Evaluation of global observations-based evapotranspiration datasets and IPCC AR4 simulations

Abstract

[1] Quantification of global land evapotranspiration (ET) has long been associated with large uncertainties due to the lack of reference observations. Several recently developed products now provide the capacity to estimate ET at global scales. These products, partly based on observational data, include satellite-based products, land surface model (LSM) simulations, atmospheric reanalysis output, estimates based on empirical upscaling of eddycovariance flux measurements, and atmospheric water balance datasets. The LandFlux-EVAL project aims to evaluate and compare these newly developed datasets. Additionally, an evaluation of IPCC AR4 global climate model (GCM) simulations is presented, providing an assessment of their capacity to reproduce flux behavior relative to the observations-based products. Though differently constrained with observations, the analyzed reference datasets display similar large-scale ET patterns. ET from the IPCC AR4 simulations was significantly smaller than that from the other products for India (up to 1 mm/d) and parts of eastern South America, and larger in the western USA, Australia and China. The inter-product variance is lower across the IPCC AR4 simulations than across the reference datasets in several regions, which indicates that uncertainties may be underestimated in the IPCC AR4 models due to shared biases of these simulations. Citation: Mueller, B., et al. (2011), Evaluation of global observations-based evapotranspiration datasets and IPCC AR4 simulations, Geophys. Res. Lett., 38, L06402,

Spatial variation in annual actual evapotranspiration of terrestrial ecosystems in China: Results from eddy covariance measurements

“…Although the spatial patterns described by different models generally agreed well with each other for a given region (Mueller et al, 2011;Liu et al, 2013a), large obvious uncertainties in AET values still remain. For example, the mean AET in China estimated by Boreal Ecosystem Productivity Simulator (BEPS) model (369.8 mm yr -1 ) (Liu et al, 2013a) was approximately 26% smaller than the value estimated by Remote Sensing-Penman Monteith model (500 mm yr -1 ) (Li et al, 2014).…”

Water security, global change and land–atmosphere feedbacks

“…Estimates of global average land evapotranspiration range between 1.1 and 2.0 mm d −1 , with an ensemble mean of approximately 1.5 mm d −1 . Thus, there is considerable variability both within the observationally based estimates and between these estimates model-based reanalyses, and Intergovernmental Panel on Climate Change (IPCC) AR4 climate simulations [18]. The best estimates of evapotranspiration are made using eddy covariance techniques, but these are available only at a limited set of stations.…”

The WACMOS-ET project – Part 2: Evaluation of global terrestrial evaporation data sets

“…Despite the recent initiatives dedicated to exploring these evaporation data sets -LandFlux-EVAL in particular Mueller et al (2011Mueller et al ( , 2013 -the relative merits of each model on the global scale remain largely unexplored. To date, the lack of inter-model consistency in the choice of forcing data has hampered the attribution of the observed skill of each evaporation data set to differences in the models.…”