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United States Department of Agriculture

Agricultural Research Service

Title: Advection Influences on Evapotranspiration of Alfalfa in a Semiarid Environment

Authors
item Tolk, Judy
item Evett, Steven
item Howell, Terry

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 24, 2006
Publication Date: December 1, 2006
Citation: Tolk, J.A., Evett, S.R., Howell, T.A. 2006. Advection influences on evapotranspiration of alfalfa in a semiarid environment. Agronomy Journal. 98:1646-1654.

Interpretive Summary: Advection, which is the transport of hot, dry air into a cool irrigated crop by wind, can greatly increase the water use by the crop in a semiarid climate. We evaluated 13 days of the water loss from an alfalfa crop to see how much was due to advection. We found that about 30% of the evaporated water from the crop was due to energy from the sun, and the rest was due to hotter, drier air from the surrounding landscape passing over the crop. This shows that advection plays a major role in the water balance of this region.

Technical Abstract: Advective enhancement of crop evapotranspiration (ET) occurs when drier, hotter air is transported into the crop by wind and can be an important factor in the water balance of irrigated crops in a semiarid climate. Thirteen days of moderate to extremely high ET rates of irrigated alfalfa (Medicago sativa L.) were evaluated using energy balance and atmospheric coupling models to examine the magnitude of ET enhancement due to advection. Alfalfa ET was measured using precise, monolithic weighing lysimeters. The average ET of the selected days was 11.7 mm, with ET exceeding 15 mm on three days, with average vapor pressure deficit (VPD) of 2.1 kPa and wind speed of 4.4 ms -1. Evapotranspiration due to available energy (net radiation + soil flux) was fairly stable at an average of 3.4 mm d-1 while advect4ed atmospheric deficits and sensible heat flux added as much as 15 mm d-1 to ET, with sensible heat (H) gain providing an average of 38% of the energy used in ET. Overnight ET losses due continued H flux gains and VPD resulted in ET losses as large as 3.2 mm. Widespread precipitation tended to modify the effects of regional advection on the irrigated alfalfa ET, but the advective enhancement of ET was restored within several hours. Advective enhancement of ET plays a significant role in the water balance of the semiarid region of the southern High Plains.

Last Modified: 7/22/2014
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