Natural Resources, School of


Date of this Version



Journal of Hydrology 624 (2023) 129917.


Open access.


A recent, two-parameter version of the thermodynamically derived complementary relationship (CR) of evaporation has been tested on a monthly basis at 124 FLUXNET stations around the globe. Local, station-by-station calibration explained 91% (R2) of the variance in eddy-covariance (EC) obtained latent-heat fluxes with the same Nash-Sutcliffe efficiency (NSE) value. When the dimensionless Priestley-Taylor parameter (α) was expressed as a universal function (f) of the estimated wet-environment air temperature (Tw), station-by-station calibration of the single dimensionless parameter, b (accounting for moisture advection), yielded an R2 value of 87% and NSE of 86%. Global calibration (all stations at once) of the two-parameter CR version yielded R2 = 82% and NSE = 81%, while the single-parameter version produced R2 = 81% and NSE = 79%. With a representative value (between the locally calibrated mode and mean) of b set equal to two, the thus, calibration-free CR still maintained an R2 of 80% and NSE of 78%, which is significantly better than Morton’s calibration-free WREVAP model (i.e., 71% and 55%, respectively). The advantage of the current CR model is that it can be employed in a fully calibration-free mode, similar to WREVAP, yet with available EC measurements or water-balance derived latent-heat fluxes the single [b, when α = f(Tw) is chosen] or two parameters (α and b) of the model can be easily calibrated within the respective 1 – 1.32 and 1 – 10 intervals, for further improved performance.