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United States Department of Agriculture

Agricultural Research Service

Title: Variability in Soil Heat Flux from a Mesquite Dune Site

Authors
item Kustas, William
item Prueger, John
item Hatfield, Jerry
item Ramalingam, Kalia - UTAH ST UNIV, LOGAN, UT
item Hipps, Lawrence - UTAH ST UNIV, LOGAN, UT

Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 11, 2000
Publication Date: August 15, 2000

Interpretive Summary: For many natural and agricultural landscapes, vegetation partially covers the ground surface resulting in significant variations in soil heat flux between interspace areas and underneath vegetation. This is exacerbated in arid and semi-arid regions where vegetation cover is low and clumped with large areas of exposed soil. Surface heterogeneity presents significant challenges to the use of standard micrometeorological measurement techniques for estimating evapotranspiration (ET). There is clearly an uncertainty as to the number of soil heat flux sensors required to obtain a representative soil heat flux for most heterogeneous surfaces. Obviously, there are practical limitations to the number of sensors one can use to obtain a representative value within several meters of the ET measurement tower. This limitation is more pronounced when trying to obtain representative values commensurate with the area influencing the ET measurements which is typically several hundred meters upwind. The objective of this study was to use an array of 20 soil heat flux plates and soil temperature sensors to characterize the spatial and temporal variability in soil heat flux as affected by vegetation and micro-topographic effects in mesquite dunes. Results indicate positioning sensors in complex terrain must be considered carefully to provide reliable values for ET measurement systems.

Technical Abstract: For many natural and agricultural landscapes, vegetation partially covers the ground surface resulting in significant variations in soil heat flux between interspace areas and underneath vegetation. This is exacerbated in arid and semi-arid regions where vegetation cover is low and clumped with large areas of exposed soil. The objective of this study was to use an array of 20 soil heat flux plates and soil temperature sensors to characterize the spatial and temporal variability in soil heat flux as affected by vegetation and micro-topographic effects in mesquite dunes of the Jornada Experimental Range in southern New Mexico. Maximum differences in soil heat flux among sensors were nearly 300 and 250 Watts per meter squared among individual sensors under similar cover conditions. The "area-average" soil heat flux from the array was compared to a three-sensor network from a nearby micrometeorological station. Comparisons between the array-average soil heat flux and the three-sensor network indicate that differences reach a maximum on the order of 50 to 80 Watts per meter squared in the early morning and mid-afternoon periods which are likely due to shadowing effects from the vegetation and micro-topography. Larger differences are likely in areas where the fractional cover is still sparse but higher than the 25 percent cover estimated at this site. Positioning sensors in complex terrain must be considered carefully to provide reliable values of energy exchange parameters.

Last Modified: 12/19/2014
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