Soil Surface Roughness Effects on Radiation Reflectance and Soil Heat Flux

Abstract

Soil surface roughness provides a mechanism to alter soil reflectance and the surface energy balance. A field study was conducted to determine the effect of surface roughness on energy absorption and energy partitioning at the soil surface. A range of surface roughness conditions was created by varying the intensity of secondary tillage after moldboard plowing. Parameters measured included spectral reflectance, net radiation, soil temperature, and soil heat flux. Reflectance of solar radiation decreased with increasing surface roughness, with the greatest differences occurring among radiation wavelengths of 850 and 1350 nm. Reflectance was similar between 400 and 850 nm. Reflectance from a visibly dry surface was increased up to 25% in some wavelengths 5 d after a 47‐mm rainfall event, possibly because of decreased surface roughness. Although net radiation increased with increased surface roughness, soil heat flux at 0.01‐m was similar for all roughness conditions. This indicates that the latent and/or sensible heat flux was increased by increasing surface roughness. Theoretical considerations indicate that increasing surface roughness results in greater transport of energy from the soil surface to the atmosphere. Relationships between the change in net radiation due to surface roughness and the partitioning of net radiation among the surface energy balance components are developed and presented graphically.

Evaporation from Wavy Porous Surfaces into Turbulent Airflows

“…We distinguish between surface roughness that refers to microrelief of soil surfaces due to variations and arrangement of soil aggregates (Lehrsch et al 1987;Guzha 2004) from the general relief of a surface that represents topographical structures that are many times larger than soil aggregates. Studies of heat and mass transfer from terrestrial surfaces have shown that land relief and surface roughness may affect the surface reflectively (albedo) hence the amount of shortwave radiation absorbed at the surface (Bowers and Hanks 1965;Potter et al 1987;Raupach and Finnigan 1997;Matthias et al 2000;Cierniewski et al 2014). Surface roughness and relief have also been shown to act as momentum sinks for the atmospheric flows (Raupach 1992) affecting the aerodynamic boundary layer and turbulent interactions adjacent to the surface (Perry et al 1969;Taylor and Gent 1974;Finnigan 1988;Wieringa 1993;Raupach and Finnigan 1997).…”

“…Such effects of surface geometrical irregularities on incoming shortwave radiation and on aerodynamic boundary layer near the surface, in turn, affect exchange of energy, water, and momentum between land surfaces and the atmosphere (Jalota and Prihar 1990;Raupach et al 1992;McInnes et al 1994;Raupach and Finnigan 1997). A simple example of terrestrial surfaces with regular variations in surface relief are agricultural ridge-furrow surfaces that have been known to affect aerodynamic properties, and heat and vapor exchange dynamics at the surface (Potter et al 1987;Jalota and Prihar 1990;McInnes et al 1994). Studies have shown that short-term evaporation rates increase over such (wavy) soil surfaces (relative to a similar untilled surface) (Holmes et al 1960;Allmaras et al 1972;Jalota and Prihar 1990), whereas longer-term evaporation rates exhibited a decrease (Willis and Bond 1971;Gill et al 1977;Jalota and Prihar 1990).…”

Tillage and surface moisture effects on bare-soil albedo of a tropical loamy sand

“…For wet bare-soil, evaporation occurs at the potential rate and is a large fraction of net radiation on a daily basis (Priestley and Taylor, 1972). Higher net radiation, on a rough soil surface relative to a smooth soil surface, is partly due to a lower reflection coefficient on a rough soil surface (Coulson and Reynolds, 1971;Idso et al, 1975;Potter et al, 1987). Multiple reflections occurring between soil particles have been suggested as the mechanism to explain lower surface reflectance of a rough soil surface (Arnfield, 1975;Twomey et al, 1986).…”

Numerical analysis of the impact of charcoal production on soil hydrological behavior, runoff response and erosion susceptibility

“…Compared with pre-fire sites, Scholes & Walker (1993) and Beringer et al (2003) observed an albedo reduction of about 50 % in post-fire areas. This influences soil temperature, which in turn affects soil biophysical processes, such as seed germination, root growth, plant development and biomicrobial activity (Potter et al, 1987).…”