Potential annual (January-December) and summertime (June-August) regional time trends and increasingly extreme and / or variable values of Palmer-based drought indices were investigated over the contiguous United States (US) between 1895 and the present. Although there has been no significant change in the annual or summertime Palmer Drought Severity Index (PDSI), Palmer Hydrological Drought Index (PHDI), or Palmer Modified Drought Index (PMDI) for the contiguous US over this time frame, there is clear evidence of decreasing drought conditions in the eastern US (northeast, east north central, central, and southeast climate zones) and increasing drought conditions in the west climate region (California and Nevada). No significant time trends were found in the annual or summertime PDSI, PHDI, and PMDI for the spring and winter wheat belts and the cotton belt. The corn and soybean belts have significant increasing trends in both the annual and summertime PDSI, PHDI, and PMDI, indicating a tendency towards reduced drought conditions over time. Clear trends exist toward increasingly extreme (dry or wet) annual PDSI, PHDI, and PMDI values in the northeast, east north central, central, northwest, and west climate regions. The northeast, northwest, and west climate zones display significant temporal trends for increasingly extreme PDSI, PHDI, and PMDI values during the summertime. Trends toward increasingly variable annual and summertime drought index values are also apparent in the northeast, southwest, northwest, and west climate zones.
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[v1] 2012-12-27 21:30:35
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