The effect of PET method on Reconnaissance Drought Index (RDI) calculation

Drought severity is conventionally assessed by drought indices. Several drought indices with varying complexity have been used in many geographical areas. Recently, a powerful drought index, the Reconnaissance Drought Index (RDI), is gaining wide acceptance mainly in the arid and semiarid climatic regions. Since RDI is based both on precipitation and potential evapotranspiration (PET), it is interesting to assess the effect of the PET calculation method on the drought severity characterisation obtained by RDI. This paper compares the results of RDI for various reference periods using some popular empirical PET methods with minimum data requirements. The selected methods are: Hargreaves, Thornthwaite, Blaney–Criddle and FAO Penman–Monteith (only temperature). The FAO Penman–Monteith method is used as reference method. The data used are from meteorological stations in Greece representing the mountainous and the coastal Mediterranean climatic conditions. No significant influence on RDI was detected by using the selected PET methods. However, the Hargreaves and FAO P–M (only T) methods performed relatively better. This supports the opinion that RDI is a robust drought index, not dependent upon the PET calculation method.

► RDI is a drought index incorporating precipitation and potential evapotranspiration. ► The dependence of PET method on drought characterisation by RDI is studied. ► Four PET methods were tested against Penman–Monteith method for calculating RDI. ► No significant influence was detected in RDI for various selected reference periods. ► For simplicity reasons temperature based PET methods could be used in RDI calculation.