Tree-ring reconstructed hydroclimate of the Upper Klamath Basin

This work presents the first tree-ring reconstructions of the Upper Klamath basin hydroclimate, which extends through northern California and southern Oregon. The extended record provides a centuries-long perspective on the hydroclimatic variability in this region, which is in a transitional zone with respect to the western U.S. precipitation dipole. It also can provide a long-term hydroclimatic context to the political issues which have erupted in the basin in recent years. Reconstructions of water year precipitation for Klamath Falls (extending 1564 - 2004 and 1000 - 2010 CE) were developed to identify and compare past drought intensities with droughts of the instrumental record. The reconstructions suggest that variability exhibited during the instrumental period captures moderate-to-long duration (six-, ten-, and twenty-year average) droughts, but it is likely that short (one- and three-year average) and very long (fifty-year average) dry periods are more intense during the eleventh-through-thirteenth century. The late-sixteenth century "mega drought", noted throughout western North America, is also present in the Klamath basin, though with less strength than in the neighboring Sacramento River reconstruction. Cool-season storm tracks appear to be a direct driver of hydroclimatic variability, leading to instances of see-saw like transitions with neighboring regions, such as in the mid-fourteenth century. In contrast, the larger area of drought in the eleventh century is suggestive of a long-term northward shift in cool-season storm tracks.