Estimation of reference Evapotranspiration, the best pan coefficient and rice plant coefficient using the pan evaporation data in rice growth period ;Case study: Mordab plain region in Guilan province, Iran

Pan Evaporation is a good index for estimating reference evapotranspiration (ETo) and finally irrigation requirement of rice plant. Application of Pan Evaporation is an appropriate method for estimation of evapotranspiration Because of simplicity and ease of data interpretation and also precision in humid zones. Pan coefficient is used to estimate reference evaporation values from pan evaporation data. In condition of no accessibility to reliable data, the Fao-Penman-Monteith (F-P-M) is a standard method for evaluation of results of other experimental methods. This research was conducted in 2010 on Mordab plain region (Guilan province) with utilization of farm evaporation pan data. Pan evaporation was calculated and then with computing of Kpan by using of different equations like Cuenka, Allen and Pruitt, Snyder, modified-Snyder and Orang .The reference evapotranspiration calculated by the multiplication of Epan and Kpan. The statistics researches and regression studies shows that for estimation of daily ETo and also 10 days ETo in the studied area is proper to apply the Snyder and modified-Snyder and Cuenka methods. The most appropriate pan evaporation coefficient is calculated using the Snyder method. Also values of rice plant coefficient for 10 days period was calculated from the beginning of transplant to the end of rice growth period.

Evapotranspiration Class A pan Kpan Rice