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The measurement of reference evapotranspiration has a critical role in planning and managing water resources. There exist several methods to estimate this phenomenon, viz, radiation, temperature, mass transfer, pan evaporation and combination-based methods. This study was conducted with the aim to test the accuracy and suitability of nine pan evaporation-based methods under the prevailing climatic conditions of Tandojam, Sindh, Pakistan. Twenty-three years data were used and the pan evaporation based methods were evaluated against Penman-Monteith method. The results showed that only the Pereira method gave good results (BIAS=0.06; Nash Sutcliffe model efficiency=0.87) among the nine-pan evaporation based methods. The rest of the methods deviated from the reference method. Thus, Pereira is recommended to be employed in lieu of the Penman Monteith method when the complete meteorological data set is unavailable. The other methods tested in this study must be calibrated before use.
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