Detection and Use of Three Signatures of Soil-Limited Evaporation

The transition from atmosphere-limited to soil-limited evaporation is manifested in increasing surface temperature and albedo, as well as a steadying of near-surface moisture content. Each of these changes can be inferred to varying degree from ground-based and satellite-based remote sensing measurements. An evaporation model (derived for bare soil conditions) that depends on the time (td) between rainfall and this transition was tested on three interstorm periods during the first International Satellite Land Surface Climatology Project field experiment in 1987 and 1989. In general, td calculated from spatially averaged ground-based measurements of albedo, surface temperature, and surface soil moisture fell within 2 to 4 days of the td estimated from the best fit of the model to the measured evaporation rates. For the dry down spanning mid-September to mid-October 1987, albedo and daytime temperature differences estimated from geostationary operational environmental satellite (GOES) data yielded similar transition times. The effects of vegetation on model utility and on the ability to determine td from remote sensing are discussed in the context of densely and sparsely vegetated sites within the FIFE experimental area.