Korean Journal of Soil Science and Fertilizer ISSN:0367-6315(Print) 2288-2162(Online) 한국토양비료학회 학회지

Reference evapotranspiration (ET₀) can be estimated using Hargreaves equation with temperature data alone. The equation has a tendency to overestimate for regions of high relative humidity and to underestimate for regions of wind speed greater than 3 m s^-1. The study was conducted to determine Hargreaves equation coefficient in 11 regions in Gangwondo by comparing ET₀ determined by modified Hargreaves equation with ET₀ by the FAO Penman-Monteith equation. The Penman-Monteith ET₀ values were determined using the weather data including solar duration, air temperature, humidity, and wind speed for 11 weather stations in Gangwondo from 2007 to 2017. The modified Hargreaves coefficients for inland regions such as Chuncheon, Hongcheon, Cheorwon, Wonju, Inje, Yeongwol, Daegwallyeong, and Taebaek ranged from 0.00181 to 0.00199, less than the default value 0.0023. The modified coefficients for coastal regions such as Gangneung, Sokcho, and Donghae ranged from 0.00275 to 0.00302, greater than the default value. Modified Hargreaves ET₀ using modified coefficients reduced root mean square error (RMSE) from 0.84 mm d^-1 to 0.69 mm d^-1 and increased Nash-Sutcliffe coefficient (NSC) from 0.69 to 0.78 compared with original Hargreaves ET₀. Therefore the modified Hargreaves coefficients obtained from the study can provide more accurate ET₀ estimates than using original default value by considering regional climate characteristics in Gangwondo.

Modified Hargreaves coefficient for 11 regions in Gangwondo.