Khanikar, P. G.Sharma, Saurabh2020-06-082020-06-082019-07http://krishikosh.egranth.ac.in/handle/1/5810147312Pan coefficient is an important parameter for computation of reference crop evapotranspiration (ETo) from pan evaporation (Epan). In this study the five empiricalapproaches proposed by Snyder (1992), Cuenca (1989), Orang (1998), Allen and Pruit (1991), Pereira et al. (1995) were used to estimate pan coefficient (Kpe) by using weather parameter of Jorhat over 20 years (1996 to 2016). Kpe values obtained from the empirical methods, on regression did not reveal a good fit line with that of the pan coefficient (PMKp) values calculated from FAO Penman-Monteith method which is considered as one of the most accepted methods worldwide. However Snyder method gave best pan coefficient value among all empirical approaches with coefficient of determination (R2 ) value of 0.16, root mean square error (RMSE) value of 0.35, mean absolute deviation (MAD) value of 0.33, correlation coefficient (r) value of 0.42 and percent error (PE) value of 34.29 on monthly basis. Reference Evapotranspiration (EToe) estimated by multiplying Epan values by Kpe values obtained by empirical methods were compared with the reference evapotranspiration values estimated by Penman-Monteith method (PM ETo). On comparison of EToe values from all empirical methods with PM ETo values, evaluation statistics revealed that EToe estimated from Snyder method was closer to PMETo, with R2 value of 0.36, RMSE value of 0.71 mm, MAD value of 0.69 mm, r value of 0.57 and PE value of 24.68% on mean monthly data. Hence Snyder method is assumed to be the best method for calculating ETo using pan coefficient and pan evaporation data. The line graphs drawn among daily EToe of all empirical methods and daily PM ETo revealed that EToe from Snyder method was closer to PM ETo than EToe of other empirical methods. Based on visual comparison as well as from statistical criteria EToe computed from Snyder method gave closer agreement with PM ETo for daily and monthly estimates as compared to other approaches. Moreover the model developed (Equation I) between Epan and PM ETo revealed a strong correlation between the two variables with R2value of 0.938. Another model obtained from regression line fitted with mean daily PM ETo on mean daily EToe from Snyder method showeda good correlation between the two variables (Equation II) with coefficient of determination (R2) value of 0.893. ETo estimated by all the three above mentioned approaches viz. Snyder equation, Equation I and Equation II were ultimately validated with PMETo for the mean daily ETo of individual year 2017 and 2018 and pooled data of two years (2017-18) respectively. On comparison of different EToe values with PM ETo values, evaluation statistics revealed that equation II was the best approach among all the three approaches with lowest RMSE, MAD and PE values for all above mentioned time period. With available Kpe data estimated by Snyder method, EToe (Snyder) can easily be estimated by multiplying pan evaporation data and thenmodel II can be used to get better value of reference evapotranspiration. On the other hand reference evapotranspiration can also be estimated with only the available pan evaporation data by equation I for this region.enThesis