Abstract ID: 43

A new method to directly observe the evaporation of intercepted water over an Eastern Amazon old-growth rain forest

Conventional methods of estimating rainfall interception have yielded a wide range of results for tropical rain forests, with interception estimates ranging from 8 to nearly 40% of total annual precipitation. There are now many more long-term eddy flux measurement sites than sites at which the individual forest water budget components (total precipitation, throughfall, and stemflow) are measured. It is worthwhile to pursue a method for estimating interception using eddy-covariance data from the flux sites. We introduce and demonstrate a new method to measure the interception evaporation over an old-growth rain forest in the eastern Amazon using eddy covariance that could be applied to other flux tower sites worldwide in varying forest types. The approach is to estimate the 'excess' evaporation that occurs following individual events, using baseline evaporation time series obtained from long time series of flux data and creating ensemble averages from these precipitation events and base-state dry days. One advantage of this method over the traditional techniques of estimating interception using rain gauges alone is that the interception evaporation is directly measured and not determined as the residual of incident precipitation and throughfall. Furthermore, the large differences in interception that can occur on a site due to varying forest canopy density, structure and the appearance of canopy gaps is smoothed out using the eddy covariance method as the size of the flux footprint area incorporates these variations, and provides an average interception value over the flux footprint area. Identification of light rainfall events not detected by an on-site tipping bucket rain gauge was aided by the use of a ceilometer.

Session:  Carbon - What has been learned and what further can be learned from a network of eddy covariance towers in Amazonia?.

Presentation Type:  Oral