Almost half of the United States is currently experiencing some level of drought, and it is expected to worsen in upcoming months. Experts say the dry conditions could put a strain on water supplies and have important effects on the environment, such as increasing susceptibility to fire this summer.
The map above, built with data from the U.S. Drought Monitor, depicts areas of drought in the continental U.S. on March 23, 2021. It is based on measurements of climate, soil, and water conditions from more than 350 federal, state, and local observers around the country. NASA provides experimental measurements and models to this monitoring effort.
The hardest hit areas are in Arizona, Utah, Nevada, Colorado, and New Mexico, where severe to exceptional drought developed in 2020 and persisted through winter. A weak summer monsoon season and ongoing La Niña conditions have stifled precipitation. La Niña is characterized by cooler than normal sea-surface temperatures in the central and eastern tropical Pacific Ocean. The associated weather patterns can push the jet stream north and cause it to curve, diverting storms and precipitation away from the region.
The map below shows surface soil moisture as of March 29, 2021, as measured by the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) satellites. The colors depict the wetness percentile; that is, how the levels of soil moisture compare to long-term records for the month. Blue areas have more abundant water than usual, and orange and red areas have less. The darkest reds represent dry conditions that should occur only 2 percent of the time (about once every 50 years).
In California, many of the state’s reservoirs are currently below historical averages due to an absence of strong winter storms and below-average snowpack in the Sierra Nevada. As of March 2, the state closed out its fifth consecutive month with below-average rain and snow.
The current event fits the pattern of a long megadrought episode over the past two decades. A recent study showed 2000-2018 has been the driest period in the U.S. Southwest since the late 1500s.
“The larger megadrought and this event are certainly not independent of one another,” said Andrew Badger, an author of the study and researcher at NASA’s Goddard Space Flight Center. “While the megadrought period is primarily focused on the southwest U.S., the current drought outlook also has a larger spatial extent as it extends farther east towards the Great Plains.”
The map below shows shallow groundwater storage as of March 29, 2021, as measured by the GRACE-FO satellites. The colors depict how the amount of groundwater compares to long-term records (1948-2010). Groundwater in aquifers is an important resource for crop irrigation and drinking water, and it also can sustain streams during dry periods. Groundwater takes months to rebound from drought, though, as it has to be slowly and steadily replenished by surface moisture that seeps down through soil and rock to the water table.
The National Oceanic and Atmospheric Administration (NOAA) announced in its spring outlook that warmer-than-average temperatures this spring, below-average precipitation, and low soil moisture could lead drought conditions to expand in the Great Plains and southern Florida. Winter wheat crops already took a hit from a severe cold outbreak in February.
“As with any extreme event, pinning down the root causes can be challenging. The important thing to remember is the underlying conditions of the megadrought that are present now were present for the 2012-2013 drought,” said Badger. “These conditions can prime the surface for drought events to become more extreme when the right atmospheric conditions arise.”
NASA Earth Observatory images by Lauren Dauphin, using GRACE data from the National Drought Mitigation Center and data from the United States Drought Monitor at the University of Nebraska-Lincoln. Story by Kasha Patel.