Identifying agricultural drought trends using RDI and eRDI indices in a hot and dry climate

Among the various environmental stresses and hazards, drought is recognized as the most important environmental factor, which is the main challenge in different parts of the world, especially in the Middle East, in addition to widespread effects on agricultural production and productivity, effects on the other social and economic dimensions of humans. Therefore, drought analysis, monitoring, and characterization are one of the main necessities of drought management and planning. In this study, the trend of agricultural drought in the Gonabad region was identified and evaluated by the Reconnaissance Drought Index (RDI) and its improved version, the effective Reconnaissance Drought Index (eRDI) for 59 years (1982-1920). The results showed that there was no significant difference between the indices, although the eRDI index was more sensitive and accurate in seasonal periods. The longest drought period was obtained for 9 years through the eRDI FAO index and the longest wet period was calculated for 11 years by all indices. Also, the highest frequency of weather conditions was related to the normal situation (33.9 to 39%). On a seasonal scale, the longest droughts and wet periods were calculated in spring for 8 and 6 years, respectively. These conditions were 7 and 6 years for autumn and 9 and 7 years for winter, respectively. All indicators identified wet conditions for the summer. In general, although the eRDI index can be more efficient in determining and monitoring the agricultural drought due to the use of effective precipitation instead of cumulative rainfall, in this study no significant difference was observed between the two indicators. Therefore, seems that the RDI index can be used in drought monitoring and analysis in climatic regions similar to the study area.