Temporal and spatial evaluation of evapotranspiration methods for estimating potential evapotranspiration in Arid and Semiarid regions

摘要

Potential evapotranspiration (PET) is an important index of hydrologic budgets at different spatial scales and is a critical variable for understanding regional biological processes. In this research, four PET calculating methods were evaluated usingdata from nineteen meteorological stations in Fars Province in Iran. The evaluated methods include as: original Hargreaves method (OH), a new method based on monthly temperature and rainfall (MH), the original Thornthwaite method (OT) and modified Thornthwaite method (MT). The main objective of this study is to evaluate estimated PET by these methods against the estimated corresponding values using the standardized FAO-56 Penman-Monteith (PM) method. The monthly PET values have teen calculated by abovementioned methods, then were compared with FAO-56 PM. Spatial distribution maps of the best method were prepared based on monthly calculated PET values in PM method and by using the geographical coordinate of the stations in monthly and yearly scales. Inorder to finding the appropriate methods in different months or season of the year, temporal analysis were done and the results show that, the OH method in the Winter and Spring Seasons, by contrast the MH method for the warm months and MT method in some months of the year, such as October to February were appropriate. The OT was weakest method for Fars Province. Also in determine the best method in yearly scale inside Fars Province; the results showed the OH method for arid climate and MH method for semi-arid were appropriate.