Comparison of Hydrological and Meteorological Drought Monitoring using RDI and EDI Indices

Drought is a natural event that causes water deficit in many countries every year. Arid and semi-arid climate and inappropriate distribution of rain in terms of spatially and temporally has caused doubled increase of negative effects of water deficit in Iran. It is necessary to study drought phenomenon in order to plan and manage encountering with this phenomenon. In this research, the meteorological and hydrological drought situation of Doroud-Boroujerd basin was investigated using data from five meteorological stations and three hydrometric stations from 1987 to 2016. For this purpose, EDI drought meteorological index and RDI drought hydrological index with threshold discharges of Q70 and Q90 were used. The daily precipitation data were used to calculate EDI index and daily discharge data were used to determine RDI index. The results were assessed and compared on annual, monthly and regional scale. The results indicated the prevalence of normal and moderate droughts in most areas of the basin. Moreover, it was found that the EDI index is less sensitive to the length of the statistical period and has logical time changes; hence, it has the capability required for use in drought monitoring system. This index determined 2012 as the driest year. In addition, RDI index showed 1991 as the driest year in both discharge cases, Q70 and Q90 threshold.