The effect of calculated radiation from Allen model on the rate of change potential evapotranspiration of FAO Penman-Monteith model (Case Study: Yazd Province)

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Abstract

Evapotranspiration is one of the main sources of water loss in arid areas of Iran. There are various methods for assessment of potential evapotranspiration and FAO - Penman Monteith selected as a standard method for estimation of reference evapotranspiration. FAO PM method needs high field data which is sometimes inaccessible in many areas and or is not agreement with extension in area. In addition, data gathering is often expensive and non repeatable, and use this model in some places limited. Given that the net radiation data not be recorded in most stations of Yazd province. In this study, the net radiation data in FAO Penman-Monteith model using maximum and minimum temperature data with experimental relation that proposed by Allen has been, calculated. So the data required for this model is limited to measuring air temperature, relative humidity and wind speed. Also in this study the Priestley Taylor method used for calculating evapotranspiration. However, for the assessment, FAO Penman-Monteith model with all data is considered as a reference. The results show that, when the net radiation is missing, FAO Penman-Monteith method with minimal data can be a suitable method for estimating potential evapotranspiration. So that this method unlike Priestley Taylor method, the correlation coefficient at all studied stations is higher than 0.97 and Root mean square error between is less than 0.37 mm per day. Therefore, the proposed model by Allen in calculating net radiation for the hot and arid province of Yazd is suitable and recommended.

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