Assessment of Drought and Trends Analysis of Short-Duration Dry Periods in Iranshahr Region, Using a Markov Chain (1980-2006)

Document Type : Original Articles


Department of Physical Geography and Climatology, Faculty of Geography and Environmental Planning, University of Sistan and Baluchestan.


The purpose of this study is to identify the occurrence of drought events and short-term dry periods in Iranshahr region. The standardized precipitation values are applied for detecting drought in Iranshahr region for the period of 1980-2006. For recognition of short duration dry periods, a Markov chain model was used. The daily data were classified into two groups; wet days (precipitation equal or more than 0.1mm) and dry days (precipitation less than 0.1mm). The frequency of wet and dry periods and the probabilities of the duration of each wet and dry period and its return periods were calculated. The analysis of droughts has shown that the frequency of drought periods in the initial years of statistical period is fewer and that they have less regularity. After 1998, not only the drought frequency but also its intensity and duration is increased. The probability of two successive wet or dry days, the differences of simple and climatic probabilities of wet and dry days was determined. The results showing that significant differences do not exist between simple and climatic probabilities of wet and dry short duration periods. The frequency of dry days is observed in all months. The monthly average of dry duration is 25 or more days.