After years of intense, record-setting drought across the U.S., particularly in the Great Plains and California, the country is now experiencing its lowest level of drought in the 17 years since the U.S. Drought Monitor began its weekly updates.
Less than 5 percent of the U.S. was in some stage of drought as of May 4, the most recent update, compared to the 65 percent mired in drought in September 2012.
“I have been an author of the U.S. Drought Monitor since 2005 and we have had very few instances where there was so little drought, and to see the changes we have in the last year, especially out West, it does astonish me,” Brian Fuchs, of the U.S. Drought Mitigation Center, said in an email.
The last time drought levels across the country were this low was in July 2010, when 8 percent of the U.S. was in drought — then came a remarkable period of deep, damaging drought that led to billions in crop and livestock losses, spurred major water restrictions, and helped fuel terrible wildfires.
The ups and downs in drought could be linked to some of Earth’s natural climate cycles that can usher in relatively wet and dry periods. But climate change is likely to play a role — and probably already has — as higher temperatures lead to increased evaporation and therefore worse drought conditions.
The epicenters of drought were in the central and southern Plains states from 2011 to 2013 and California from 2012 to this winter. At the peak of its drought, more than half of California was experiencing “exceptional” drought conditions, the highest category. At the end of September 2011, more than 85 percent of Texas was in this category.
Both droughts were fueled by a combination of dry weather and repeated, sizzling heat waves. The exceptional heat that blanketed much of the central and eastern portions of the country in 2012 boosted it to the hottest year on record for the U.S., while California experienced back-to-back record-hot years during its drought.
That heat is probably the clearest link between climate change and droughts, as rising global temperatures fueled by increasing concentrations of greenhouse gases in the atmosphere tilt the odds in favor of record heat and away from record cold.
Studies have pointed to the role of climate change-fueled heat in California’s drought, and droughts in the future, no matter where they happen in the U.S., are likely to be more intense than those of today because temperatures will be higher on average.
Less clear, though, is how climate change might impact the atmospheric patterns that can lead to prolonged dry periods. During California’s drought, a persistent area of high pressure kept storms from bringing rains and snow to the parched state. While research has suggested this has been happening more often, it’s unclear if the reason is linked to global warming.
Perhaps the clearest regional signals of climate change increasing drought are in the already arid Southwest, where droughts are expected to happen more often, last longer and be more intense than in the past. There is also some suggestion of more consecutive dry days for the Southern Plains, which could make it easier for that region to tip into drought.
And for the West Coast — which depends on its winter snowpack to provide meltwater that keeps reservoirs topped up through the dry summer months — warming could mean more water falls as rain instead of snow, throwing a wrench in the current water storage systems and making dry summer conditions more likely.
The warming climate will also interact with Earth’s natural climate cycles, such as the El Niño-La Niña seesaw that can lead to wetter or drier conditions in parts of the country, as well as longer-lasting cycles like the Pacific Decadal Oscillation and Atlantic Multidecadal Oscillation.
It is a recent switch in the phases of these two cycles that may have tipped the country from deep drought to normal conditions, said Victor Murphy, climate services program manager for the National Weather Service’s Southern Region. Studies have shown, he said, that certain phases of these cycles are connected to larger drought footprints in the U.S. and the opposite phases to less drought.
For the time being, overall drought levels in the U.S. are likely to hover around the current level, Fuchs said. Some areas, such as Florida, are likely to come out of drought as the summer wet season kicks in. Others, such as Georgia and parts of Texas, may see drought develop or deepen in the coming weeks.