Wind-adjusted Turc equation for estimating reference evapotranspiration at humid European locations

Abstract

The Turc equation is one of the simplest empirical equations used for estimating reference evapotranspiration (ET0) under humid conditions. However, this equation generally overestimates ET0 values at windless humid locations and underestimates ET0 at windy humid locations. The main objective of this study is to develop a new adjusted Turc equation through introduction of the wind adjustment factor. In this study, data from CLIMWAT database have been divided into two groups in order to verify the model on half of the dataset. As the mean monthly data from CLIMWAT refer to the long-term average year, the detailed Western Balkans (WB) dataset with the monthly data from real years has been used for additional verification of the wind adjustment factor. For each verification station, ET0 estimates from the original and adjusted Turc equations have been statistically compared with FAO-56 Penman–Monteith (PM) ET0 estimates. The adjusted Turc equation provides good agreement with the evapotranspiration, and produces a reliable estimation at all locations. These results support the use of the adjusted Turc equation for estimating reference evapotranspiration at European humid locations where humidity data are not available.