CONTEMPORARY DROUGHT MONITORING WITH THE STANDARDIZED PRECIPITATION INDEX: EVALUATING THE EFFECT OF NONSTATIONARY PRECIPITATION REGIMES IN THE CONTIGUOUS UNITED STATES ON THE CHARACTERIZATION OF DROUGHT

Abstract

This dissertation examines the impact of shifting climatic conditions on the accuracy and reliability of drought characterization in the contiguous United States using the Standardized Precipitation Index (SPI). Each chapter employs climate divisional precipitation data from the U.S. Climate Divisional Database to investigate the dynamics of drought and pluvial events using various 30- to 60-year climatological reference periods. Chapter 2 investigates discrepancies found in NOAA's Climate Divisional SPI Dataset, revealing significant over- and underestimations of drought frequency, suggesting the presence of bias towards drought or pluvial conditions in certain regions. Chapter 3 explores how the choice of climatological reference period influences the SPI's characterization of drought and pluvial occurrence and severity, highlighting the sensitivity of drought indices to their underlying climatological reference periods. Chapter 4 expands on the operational drought monitoring implications of transitioning between reference periods with differing precipitation regimes. Through comprehensive analyses and comparisons against various climatological reference periods, this dissertation uncovers critical insights into the SPI's performance and its dependence on precipitation regimes. The results of this dissertation emphasize the need for adaptive strategies in drought monitoring against the backdrop of a changing climate.