HR: 15:20h
AN: GC52A-07 INVITED     [PDF]
TI: Quantifying Hydrologic Drought in the Sierra Nevada With Tree Rings: A Frequency-dependent Approach
AU: * Meko, D M
EM: dmeko@LTRR.arizona.edu
AF: University of Arizona, Laboratory of Tree-Ring Research West Stadium University of Arizona, Tucson, AZ 85721 United States
AB: Tree-ring reconstructions for the Sierra Nevada suggest that extended droughts uncharacteristic of the instrumental period occurred more than 500 years ago. Were comparable droughts to occur today, they would likely stress water supplies in even those large basins where reservoir storage serves as a buffer against climate fluctuations. The reconstructed severity and duration of such droughts depends critically on the low-frequency runoff signal in tree rings. Yet in the Sierra Nevada, the low-frequency component of tree growth is sometimes disparate in different species, and even in different chronologies of the same species. Moreover, a sharp increase in tree-ring index over the last 100 years is present in many chronologies yet absent from the observed streamflow records. To address these discrepancies, a frequency-dependent approach to reconstruction is proposed. The main difference from the conventional reconstruction approach is filtering to separate the high-frequency and low-frequency components prior to reconstruction. Different subsets of chronologies may be selected as predictors for the two components, depending on their correlation with streamflow at the high and low frequencies. PCA is incorporated to condense the frequency-dependent variance common to multiple chronologies. The method is illustrated in a reconstruction of annual flow of the San Joaquin River, California, and results are compared with those of a more conventional reconstruction. Ranking of tree-ring chronologies by relative strength of runoff signal was found to differ markedly in the high and low frequencies. Reconstructions by the two methods are similar for the 20th century calibration period, but differ greatly at times in the distant past. For example, the frequency-dependent approach accentuates the severity of a drought in the early 1300s and the magnitude of a shift from dry to wet conditions near A.D. 1600. The method may be useful in posing alternative scenarios of severe sustained drought consistent with variations in tree growth.
DE: 1812 Drought
DE: 1833 Hydroclimatology
DE: 1860 Runoff and streamflow
DE: 3344 Paleoclimatology
SC: Global Climate Change [GC]
MN: 2003 Fall Meeting