From the half-million acres of parched and idle farmland to the swaths of receding reservoirs, the signs of California's historic drought are obvious.
Less obvious is just how historic the ongoing drought actually is when compared with previous dry spells in the Golden State's history.
A CNBC analysis of annual Palmer Drought Severity Index recordings, founded by meteorologist Wayne Palmer as a way to factor in both precipitation and temperature to track soil moisture, shows the nearly four-year drought is in fact the worst in over a century. The PDSI is used by the National Oceanic and Atmospheric Administration as its main drought index. (Tweet This)