century and eventually lasted 30 years, said Park Williams, a UCLA bioclimatologist. A less severe drought in the 13th century lasted an entire century.
The current drought does justice to these “mega-droughts” of the past, but is exacerbated by climate change. Over the past seven decades, soil moisture has tended to decrease progressively on hotter days in the Southwest, according to a study published on 17. The top 5% of hottest days in the Southwest are 22% drier today than they were in the 1970s, according to the study, and the situation is worse in California and Nevada, where they are 30% drier. This drought is due to decreased humidity in winter and spring, study author Karen McKinnon, a climate scientist at UCLA, told Live Science.
Climate change is causing western states to experience more winter rainfall than rain rather than snow, while warmer spring temperatures lead to more evaporation and transpiration or an earlier loss of surface moisture to the atmosphere. This decrease in snow and spring moisture slows the flow rate of the river in spring and summer.
And those changes affect themselves, said Connie Woodhouse, a paleoclimatologist at the University of Arizona who studies previous electricity flows. Several consecutive years of drought lead to particularly dry soils that absorb water that would otherwise end up in rivers and reservoirs.
“Much of the snow when it melted didn’t go into rivers but to replenish moisture in the soil,” Woodhouse told Live Science.
A feedback loop connects drought, arid soils and heat waves. In humid conditions, solar energy is used to heat and evaporate water before the air temperature begins to rise. In drier conditions, where that energy has nowhere to go, temperatures rise rapidly. With the right weather conditions, such as a high pressure ridge that occurs in the week of Jan.
In addition to all of this, Williams said, an already drought-prone region has been pushed to its limits by the impact of climate change.
“According to our calculations, we would still be in a crisis if we eliminated the global warming trend