Comparison of Different Models in Estimating Standard Evapotranspiration in Lampung Province, Indonesia

Evapotranspiration (ET) is the loss of water to the atmosphere by combined processes of evaporation from soil and plant surfaces and transpiration from plants. Since various factors affect ET, including weather, crops and soil parameters; numerous equations have been developed to quantify standard ET. The equations vary in data requirements from very simple, empirically based or simplified equations to complex, more physically based equations. This study used six methods in estimating standard evapotranspiration using data from September 2011‒August 2012 from Climate Station at Masgar (05o10'20” S, 105o10' 49”E, 50 m dpl) Lampung, Indonesia. The six models are: Hargreaves-Samani 1985 (H/S), FAO 24 Radiation (24RD), FAO 24 Blaney-Criddle (24BC), FAO 24 Pan Evaporation (24PAN), Linacre (Lina), and Makkink (Makk). The results were analyzed using statistics methods in error indicators, which are: Root Mean Square Error(RMSE), Mean Absolute Error (MAE), and Logaritmic Root Mean Square Error(LOG RMSE), while the closeness among the models was analyzed using Index Agreement (IA). Direct measurement had been done using lysimeters (3x2x1) m. The study concluded that Makkink model is the suitable simple model that should be chosen in Lampung lowland area to calculate ETo when climate data is limited, besides the recommended FAO 56 Penman Monteith.