Drought Assessment Using RDI Index in Iran
Drought is one of the natural phenomena which occur in all climates in different parts of the earth. Iran is located on the dry belt of the world. Because of increasing the human desertification and drought events, more and appropriate studies of spatial and temporal trend of rainfall as the most important hydrologic variable are needed in this country. At the present study, by considering various criteria like length of recorded data, less missing data and suitable spatial distribution, meteorological drought trends in seasonal and yearly time series was evaluated at 50 synoptic stations in Iran. The spatiotemporal trend was assessed using reconnaissance drought index (RDI) and Mann-Kendall non-parametric test at 90 and 95% confidence limits. Results of RDI showed an ascending trend of 89% for 62 seasons and the 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. The results of the study showed that there is an ascending drought progress at all the time scale in Iran.
Keywords� Climatic Drought, Drought Trend, RDI, Mann�Kendall test, Iran.