Numerous drought indices with various intricacy have been utilised in several climatic regions. Presently, the reconnaissance drought index (RDI), which is considered as a powerful index of meteorological drought, is acquisitioning approval primarily in semi-arid and arid climatologic areas. Because RDI is based on precipitation (P) and evapotranspiration (ET), it assesses the ET estimation effects on the characterisation of drought severity computed by RDI. The current study sheds light on the impact of the ET methods, and the elevation and climate conditions on the RDI annual results, (particularly, the alpha form of the index (RDIα12)), using three of the most widespread experimental ET estimates with low data requirements. These techniques are known as Thornthwaite, Hargreaves, and Blaney-Criddle, and are utilised in addition to the Food and Agriculture Organization Penman-Monteith reference technique. Data from 24 stations for the period from 1979 to 2014 cover different elevations and climatic conditions. No significant (P > 0.05) impacts on both the standardised (RDIst) and normalised (RDIn) forms of the RDI were detected by applying the considered ET methods at various elevations for various climatic conditions. However, the RDIα12 is directly influenced with a significant (P < 0.05) deviation that has been observed by various ET methods at different elevations and climate conditions. Accordingly, consideration should be paid to the ET estimation methodologies, in particular at high elevations. The use of various approaches may lead to flaws in availability of water resources and water quality forecasts.