study of temperature and radiation based methods of estimating maximum evapotranspiration with different probabilities

abstract in order to estimate the reference evapotranspiration different equation is used. validity of each methods depends upon the climate and the parameters which are used in these equations. therefore it is necessary to calibrate these methods for any specific area and for any desired frequency. in this study common temperature and radiation based methods were used for calculating crop evapotranspiration and the results were compared with standard method of estimating reference evapotranspiration. the results showed that jensen-haise(j-h) method overestimate et compare to hargreaves-samany(h-s) method. the difference is more in 3 days period of irrigation than 5 days period. also for wheat and barely h-s method estimates higher value of etc compared with j-h method. however, j-h method overestimate etc for cotton and rice. by increasing the probability level, the difference between calculated etc by j-h and h-s decreased significantly.