Estimation of Reference Evapotranspiration Using Full and Limited Data of Sari, Qarakheil and Amol Synoptic Stations

Unfortunately, at some meteorological stations, there are no facilities for measurement of some weather parameters, so, they should be estimated. Therefore, determining the correctness of the reference evapotranspiration (ETo) method by using the estimated data is very important. Based on this, the objective of the present study was to evaluate the performance of the Penman-Monteith method for estimating ETo in Mazandaran Province, Iran, when solar radiation (Rs), vapor pressure (ed) and relative humidity (RH) data are not available. Data of Sari, Qarakheil, and Amol synoptic stations were used to compare the estimated ETo by the Penman-Monteith method for the complete and limited data sets. The results showed that when RH and ed data were missing, the Penman-Monteith method was still a very good option for estimating ETo in Sari, Ghaemshahr and Amol station, with RMSE values smaller than 0.3 mm day-1. However, when Rs was missing, the Penman-Monteith method was not good enough for estimating ETo, and RMSE increased to more than 1 mm day-1. The results also showed that solar radiation was the most effective parameter on ETo estimation and both vapor pressure and relative humidity had the same effect on ETo estimation.