Scientists said climate change because of human activities led to more severe historic drought in California. The climate change made it 15 to 20% worse, they said. Scientists from the University of Idaho, NASA's Goddard Institute for Space Studies and Columbia University's Lamont-Doherty Earth Observatory have come up with the finding.

According to the scientists, natural variations in temperature and rainfall patterns led to the drought. But as temperatures increase as a result of climate change, more rainfall is required for plants, soil, rivers, in order to compensate for the more evaporation because of the rising mercury.

According to lead study author Park Williams, a bioclimatologist at Lamont-Doherty, "A lot of people think that the amount of rain that falls out the sky is the only thing that matters. But warming changes the baseline amount of water that's available to us, because it sends water back into the sky".

It is believed that a ridge of high-pressure air over the northeast Pacific has caused the drought. The ridge is named as 'Ridiculously Resilient Ridge' by a number of scientists for the reason that it is persistent. It is obstructing moisture-laden ocean air from making landfall. The researchers were not sure regarding the exact reason behind the ridge, but a study conducted by Stanford scientists found that climate change could make these conditions frequent.

However, the drought could still be aggravated as a result of warming global temperatures even when the ridge is not led by climate change.