PALEOHYDROLOGY OF THE SALINAS RIVER, CALIFORNIA, RECONSTRUCTED FROM BLUE OAK TREE RINGS

The Salinas River is the principal drainage of the south Coast Ranges of California. The lower Salinas valley is an important agricultural region facing severe groundwater depletion and salt water intrusion due to heavy withdraw for irrigation and municipal use. Groundwater recharge is driven primarily by winter precipitation and surface water infiltration. A 60-year record of estimated full natural monthly stream flow is available at Paso Robles in the upper basin, which exhibits dramatic inter-annual to decadal variability, including the epic drought of 1976-1977. Old growth blue oak (Quercus douglasii) woodland is widely distributed in and near the drainage basin of the Salinas River and the radial growth of this species is remarkably sensitive to annual precipitation totals. A new network of 500-year long blue oak tree-ring chronologies has recently been developed. These exceptional proxy time series are highly correlated with annual stream flow at Paso Robles and at other gauging stations along the river. A reconstruction of annual stream flow in the Salinas River indicates several single year stream flow deficits that equal or exceed the drought of 1976-1977, and extreme decade-long droughts more severe than any measured during the instrumental period from 1940-present. The prolonged dryness from 1571-1585 in the Salinas River occurred during the late 16th century megadrought across North America. A drought of this magnitude has important implications to agricultural and hydrological management in the drainage basin.