Comparison of various methods for estimating reference crop evapotranspiration (original) (raw)

The reference crop evapotranspiration (ETo) was estimated for three locations of Bangladesh using the standard Penman-Monteith (P-M) method as recommended by the Food and Agriculture Organization of the United Nations (FAO). The same was also estimated using four other emperical methods and compared with the standard method. The regression equations developed were evaluated with independent data sets. The superiority order were found as: FAO temperature, Radiation, Hargreaves and pan evaporation, respectively. lt is revealed from the study that the regression equation developed herein with FAO temperature method can be used to estimate ETo more accurately than the original FAO temperature method, as well as regression equations with other methods. lntroduction Management practices for optimal utilization of water have been increasingly emphasized because of unevenly distributed rainfall, high evapotranspiration and excessive depletion of groundwater resources. Thus practical methods for the accurate estimation of water use in irrigated agriculture are essential. The estimation of crop water requirement is one of the principal steps in the planning, design and operation of irrigation and water resources systems. Crop water requirements vary with crop characteristics and local condition. Relationships between the evapotranspiration of a pre-selected crop (the reference crop), which is referred to as reference evapotranspiration (ETo), and other crops are established by multiplying ETo by crop coefficients. The ETs depends on local meteorological conditions, whereas the actual evapotranspiration (ET) of a crop depends on its characteristics, time of planting or sowing and stage of crop development.