Assessing spatiotemporal variability of drought trend in Iran using RDI index

Drought is one of the natural phenomena which occurs in all climates in different parts of the world. Iran is located in the dry belt of the world. The increase of desertification, drought reoccurrence, and destruction by human in this geographical region needs more studies on spatial and temporal trend of rainfall. In this study, trends of climatic drought during 1975-76/ 2004-05 in seasonal and yearly time scales were evaluated at 50 synoptic stations in Iran using a drought index, RDI (Reconnaissance Drought Index), and Mann-Kendall non-parametric test, at 90 and 95% confidence levels. Results showed that among studied stations, in which RDI was calculated for, 89% had an ascending trend, and results of Mann-Kendall non-parametric test on annual values of RDI showed that among 21 stations, 76% of them had a negative trend and 24% had a significant positive trend. Based on results of this study, there exists an increasing drought trend at all-time scales in Iran.