Spatial Analysis of Meteorological Drought in Iran from 1965 to2003

The present study examined year-to-year variations in areas affected by drought during a period of 39 water yearsin Iran. Ninety-five meteorological stations were chosen to provide near-continuous long-term records, althoughsome data was missing (less than 10%). The missing data points were estimated using a linear correlation methodbetween the reference station with the missing data points and a neighboring station that had a complete record. At allstations, the standard index of annual precipitation (SIAP) was calculated for water year (sum of precipitation fromOctober 1 to September 31). The geo-statistical method of weighting moving average (WMA) was applied to a 2×2km grid network map of Iran and the geographical distribution of SIAP was calculated and displayed. From this, thepercentage of area affected by severe, moderate, and mild drought was computed for each year; the frequency ofdrought was analyzed by severity and the behaviors of the most extensive historical droughts were determined. Theresults showed that: a) the maximum frequency of severe drought was 5.1 times and moderate drought was 23.1 timesper 100 years; b) the most extensive droughts (more than 80% of the country) occurred during 1970-1971 (82.21%),1988-1989 (92.05%), and 1999-2000 (96.27%); and c) drought spread in Iran beginning from the northwestern andsoutheastern regions, gradually extending to the central regions.