Reconstructing the Mediaeval low stands of Mono Lake, Sierra Nevada, California, USA

Palaeosimulations of Mono Lake covering the past 2 kyr have been conducted using a water balance model forced with tree-ring derived inflow estimates. The results show two low stands, during the ninth to tenth a rid twelfth to thirteenth centuries, th at agree well in timing a rid magnitude with those described by Stine (1987, 1990, 1994) on the basis of geomorphic evidence and relict trees and shrubs exposed on Mono Lake's artific ially exposed shorelands. The lake simulations provides independent corroboration of the timing and magnitude of Stine's drought-induced low stands and supports the accuracy of tree-ring-derived estimates of Mediaeval precipitation and runoff reductions in the central Sierra Nevada. Specifically, we estimate that during, the two Mediaeval droughts, centennial average precipitation and river runoff in the central Sierra Nevada reached as low as 75% of the twentieth century values, with multidecade averages as low as 60-65%. In both magnitude and duration, these droughts far exceed anything experienced in the region during modern times. An analysis of the spatial patterns of reconstructed drought indices shows that the particular 'two drought' Mono Lake low stand signal was focused over central and southern California, indicating the dominant role of boreal winter precipitation deficits. In this respect, the 'Great Sierra Nevada droughts' were somewhat distinct from the more general Great Basin/far western Plains pattern of Mediaeval aridity over the western USA.