differentiation of computed sum of hourly and daily reference evapotranspiration in a semi-arid climate

Electronic weather stations have increased the availability of weather data for computing hourly and daily reference evapotranspiration (eto). there is a rational question applied for different climate conditions whether the sum of hourly eto computation may differ from direct computed daily eto. in this study for the kerman area, daily and hourly reference crop water consumption were estimated by the penman-monteith equation, using meteorological data collected in one hour intervals by an automatic weather station at iranian academic center for education, culture and research (acecr), kerman city, iran. the direct computed daily evapotranspiration values were compared with the sum of hourly computed evapotranspiration values. results indicated that there is a distinctive difference between the values as calculated for this experimental station. based on two tail 95% level t-test, the direct computed daily eto was greater than the sum of hourly computed eto. finally, the relationship of daily and sum of hourly eto for the study area were presented which can be utilized to compare and convert the computed values.