SPATIAL COMPARABILITY OF THE PALMER DROUGHT SEVERITY INDEX¹

Abstract

The Palmer Drought Severity Index, which is intended to be of reasonable comparable local significance both in space and time, has been extensively used as a measure of drought for both agricultural and water resource management. This study examines the spatial comparability of Palmer's (1965) definition of severe and extreme drought. Index values have been computed for 1035 sites with at least 60 years of record that are scattered across the contiguous United States, and quantile values corresponding to a specified index value were calculated for given months and then mapped.The analyses show that severe or extreme droughts, as defined by Palmer (1965), are not spatially comparable in terms of identifying rare events. The wide variation across the country in the frequency of occurrence of Palmer's (1965) extreme droughts reflects the differences in the variability of precipitation, as well as the average amount of precipitation. It is recommended first, that a drought index be developed which considers both variability and averages; and second, that water resource managers and planners define a drought in terms of an index value that corresponds to the expected quantile (return period) of the event.(KEY TERMS: drought indices; climatology; water management.)

An aggregate drought index: Assessing drought severity based on fluctuations in the hydrologic cycle and surface water storage

“…It should be stressed that a perfect corroboration was neither anticipated or desired. As mentioned in section 1, the PDSI suffers from certain limitations, primarily geographic biases, inadequate treatment of snowfall, and a complex, empirical formulation [Alley, 1984;Guttman et al, 1992;Keyantash and Dracup, 2002]. Consequently, although the PDSI is a widely used index, it should not be considered as the ultimate standard.…”

“…However, the PDSI is recognized to have limitations owing to its complex, empirical derivation and the fact that its underlying computation is based on the climates of Midwestern states. For a thorough discussion of these weaknesses, refer to Guttman et al [1992], Alley [1984], and Keyantash and Dracup [2002].…”

The response of agricultural drought to meteorological drought and the influencing factors: A case study in the Wei River Basin, China

“…It incorporates antecedent and current moisture supply and demands into a hydrologic accounting system, including a twolayer bucket-type model for soil moisture computation. It has been widely used to reflect agricultural drought due to its close link with soil moisture (Guttman et al, 1992;Dai et al, 2004;Dai, 2010). Calculation of PDSI starts with the determination of monthly departure of moisture from normal by evaluating the differences between precipitation and actual precipitation (Dai, 2011).…”

Development of a remotely sensing seasonal vegetation‐based Palmer Drought Severity Index and its application of global drought monitoring over 1982–2011

“…Although Palmer [1965] attempted to develop a drought index that could be compared among different locations and seasons of a year, the empirical constants used in the original PDSI model were calculated from nine climatic divisions located in the Midwestern United States. This limits its spatial comparability [Alley, 1984;Karl, 1986;Guttman et al, 1992;Wells et al, 2004] and even leads to unrealistic results when the PDSI is applied beyond these conditions not found in these nine regions [Palmer, 1965].…”

“…Alley [1984] noted concerns about modeling soil moisture, runoff, actual evapotranspiration on a monthly temporal scale including neglect of seasonal or interannual changes in vegetation cover and root development, and of the effects of snowmelt or frozen ground. Calibration coefficients and the temperature-alone-based Thornthwaite potential evaporation (1948) formula have also been questioned [Karl, 1986;Guttman et al, 1992;Sheffield et al, 2012]. Although Palmer [1965] attempted to develop a drought index that could be compared among different locations and seasons of a year, the empirical constants used in the original PDSI model were calculated from nine climatic divisions located in the Midwestern United States.…”