محاسبه ميزان فرابرآورد تبخير- تعرق مرجع با استفاده از داده هاي ايستگاه هاي هواشناسي غيرمرجع در ايران

Adjusting the Amount of Overestimation Reference Evapotranspiration Calculated by Non Reference Data in Iran

Irrigated crop is the main component of Iranian agriculture and 93% of the total extractable water resources is used in this sector. In general, water requirements of field crops is estimated by FAO-Penman-Montieth method based on the data collected from well-irrigated stations (reference stations). However, most of the climatological stations are not located in places where irrigation is practiced and therefore, the use of this data causes an overestimation of reference evapo transpiration. The purpose of the present study was to survey these overestimations after correction according to temperature data nationwide. Data from 153 synoptic stations was used and amount of annual and seasonal overestimation was calculated. Results showed that overestimation was as large as 68% for Spring-Summer in central and west regions and 65% for Autumn-Winter season in central and southeastern regions. This value for annual evapotranspiration was 410/0 in southeastern regions.