title: Evidence for increasingly variable Palmer Drought Severity Index in the United States since 1895.
abstract: Annual and summertime trends towards increasingly variable values of the Palmer Drought Severity Index (PDSI) over a sub-decadal period (five years) were investigated within the contiguous United States between 1895 and the present. For the contiguous United States as a whole, there is a significant increasing trend in the five-year running minimum-maximum ranges for the annual PDSI (aPDSI5 yr(min|max, range)). During this time frame, the average aPDSI5 yr(min|max, range) has increased by about one full unit, indicating a substantial increase in drought variability over short time scales across the United States. The end members of the running aPDSI5 yr(min|max, range) highlight even more rapid changes in the drought index variability within the past 120 years. This increasing variability in the aPDSI5 yr(min|max, range) is driven primarily by changes taking place in the Pacific and Atlantic Ocean coastal climate regions, climate regions which collectively comprise one-third the area of the contiguous United States. Similar trends were found for the annual and summertime Palmer Hydrological Drought Index (PHDI), the Palmer Modified Drought Index (PMDI), and the Palmer Z Index (PZI). Overall, interannual drought patterns in the contiguous United States are becoming more extreme and difficult to predict, posing a challenge to agricultural and other water-resource related planning efforts.
authors.affiliation: Chemologica Research, 1617-11th Avenue NW, Moose Jaw, Saskatchewan S6H 6M5, Canada. Electronic address: sierra.rayne@alumni.ubc.ca.
authors.forename: Sierra
authors.initials: S
authors.lastname: Rayne
authors.affiliation: Department of Environmental Engineering Technology, Saskatchewan Polytechnic, 600 Saskatchewan Street W, Moose Jaw, Saskatchewan S6H 4R4, Canada.
authors.forename: Kaya
authors.initials: K
authors.lastname: Forest
keywords: Drought; Hydroclimatic variability; Palmer Drought Severity Index; Time trends; United States