Comparison of riparian evapotranspiration estimates based on a water balance approach and sap flow measurements

Estimates of evapotranspiration (ET) from riparian vegetation along a 122 m reach of the San Pedro River using both a water balance approach and by scaling up sap flow measurements are compared. A sensitivity analysis was performed on the components of the water balance to assess the effects of measurement errors on estimates of ET using this method. It was concluded that by reducing the error in three key components to less than 5%, riparian ET could be estimated to an accuracy of 20–25% using the water balance method. The analysis also indicated that random measurement errors up to 10% in the water balance measurements would explain the difference between the water balance and sap flow ET estimates. Demonstrating agreement given reasonable error bounds provides confidence in the accuracy of both methods.