Abstract
Accurate estimate of reference evapotranspiration is essential for water resource and irrigation project planning and operation that include optimal irrigation scheduling. The study was conducted at melkassa the aim of the study was to estimate reference evapotranspiration of Melkassa area using five different empirical models. Evapotranspiration of the crop and reference evapotranspiration are affected by the climatic parameters like temperature, sunshine duration, humidity, wind speed, solar radiation and so on. Hence, all available climatic data gathered and the estimation of reference evapotranspiration of the area calculated based on five models used. ETo computed by The Blaney-Criddle method, Modified penman method, Radiation method, Throntwaite method and Hargreaves equation. From the result Thornthwaite method gave the maximum rate of Reference evapotranspiration (264.7 mm/month) which is over estimated. The Blaney-Criddlemethod provided the smallest reference evapotranspiration rate (83.7 mm/month). Moreover, the Modified Penman method showed relatively high estimation next to Thornthwaite method and it consists of the energy (radiation) terms and the aerodynamic (wind speed and relative humidity) terms which increased the method to be suggested for the area. The Radiation method showed better evapotranspiration next to Modified Penman method it is the best alternative in the presence of measured wind speed and air humidity data.
Highlights
Evapotranspiration is the loss of water to the atmosphere by the combined processes of evaporation from the soil and plant surface and transpiration from plants
The analyzed data revealed that Blaney-Criddle method, Modified penman method, Radiation method, Throntwaite method and Hargreaves equation estimated reference evapotranspiration approximately was tabulated as follows
Based on the empirical formula of equation 1 and 2 of the Blaney-Criddle method, climate data including mean monthly temperature, percent of daily sunshine hour and constants obtained based on relative humidity and wind speed from tables, reference evapotranspiration (ETo) forMelkassa area was calculated
Summary
Evapotranspiration is the loss of water to the atmosphere by the combined processes of evaporation from the soil and plant surface and transpiration from plants. Estimation of evapotranspiration is one of the major hydrological components for determining the water budget and is becoming indispensable for the calculation of a reliable recharge and evaporation rate for the groundwater flow analysis. It is reliable and consistent estimate of evapotranspiration is of great importance for the management of water resources efficiently [2]. Evapotranspiration can be determined either by direct method through measurement on field condition or by using models that relates different climatic data and water loss in crop field [14]. This models are empirical formulas which are formulated at different area of the world and can be used anywhere with some limitation since they are formulated with particular climate conditions
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