Comparative Evaluation of Different Reference Evapotranspiration Estimation Methods for Lakhimpur District of Assam, India

Evapotranspiration is very important component of hydrology, crop-water requirements and necessary step in water resources management. In May (1990), Food and Agricultural Organization (FAO) in FAO Irrigation and Drainage Paper No.56 recommended the adoption of FAO-56 PM as a new standard method for estimating reference evapotranspiration that can easily derived from commonly measured data. Nine popular methods such as Blaney-Criddle (BCM), Thornthwaite (THM), Christiansen (CSM), Hargreaves (HGM), Modified Penman (MPM), Priestley-Taylor (PTM), Jensen-Haise (JHM), Makkink (MKM) and Turc (TCM) are considered. Observations recorded at North Lakhimpur Meteorological Station (Assam) are used to calculate the ETO by the selected methods and results obtained are compared with the standard method on monthly and seasonal basis. The comparative evaluation of error and regression analysis results indicate that HGM performed best with lowest RMSE (0.898), MAE (0.804)& (R2=0.7485) followed by BCM with under estimating MBE values on monthly basis. On seasonal basis with lowest RMSE& MAE value, THM is found to be the best for monsoon, MPM for post-monsoon, MPM& PTM for winter and BCM for summer. The MBE values of BCM are underestimated during all four season. The next best methods after FAO-56 PM obtained can be used as guideline for selection of alternative/less data required methods in case of non-availability of data.