From Canopies to Continents: Does Evaporation Over the Midwest Behave Like a Big Leaf?
Dr. John Norman
Tanner Chair - Department of Soil Science
Department of Atmospheric and Oceanic Science
University of Wisconsin - Madison
September 24, 1999
Abstract for Seventh Annual Kuehnast Lecture

Evaporation from natural surfaces, including transpiration, has been studied for hundreds of years because it is a major component of the water cycle, critical to wise crop management because of its effect on plant growth and irrigation scheduling, and essential for weather and climate prediction. Yet today, we cannot measure directly this critical quantity over extended areas such as large farms, counties or states. Currently, scientists can make routine measurements of evaporation on leaves, individual plants, small plots and areas up to only few hundred meters in size, so that larger-scale estimates of evaporation remain questionable. At the current time, practitioners are forced to rely on evaporation estimates from models that require inputs not obtainable on large scales. New models, which use inputs from routine satellite observations and ground-based operational weather measurements, may provide estimates of evaporation on a daily basis for spatial scales from hundreds of meters to thousands of kilometers. If successful, such products could change the way farmers manage their agricultural lands and, incidently, improve weather forecasts at the same time.

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