The effect of meteorological variables such ambient air temperature, relative humidity, solar radiation, wind velocity and vapor pressure deficit on the rate of pan evaporation was examined at different time scales using 5 years (2001–2005) meteorological data at Qena, Upper Egypt. The examination was made at daily, 10-days, monthly and seasonally time scales. An empirical formula has been deduced concerning the interrelation of meteorological variables with pan evaporation rate. Correlation and simple linear regression analysis were used to observe the influence of individual meteorological variables on pan evaporation rate. Vapor pressure deficit was the most influencing parameter on pan evaporation rate, which affected positively. The ambient temperature and solar radiation, also, have a significant role on evaporation rate, indicating the positive relation while, the wind speed has a less effect. On the other hand, relative humidity has a negative effect. Good agreement between measured and calculated values of pan evaporation rate has been found. It gives us an impression that the derived formula is successful and useful to calculate the evaporation rate in our location.
Pan evaporation, meteorological variables, correlation coefficient linear regression
