Major Over- and Underestimation of Drought Found in NOAAʼs Climate Divisional SPI Dataset

Drought frequency is being mischaracterized in climate divisions across the United States due to NCEI SPI values using a sliding rather than fixed calibration period. This introduces biases toward drought in the central, Midwest, and Northeast United States and biases away from drought in the western United States, the northern Midwest, and parts of the Southeast and Texas.