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ARS Home » Pacific West Area » Kimberly, Idaho » Northwest Irrigation and Soils Research » Research » Publications at this Location » Publication #80162
Title: TRANSLATING WIND MEASUREMENTS FROM WEATHER STATIONS TO AGRICULTURAL CROPS

Author
item ALLEN, RICHARD - UTAH STATE UNIV., LOGAN
item Wright, James

Submitted to: American Society of Civil Engineers Journal of Hydraulic Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: In arid and semi-arid climates, windspeed affects the rate of evaporation of water from land surfaces. In turn, the windspeed at some height above the surface is affected by the nature of the surface, particularly its roughness. As a result of much past research, various methods are now available to utilize windspeed measurements to estimate the evaporative loss of water, as well as other things, from various soil and crop surfaces. However, windspeeds measurements at most weather stations are over short grass or bare soil surfaces which are smooth compared to most agricultural fields. To accurately estimate crop-water-use utilizing windspeed date, it is therefore desirable to have a means of adjusting the wind-speed measurement from the weather station site to the specific agricultural field for which evaporation is being estimated. In this research study, we were able to develop and validate mathematical relationships permitting translating wind measurements from weather stations to agricultural crops. Different relationships are recommended for the various situations.

Technical Abstract: Logarithmically based functions were used to translate wind-speed measurements from weather stations to cropped fields. The translations adjusted the wind measurements for both instrument siting height and effects of vegetation height and roughness. The roughness of the original measurement site, of the vegetation for which wind data were desired and of the general region, were considered. The transfer function is necessary for wind measurements over clipped grass in order to directly predict evapotranspiration from agricultural crops using the Penman-Monteith equation. Differences in crop height and roughness between clipped grass and taller agricultural crops can reduce wind speed over the taller crops by as much as 50% in the lower internal boundary layer.