A Comparison of Regional Drought Patterns in the Contiguous United States Using Four Measures of Drought Severity

The primary objectives of this study are 1) to identify spatially homogeneous drought (moisture) regions in the contiguous United States using four different measures of drought severity, and 2) to determine whether these regional drought patterns are consistent across the drought types represented by these indices. Data used include monthly values of the Palmer Hydrologic Drought Index (PHDI)' Palmer Drought Severity Index (PDSI)' Palmer Moisture Anomaly Index (ZINX), and standardized scores (zscores) of precipitation (PREZ), for the period 1931-1985. A series of S-mode principal components analyses and a VARIMAX rotation are used to search for aggregations of climatic divisions that experienced similar drought (moisture) conditions during the study period. Regional similarities among the drought types are greatest in the southeast, middle Atlantic/northeast, Pacific Coast/ northern Intermountain, and southern Pacific Coast regions. The greatest differences in regional drought patterns among the drought types occur in the central United States, particularly those areas with component loadings above 0.70.