Earth and Planetary Sciences ETDs


Lindsay Ross

Publication Date



A detailed history of drought variability in the Colorado River Basin for the last half millennium was obtained using tree ring-widths of precipitation sensitive trees as a proxy record of past climatic conditions. A one-dimensional edge detection filter was applied to standardized ring-width indices to identify years with rapid change in ring-width magnitude that may reflect changes in state. Both standardized indices and edge detection outputs were mapped to analyze how the spatial pattern of drought changes over time. A Principal Components Analysis was performed for both the mapped index and edge detection outputs to determine whether there were specific patterns within the data. This data analysis identified repeating spatial patterns between each of the identified drought periods during drought onset, with the first principal component of the edge detection accounting for 60% of the variance in the edge data. A temporal mapping of principal component loadings suggests that the Pacific Decadal Oscillation and the Atlantic Multidecadal Oscillation play a significant role in forcing drought onset patterns. Superposed Epoch Analysis and a species-sensitivity analysis revealed that there are differences that exist between the droughts, including variation in the timing of the peak index year relative to the onset of drought (peak edge year), in magnitude of drought response, and in the migration patterns of drought onset, making it difficult to classify the droughts. The edge detection filter was found to be successful in identifying periods of drought onset, illustrating drought onset, and capturing migration of drought areas. The Principal Component Analysis loading patterns suggest that there are specific regions within the Colorado River Basin that vary synchronously during drought onset. Having a better understanding of these repeating regional variations in the Colorado River Basin will lead to improved drought predictability, and aid in water management in the region.

Degree Name

Earth and Planetary Sciences

Level of Degree


Department Name

Department of Earth and Planetary Sciences

First Committee Member (Chair)

Fawcett, Peter

Second Committee Member

Gutzler, David




drought, Colorado River Basin, edge detection filter

Document Type