Spatial Analysis of Meteorological Drought in Iran from 1965 to2003

Document Type : Research Paper


Irrigation and Reclamation Engineering Department, University of Tehran, Iran


The present study examined year-to-year variations in areas affected by drought during a period of 39 water years
in Iran. Ninety-five meteorological stations were chosen to provide near-continuous long-term records, although
some data was missing (less than 10%). The missing data points were estimated using a linear correlation method
between the reference station with the missing data points and a neighboring station that had a complete record. At all
stations, the standard index of annual precipitation (SIAP) was calculated for water year (sum of precipitation from
October 1 to September 31). The geo-statistical method of weighting moving average (WMA) was applied to a 2×2
km grid network map of Iran and the geographical distribution of SIAP was calculated and displayed. From this, the
percentage of area affected by severe, moderate, and mild drought was computed for each year; the frequency of
drought was analyzed by severity and the behaviors of the most extensive historical droughts were determined. The
results showed that: a) the maximum frequency of severe drought was 5.1 times and moderate drought was 23.1 times
per 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 and
southeastern regions, gradually extending to the central regions.