This chapter describes analyses of the variability and characteristics of drought for historical and future projected climate conditions across the Western United States. The analyses are performed using the Palmer Drought Severity Index (PDSI; Palmer, 1965) to define drought events. The advantage of using PDSI to define droughts is that it focuses explicitly on droughts driven by hydroclimate variability. The PDSI does not include anthropogenic effects, such as water management, including the effects of reservoirs and diversions. Thus, PDSI is well-suited to examine natural climate-driven drought characteristics (i.e., drought duration, severity, and frequency).
The next section (Section 4.1) describes the PDSI dataset and how it is used in the analyses. Section 4.2 describes the methodologies used to identify and analyze drought events. Section 4.3 presents results, along with considerations regarding the interpretations of the results. Summary and next steps emerging from the analyses are described in Section 4.4. Lastly, a listing of key findings is given in Section 4.5.
