Arizona's ongoing drought can claim another dubious distinction, according to a study by scientists at the Laboratory of Tree-Ring Research at the University of Arizona in Tucson.

The scientists say a recent six-year stretch of below-average river flow, which ended in 2017, was the longest such stretch since the 1300s. Before that recent dry spell, the longest stretch without a year of above-average flow was five years, the Phoenix New Times reported last month.

The LTRR scientists based their study on tree-ring data, using that information to estimate the flow levels of rivers that provide water to the Phoenix area and other parts of Central Arizona.

While the stretch of below-average river flow was broken by a wet winter in 2017, Arizona remains in the throes of a 21-year period of abnormally precipitation. That's expected to continue for several years, and it could soon trigger a reduction of water allocations to the state from Lake Mead — which currently is at 39 percent of capacity, the New Times reported.