Bias in Drought Severity Resulting from Fixed Thresholds

Keywords: Drought, Hydroclimatology
Session Type: Virtual Paper Abstract
Day: Sunday
Session Start / End Time: 2/27/2022 08:00 AM (Eastern Time (US & Canada)) - 2/27/2022 09:20 AM (Eastern Time (US & Canada))
Room: Virtual 47

Abstract

Drought monitoring systems utilize operational definitions to quantify the onset, severity and termination of each drought event using fixed thresholds for drought classification. However, when fixed thresholds are applied across CONUS, they can lead to biases in assessing the spatial and temporal variations and trends in drought frequency and severity. This study uses a suite of drought indices and indicators to quantify the biases associated with fixed drought severity thresholds. A drought climatology is first developed for each drought index and indicator across CONUS. This climatology quantifies the drought frequency in each drought severity category based on the operational definitions used by the United Stated Drought Monitor (USDM). Results show many circumstances where the observed drought frequencies do not align with the recurrence intervals associated with the USDM categories. Thus, objectively defined drought thresholds which vary and depend only on the period of record for a given location are compared to fixed thresholds. Results show that these objectively defined thresholds vary as a function of climate region, season, and type of drought. A comparison of fixed and objectively defined severity thresholds allows us to quantify the classification bias in some of the commonly used drought indices and indicators. The results of this research provide a versatile method for enhancing the accuracy of drought frequency and severity assessments across CONUS and can be used to better monitor trends in drought characteristics.