Factual Drought Index (FDI): a composite index based on precipitation and evapotranspiration
V. Fassouli, Christos A. Karavitis, Demetrios E. Tsesmelis, Stavros Alexandris
Abstract
Droughts are mainly caused by rainfall deficiencies and high evapotranspiration rates. This article introduces a Factual Drought Index (FDI) as a composite index, based on precipitation and potential evapotranspiration (PET). Its innovation lies in the fact that it does not consider the total PET, but only the amount of PET that exceeds or falls behind the corresponding average PET, for a certain time period. So far, the PET-based indices take into account the total amount of PET, which in semiarid areas, may lead to overestimation of drought events. FDI was tested in drought-prone Greece, for the year 1990, when the country experienced an extreme drought event, and its results were compared to the corresponding Standardized Precipitation Index (SPI) and Standardized Precipitation Evapotranspiration Index (SPEI). FDI constitutes a useful drought-management tool, as it satisfactorily identifies and categorizes drought events and is sensitive to precipitation and evapotranspiration changes.