Spatial patterns of drought frequency and duration in the contiguous USA based on multiple drought event definitions

Abstract

This study examines patterns of drought frequency and duration in the contiguous USA based on multiple definitions of drought events. Patterns are examined using data from the three Palmer indices: monthly moisture anomaly index (ZINX), drought severity index (PDSI), and hydrologic drought index (PHDI). The data span a 94-year period and are spatially aggregated to the climatic division level. The stimulus for this study is the lack of systematic examination of the possibility of varying spatial patterns of drought frequency and duration among the drought types represented by these indices.Isoline maps of mean drought frequency indicate that the index used to define a drought has a major impact on the spatial patterns. Patterns identified using the monthly moisture anomaly index are nearly inverse of those for the drought severity and hydrologic drought indices. Patterns of drought duration also vary among the indices, although previous findings of greater drought persistence in the interior regions of the USA were upheld by all three indices. Results also indicate that varying the parameters (intensity, minimum duration) of an index-specific drought event definition has a minor impact only on the spatial patterns.

Characteristics of US drought and pluvials from a high‐resolution spatial dataset

“…The 1-and 3-month SPI indices (Figure 9(a) and (b)) agree with previous studies showing drought occurrence less dominant on the coasts and more dominant in interior United States. (Soulé, 1992). The states in central United States have the highest values with counts of over 40 and 50 years or greater than 40 to 50% of the time, gradually decreasing in occurrence toward the coasts.…”

“…Some basic attributes of anomalous precipitation based on the high-resolution dataset using various timescales and thresholds for definitions of anomalous precipitation are summarized in Table V. This table is an expansion of the one provided by Soulé (1992) that presented results on drought characteristics using Palmer indices. The mean total number of anomalous precipitation events is the average number of events for every PRISM grid point in the United States.…”

“…Lower thresholds have a greater percent of time in an anomalous precipitation event. Soulé (1992) determined that, since the different Palmer values have different timescales, it is possible for an area to have near normal agricultural productivity, while at the same time experiencing a major hydrological or meteorological drought. This is because the shorter timescale droughts such as agricultural PDSI often have one or more months of normal or above-normal precipitation during a longerterm hydrologic drought.…”

“…This was also seen with the time series of drought areas ( Figure 5) where the shorter timescales would have numerous peaks over the same time period as one wider peak in the longer timescales. Soulé (1992) also states that there should be a negative relationship between the number of droughts and duration. An increase in duration would reduce the opportunity for new drought or wet events to be recorded.…”

“…The basis for much of this analysis is from Soulé (1992); however, attention here is given to greater spatial resolution, a number of different indices and a focus on both positive and negative precipitation anomalies. Two index types will be used -the PDSI (Palmer, 1965) and the standardized precipitation index (McKee et al, 1993).…”