چکیده:
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.
خلاصه ماشینی:
Khalilia a Irrigation and Reclamation Engineering Department, University of Tehran, Iran Received: 23 February 2013; Received in revised form: 6 August 2013; Accepted: 9 September 2013 Abstract The present study examined year-to-year variations in areas affected by drought during a period of 39 water years in Iran.
As do other countries located in arid and semi-arid regions, Iran faces a naturally dearth of precipitation in some years that becomes critical at times of severe drought.
The present study used SIAP to monitor meteorological drought in Iran and applied WMA to map SIAP across Iran for each year.
Figure 1 shows the number of stations at which precipitation was measured for water years for 1951-2003.
1. On-site analysis of drought The SIAP calculations were done using the water year precipitation data from 1965 to 2003 from 95 synoptic weather stations.
Figure 5 shows the geographical distribution of drought frequency for severe, moderate, and mild drought and normal conditions for SIAP in Iran.
Geographical distribution of drought frequency for severe, moderate, and mild categories along with normal category of SIAP in Iran 3.
The areas affected by both drought and wet periods by water year are shown in Table 2.
Figure 8(a) shows that a drought entered the country from the northwest and northeast in water year 1995-1996.