Ph.D. Dissertation Abstract by Ze'ev Gedalof (2002)

This thesis is composed of three principal chapters, each describing a distinct line of inquiry:

1. Five paleoproxy reconstructions of Pacific Basin climatic variability are examined in order to identify the extent to which these records provide a coherent signal. A composite chronology of these records is well correlated with the Pacific Decadal Oscillation (PDO) index, and provides a better record of PDO variability than any of the constituent chronologies back to 1840. This record suggests that the PDO may not have been an important organizing structure in the North Pacific climate system over much of the 19th century.

2. Empirical Orthogonal Function (EOF) analysis is used to identify patterns in annual area burned by wildfire in the American Northwest. Extreme wildfire years are forced in part by antecedent drought and summertime blocking in the 500 hPa height field. However the response to these events is modulated by the ecology of the underlying forest. At more mesic forest types antecedent drought preconditions forests to burn, but is not a good predictor of area burned due to the rarity of subsequent ignition. At especially dry locations, blocking events alone can lead to increases in area burned even in the absence of antecedent drought. Summertime cyclones can also lead to increased area burned, probably due to dry lightning storms that bring ignition and strong winds but little precipitation. Management paradigms that rely on fuel treatments alone to eliminate large, intense fires are consequently unlikely to succeed.

3. A network of drought sensitive tree-ring chronologies is used to reconstruct flow on the Columbia River at The Dalles, Oregon, since 1750. Residual statistics from this model exhibit a positive trend over time, indicating a change in the relationship between drought and streamflow caused by changes in land use over the twentieth century. The multiyear drought of the 1930s was the second most severe on record, with a more intense drought occurring during the 1840s. The period from 1950 to 1987 is unique in the last 250 years with respect to the relative absence of multiyear droughts.