On Monday, a paper was published in the journal Nature Climate Change, in which scientists estimated that the amount of snow in Sierra Nevada Mountains has touched the lowest mark in over past 500 years.

Senior study author Valerie Trouet, a paleoclimatologist at the University of Arizona, said they were expecting that 2015 would be extreme, but not to this extent.

The report is the latest in a number of studies done to characterize the depth of California's four-year drought and place it in a broader historic context. It has joined the growing body of research warning that global warming is going to decrease the amount of snow blanketing California mountains. If this happens, the state's available water will be reduced as its population is also increasing at a fast pace.

Mark Gold, associate vice chancellor for environment and sustainability at the University of California, Los Angeles, said, “This is probably the biggest water supply concern our state is facing. On a scale of one to 10, it's 11”. He was not involved in the new study.

According to UC Davis hydrology expert Helen Dahlke, the problem is that with climate change there is going to be much less snow and more rain.

Dahlke was not a member of Trouet's study team. He said water will keep on flowing into the ocean until a way is found to capture some of that water quickly.

Snowpack is a main factor in water supply in California. Melting Sierra Nevada snow gives the state one-third of its water in a normal year. Another third is taken out from underground aquifers, and the rest belongs to rivers and reservoirs.