A Comparison Between Conventional and M5 Model Tree Methods for Converting Pan Evaporation to Reference Evapotranspiration for Semi-Arid Region

In this study, the performance of M5 model tree and conventional method for converting pan evaporation data (E<Subscript>p</Subscript>) to reference evapotranspiration (ET<Subscript>0</Subscript>) were assessed in semi-arid regions. Conventional method uses pan coefficient (K<Subscript>p</Subscript>) as a factor to convert E<Subscript>p</Subscript> to ET<Subscript>0</Subscript>. Two common K<Subscript>p</Subscript> equations for pans with dry fetch (Allen et al. <CitationRef CitationID="CR3">1998</CitationRef>; Abdel-Wahed and Snyder in J Irrig Drain Eng 134(4):425–429, <CitationRef CitationID="CR1">2008</CitationRef>) were considered for the comparison. The values of ET<Subscript>0</Subscript> derived using these three methods were compared to those estimated using the reference FAO Penmane Monteith (FAO-PM) method under semi-arid conditions of the Khuzestan plain (Southwest Iran). The results showed that the M5 model is the best one to estimate ET<Subscript>0</Subscript> over test sites (0.5 mm d<Superscript>−1</Superscript> of root mean square error (RMSE) and 0.98 of coefficient of determination (R <Superscript>2</Superscript>). Conversely, the performance of the two K<Subscript>p</Subscript> equations was poor. Copyright Springer Science+Business Media Dordrecht 2013