Drought indices are commonly used tools for drought characterisation and analysis. The Reconnaissance Drought Index (RDI) is one of the widely used indices, due to its high sensitivity and resilience. The basic form of the index is the ratio of the cumulative precipitation to potential evapotranspiration, for a specified reference period. The RDI is also transferred to a normalised and a standardised expression. Since the RDI incorporates both the main input and the main output of a natural water system, it is considered as an appropriate index of water availability. Based on this notion, as shown in recent studies, the RDI is suitable for the assessment of drought impacts on agriculture. In this paper, a modified version of the index, RDIe, is presented, in which precipitation is replaced by the effective precipitation. With the proposed modification, the amount of water beneficially exploited by the agricultural systems can be represented more accurately, enhancing the performance of the index for agricultural drought analysis. Further, alternative ways for the calculation of effective precipitation are presented and discussed. An application of the modified RDI in an agricultural area demonstrates its better performance in assessing the impacts of drought on the rainfed agricultural production