Scientists delivered some disheartening California drought news Monday, announcing that the state’s record-low snowpack is the most paltry to fall on the Sierra Nevada mountains in the last 500 years. Not since the 16th century has California’s most sprawling mountain range been so parched, even if an El Niño storm currently drenching parts of the state makes way for more typical weather patterns this winter.

Scientists arrived at the 500-year-low conclusion after conducting two tree-ring studies on several living and dead tree groups. They sought to gauge temperatures and rainfall as far back as the year 1400. Researchers concluded that a snow-drought this calamitous had only a 5 percent chance of emerging in the Sierra Nevada once every 500 years. The unnerving results of the study were published Monday in the journal Nature Climate Change, in a paper that issues a more damaging picture of the state’s five-year drought than previously thought.

The alpine peaks of the Sierra Nevada in 2008

One of the study’s chief researchers, Valerie Trouet, told the LA Times, “We were expecting that 2015 would be extreme, but not like this.”

The plight facing California comes down to the vitality of snowfall: The Sierra Nevada snowpack accounts for a third of the state’s water supply, and as temperatures rise, essential snowfall will turn to rain. In 2015, California experienced a normal amount of precipitation, but this year was also the warmest year on record globally, so what might have been a normal snowpack quickly disintegrated. Much of California’s groundwater supply has also been siphoned up for agriculture.

California Governor Jerry Brown put sharp drought-time legislation into effect in April, and many of the state’s most populous regions, like Los Angeles, have been subjected to regular water-use restrictions.

Photos via Getty