Initial Assessment of Global Terrestrial Evaporation Datasets Developed for the GEWEX LandFlux Initiative

Comprehensive documentation of the terrestrial water cycle at the global scale and its evolution over time is fundamental to understanding Earth's climate system and assessing the impacts due to climate change. Such documentation is also needed to characterize the memories, pathways and feedbacks between key water, energy and biogeochemical cycles. GEWEX's long-term scientific goal is to obtain a quantitative description of weather-scale variations in the global energy and water cycles over a period of at least 20 years, which will provide the needed scientific basis for understanding climate variability and change. The LandFlux initiative of GEWEX's Data and Assessment Panel is developing long-term (~1984 – 2009) global data sets of the surface terrestrial heat fluxes (latent, sensible and ground heat) consistent with the GEWEX surface radiation radiation products. Three challenges will be presented in developing the LandFlux data sets: (1) the challenge of developing consistent, long-term inputs needed by the retrieval models; (2) the uncertainty in the estimated fluxes from various models, even when using the same input data; and (3) the challenge of validating the data sets due to the lack of reference observations. Three initial global latent heat (evapotranspiration) data sets developed at Princeton University will be assessed using a global set (>200) FluxNet tower datasets, terrestrial and atmospheric budget analysis over a global set of large river basins and continental regions.