California has long been suffering from drought. However, a recent paper published in the journal Nature Climate Change reveals just how historic and potentially devastating the effects of this dry spell have become.

The amount of snow in the Sierra Nevada has reached its lowest level in 500 years. Currently, it is at five percent of the average annual level.

The initial aim of the study was to better understand the extent of four-years of drought in California. What it found was that the amount of snow in the mountains may be permanently reduced- forever restricting the state’s water supply.

“We were expecting that 2015 would be extreme, but not like this,” said the study’s author Valerie Trouet, a paleoclimatologist from the University of Arizona.

The snow of the Sierra Nevada mountains is key to the amount of water available in California. As the snow melts and run downstream, it fills rivers and reservoirs. Ultimately, one third of the state’s water supply comes from this snowpack.

“This is probably the biggest water supply concern our state is facing,” said Mark Gold, associate vice chancellor for environment and sustainability at UCLA. “On a scale of 1 to 10, it’s 11.”

The knowledge of Sierra Nevada’s role in California’s well being is not new. Since the 1930s, snow levels have been closely monitored. 108 measuring stations are established throughout the mountain chain.

In order to determine the snow conditions for the past hundreds of years, the team of researchers examined tree rings to see earlier conditions.

“What we know about snow and how it varies from year to year is that there are two important climatic factors that play a role,” said Trouet. “One of them is the amount of precipitation that falls and the other is the temperature at the time that precipitation falls. With higher temperatures your precipitation is going to fall as rain.”

2015 saw winter temperatures that were the highest ever recorded in California. This is possibly the result of the building El Nino weather pattern. Scientists predict this will lead to less snow and more rain.

Although this may sound like an ideal answer to a prolonged draught, ground conditions are currently in such a dire state that the water will be unable to be absorbed. Rather, the runoff will build, causing floods and mudslides, before eventually returning to the ocean.

“That water will just be going into the ocean unless we can figure out a way to capture some of that water quickly,” said Helen Dahlke, a hydrology expert from UC Davis.

Climate conditions are naturally cyclical. However, global warming specialists are worried that thanks to increased green house gases, a return to the good old days may be impossible.

“With anthropogenic warming, those high temperatures are going to be rising,” said Trouet. “We can assume that the return interval is going to get shorter.”