Potential evaporation at eddy-covariance sites across the globe

Abstract

Abstract. Potential evaporation (Ep) is a crucial variable for hydrological forecast and in drought monitoring systems. However, multiple interpretations of Ep exist, and these reflect a diverse range of methods to calculateEp. As such, a comparison of the performance of these methods against field observations in different global ecosystems is badly needed. In this study, we used eddy-covariance measurements from 107 sites of the FLUXNET2015 database, covering 11 different biomes, to parameterize and compare the main Ep methods and 10 uncover their relative performance. For each site, we extracted the days for which ecosystems are unstressed based on both an energy balance approach and on a soil water content approach. The evaporation measurements during these days were used as reference to validate the different methods to estimate Ep. Our results indicate that a simple radiation-driven method calibrated per biome consistently performed best, with a mean correlation of 0.93, an unbiased RMSE of 0.56 mm day -1, and a bias of -0.02 mm day -1 against in situ measurements of unstressed 15 evaporation. A Priestley and Taylor method, calibrated per biome, performed just slightly worse, yet substantially and consistently better than more complex Penman, Penman-Monteith-based or temperature-based approaches.We show that the poor performance of Penman-Monteith based approaches relates largely to the fact that the unstressed stomatal conductance was assumed constant. Further analysis showed that the biome-specific parameters required for the simple radiation-driven methods are relatively constant per biome. This makes this 20 simple radiation-driven method calibrated per biome a robust method that can be incorporated into models for improving our understanding of the impact of global warming on future global water use and demand, drought severity and ecosystem productivity.

Assessing regional drought impacts on vegetation and evapotranspiration: a case study in Guanacaste, Costa Rica

“…For each site, Maes et al. () extracted the days for which ecosystems are unstressed based on both an energy balance approach and on a soil water content approach. The validation of the 15 PET estimation methods used the unstressed days as the ground truth to reference.…”

“…Potential evapotranspiration. -Maes et al (2018) compare the performance of the 15 most common methods for computing PET. The study used eddy covariance measurements from 107 sites of the 10 FLUXNET2015 database, covering 11 different biomes, to parameterize and compare these methods and uncover their relative performance.…”

“…The study used eddy covariance measurements from 107 sites of the 10 FLUXNET2015 database, covering 11 different biomes, to parameterize and compare these methods and uncover their relative performance. For each site, Maes et al (2018) extracted the days for which ecosystems are unstressed based on both an energy balance approach and on a soil water content approach. The validation of the 15 PET estimation methods used the unstressed days as the ground truth to reference.…”

Satellite observed solar induced fluorescence to monitor global plant stress

“…Data from the FLUXNET2015 archive (http://fluxnet.fluxdata.org/data/fluxnet2015-dataset/) is used to create an in situ evaporative stress validation dataset [12]. Stress is defined as the ratio of Ea to Ep (same as Eq.…”

“…Stress is defined as the ratio of Ea to Ep (same as Eq. 1) for flux towers where Ep is estimated by a subset of unstressed days as outlined in Maes et al [12]. After masking for rain and snow using daily data from Multi-Source WeightedEnsemble Precipitation (MSWEP v2.0) [20] and the European Space Agency (ESA) GLOBSNOW product [21], a minimum of 100 flux tower observations are required for each tower to remain in the comparison.…”