Comparison of reconnaissance drought index (RDI) and effective reconnaissance drought index (eRDI) to evaluate drought severity

Drought is one of the main natural causes of damages to the ecosystems, agricultural productions, water resources, etc. Many indices have been developed to assess drought severity. Reconnaissance Drought Index (RDI) and Effective Reconnaissance Drought Index (eRDI) are two of the newest indices in drought evaluation. These indices are based on ratio of precipitation and potential evapotranspiration. In this study meteorological data of 22 synoptic stations with different climatic conditions in Iran during 1967-2014 were used to calculate values of RDI and eRDI indices. According to the result of means comparison of RDI and eRDI values, in stations with humid condition such as Ramsar and Bandar Anzali difference of the means between RDI and eRDI indices were not significant at 5% level, but in stations with hyper arid and arid condition such as Chahbahar, Bandar Lengeh, Yazd and Zabol, difference of the means in RDI and eRDI was significant at 5% level. Therefore, it is suggested to replace RDI with eRDI in regions with hyper arid and arid conditions, but in regions with sub-humid and humid conditions because of the similarities between RDI and eRDI, RDI index (without need to calculate the effective rainfall) was used.