Effects of Inconsistency in Drought Event Definitions on Drought Characteristics

Drought, as one of the hazards exacerbated by climate change, has attracted the attention of many scientists. Many drought studies have used different drought event definitions (DEDs). However, little is known about the effects of these definitions on drought characteristics. This study investigated the effects of DEDs on drought characteristics using the standardized precipitation evapotranspiration index (SPEI) in the Upper Pangani Basin in northeast Tanzania. First, rainfall and air temperature data from the Climatic Research Unit database were used to compute the SPEI. Then, four different types of DEDs were used to identify drought events in the SPEI time series. The identified drought events were examined for agreements and correlations using Kappa and Phi coefficients, respectively, and finally characterized. The findings show that different DEDs produced different types and frequencies of drought events. The patterns of drought events for these DEDs had agreements ranging from 52 to 78% and correlations ranging from 79% to 95%. Different DEDs also led to different drought intensities, ranging from mild to extreme, although the overall drought intensities were either mild or moderate. From this study, we can infer that using suitable DEDs is essential for identifying drought events, as they enable accurate comparisons of droughts across regions and periods, consequently reducing errors and biases in evaluating drought hazards.