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The daily climatic data employed in this study were composed of: minimum air temperature (Tmin), maximum air temperature (Tmax), wind speed (U2), relative humidity (RH), and solar radiation (Rs). The data were divided into two sets: the data from June 1, 2009 to December 31, 2010, 549 records (about 60% of total data), were used for training the models, and the remaining 365 records from January 1, 2011 to December 31, 2011 (about 40%) were used for testing. A full year data set used in the identification period enabled inclusion of various hydrological conditions that are observable during different seasons of the year. In this way the model became robust for the different hydrological conditions that prevail in the total time series (Kişi 2006). The statistical parameters of daily climatic data are shown in Table 1. The minimum and maximum values of ET0 used in the training periods ranged from 0.01 to 4.60 mm; however, the maximum value of the testing periods’ ET0 is 5.11 mm, which may cause difficulties in estimating the high ET0 values.

Table 1

Statistical parameters of climatic data and the PMF-56 ET0 in each data set

Climatic data and the PMF-56 ET0MinimumMaximumMeanStdSK
Tmin (°C) 
 All −24.70 15.90 −2.89 9.63 −0.22 
 Training −23.60 15.90 −2.53 9.45 −0.15 
 Testing −24.70 13.10 −3.43 9.88 −0.30 
Tmax (°C) 
 All −21.00 29.00 7.98 10.60 −0.26 
 Training −21.00 28.20 8.28 10.40 −0.23 
 Testing −17.90 29.00 7.52 10.90 −0.29 
RH (%) 
 All 18.52 98.10 59.59 18.94 0.11 
 Training 19.75 98.10 61.30 18.49 0.06 
 Testing 18.52 97.49 57.01 19.33 0.22 
U2 (m s−1
 All 0.46 2.08 1.16 0.26 0.07 
 Training 0.47 2.08 1.15 0.26 0.15 
 Testing 0.46 2.02 1.16 0.27 −0.05 
Rs (MJ m−2 day−1
 All 0.00 12.59 4.50 3.48 0.43 
 Training 0.00 12.59 4.39 3.50 0.47 
 Testing 0.00 12.06 4.65 3.45 0.37 
PMF-56 ET0 (mm day−1
 All 0.01 5.11 1.44 1.25 0.73 
 Training 0.01 4.60 1.39 1.23 0.69 
 Testing 0.01 5.11 1.51 1.28 0.77 
Climatic data and the PMF-56 ET0MinimumMaximumMeanStdSK
Tmin (°C) 
 All −24.70 15.90 −2.89 9.63 −0.22 
 Training −23.60 15.90 −2.53 9.45 −0.15 
 Testing −24.70 13.10 −3.43 9.88 −0.30 
Tmax (°C) 
 All −21.00 29.00 7.98 10.60 −0.26 
 Training −21.00 28.20 8.28 10.40 −0.23 
 Testing −17.90 29.00 7.52 10.90 −0.29 
RH (%) 
 All 18.52 98.10 59.59 18.94 0.11 
 Training 19.75 98.10 61.30 18.49 0.06 
 Testing 18.52 97.49 57.01 19.33 0.22 
U2 (m s−1
 All 0.46 2.08 1.16 0.26 0.07 
 Training 0.47 2.08 1.15 0.26 0.15 
 Testing 0.46 2.02 1.16 0.27 −0.05 
Rs (MJ m−2 day−1
 All 0.00 12.59 4.50 3.48 0.43 
 Training 0.00 12.59 4.39 3.50 0.47 
 Testing 0.00 12.06 4.65 3.45 0.37 
PMF-56 ET0 (mm day−1
 All 0.01 5.11 1.44 1.25 0.73 
 Training 0.01 4.60 1.39 1.23 0.69 
 Testing 0.01 5.11 1.51 1.28 0.77 

Std, standard deviation; SK, skewness.

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