Study of Relative Effectiveness of Climatic Factors on Potential Evapotranspiration Using the Factor Analysis (Case Study: Zanjan and Mahneshan Stations)

In this research relative importance of different meteorological variables that affect potential evapotranspiration were analyzed. Two stations of Zanjan and Mahneshan with at least twenty years of data up to 2021 were selected for the research. The Penman-Monteith method was used to estimate ET0. In order to study the relative importance of climatic variables the factor analysis method was used. The correlation between precipitation, means of air temperature (maximum and minimum), wind velocity, relative humidity and actual sunshine hours were analyzed. Results showed that except one item with no significant correlation (wind and precipitation) all the other correlation coefficients were significant in 5 percent level. In both stations the eigenvalues of the two first factors were greater than one, however, they were negligible (close to zero) in the cases of other factors. In Zanjan the first two factors accounted for about 80.673 percent of total variance. This value was more than 82.5 percent in the case of Mahneshan station. In both stations the actual sunshine hour was the main parameter affected ET0 followed by the Tmax, Tmin and RH positioned in second to fourth ranks. Results indicated that for the selected stations the precipitation had no effect on ET0. Plotting the position of parameters on Cartesian plain showed that the position of parameters in the two stations are similar. The findings of this study are helpful in water resources management in the region.