Regional Calibration Of Hargreaves-Samani Equaton Based On Temperature And Humudity Data For Aegean And Inland Anatolia Region Of Turkey

Penman-Monteith equation is the most commonly used model in the literature for estimation of reference (grass) evapotranspiration (ET0) because of the fact that it gives more accurate and consistent estimates. Despite its higher accuracy potential, Penman-Monteith equation requires quite a few meteorological quantities as explanatory variables affecting the value of evapotranspiration such as solar radiation, air temperature, wind velocity, and relative humidity. Because it needs so many meteorological variables and partly due to its cumbersome analytical form, the Penman-Monteith equation is not easily applicable for all cases for calculating the reference evapotranspiration, and therefore the Hargreaves-Samani equation is necessarily used instead of it for regions at which the pertinent meteorological data may not be available. In this study, first, Hargreaves-Samani equation is calibrated using maximum temperature, minimum temperature, maximum humidity and minimum humidity data measured at 90 stations in Aegean and Inland Anatolia Region of Turkey. In conclusion, it is observed that the calculated evapotranspiration values using calibrated Hargreaves-Samani equation are close to those calculated by Penman-Monteith equation. The maximum temperatures are observed to be more effective than the other meteorological variables on the evapotranspiration values calculated by the calibrated Hargreaves-Samani equation for crop water requirements in the Aegean Region of Turkey. The minimum humidity are observed to be more effective than the other meteorological variables on the evapotranspiration values calculated by the calibrated Hargreaves-Samani equation in the Inland Anatolia Region of TurkeyKey words: Reference evapotranspiration, calibration, Penman-Monteith, Hargreaves-Samani.