HR: 1330h
AN: H42A-1065    [PDF]
TI: Variation of Evaporation Across a Corn-Soybean Production Region in Central Iowa
AU: * Prueger, J H
EM: prueger@nstl.gov
AF: USDA-ARS National Soil Tilth Laboratory, 2150 Pammel Drive, Ames, IA 50011
AU: Hatfield, J L
EM: hatfield@nstl.gov
AF: USDA-ARS National Soil Tilth Laboratory, 2150 Pammel Drive, Ames, IA 50011
AU: Kustas, W P
EM: bkustas@hydrolab.arsusda
AF: USDA-ARS Hydrology and Remote Sensing Laboratory, Rm 104 Bldg 007 BARC-WEST, Beltsville, MD 20705-2350
AB: Evaporation from production corn-soybean surfaces is often assumed to be uniform across a regional extent such as the Upper Midwest in the U.S.; however, there are few direct measurements of the spatial and temporal variation of evaporation to support this assumption. During a soil moisture remote sensing study in the summer of 2002 (SMEX02), fourteen energy balance stations complete with net radiometers, soil heat flux plates, a three-dimensional sonic anemometer, and fast response CO2-H2O sensors (eddy covariance) were deployed across an 25-kilometer corn-soybean production watershed in central Iowa south of Ames, Iowa. Data were collected beginning in mid-May through August and summarized into half-hourly and daily intervals. Two intercomparisons of all eddy covariance systems were conducted, one prior to the SMEX02 study (May 2002) over an alfalfa field and one after the study over a grass surface in August (2002). The coefficient of variation among the eddy covariance instruments was less than 7%. Latent heat flux values among corn and soybean fields that were greater than 7% were considered to be real differences in evaporation among fields. Diurnal differences in net radiation and latent heat fluxes were evident among both corn and soybean fields and when seasonal totals were evaluated the differences persisted. Variation in latent heat flux among corn and soybeans was attributed to soil type, water availability and spatial variation of precipitation across the watershed. The results from fourteen eddy covariance stations provide a measure of the spatial variation in latent heat flux across a region that is considered to be relatively homogenous. This information will aid in evaluating regional evaporation models.
DE: 1800 HYDROLOGY
DE: 1818 Evapotranspiration
SC: Hydrology [H]
MN: 2003 Fall Meeting