Abstract:
Land evapotranspiration is an essential component of the climate system, but has been long linked with uncertainties in most regions of the world due to a lack of ref- erence global observations. This has important consequences for climate research and hydrology. Land evapotranspiration constitutes one of the missing terms of the global water cycle. Moreover, land-atmosphere exchanges have been shown to strongly impact climate-change projections, in particular with regard to changes in climate variability and extreme events.

Several recently developed datasets based in part on observations, now provide global evapotranspiration estimates: dedicated satellite-derived products, observation-driven land surface model simulations, reanalysis data products, and datasets based on atmo- spheric water balance estimates. The LandFlux-EVAL initiative, which is part of the LandFlux activity spearheaded by the GEWEX radiation panel, aims at evaluating and inter-comparing these new datasets. In this presentation, the rationale and plans for the LandFlux-EVAL initiative will be highlighted, together with 〉st results from on-going investigations and their implications.