Methods to separate observed global evapotranspiration into the interception, transpiration and soil surface evaporation components

Evaporation is made up of three components: interception, soil surface evaporation and transpiration. They each have different stores of water and different characteristic timescales. It would be useful to be able to identify the relative proportions of these components at large, even global, scales for land surface model validation. The possibility of separating out the components of observed evaporation at large scales is reviewed with reference to methods used at local scales, landscape scales and scales used in remote sensing. Many of the traditional methods used require intensive measurement programmes and are unlikely to be practical at large scales. New techniques using time-series analysis may be used to deliver a global three-component evaporation product.