Moisture Variation In Soils

Moisture Variation In Soils: In Relation to Surface Albedo

Studies in the past illustrated the effect of soil moisture content over the surface albedo, which are inversely related, i.e., surface albedo decreased with increasing surface soil moisture content. Among them, Idso (1975) found surface albedo to be a linear function of soil moisture content at the very thin surface layer (0–2 cm), and surface albedo corresponded slightly to the soil moisture of more than 2 cm depths. Additionally, he pointed out that the variation of bare soil surface albedo with time was symmetrical about local noon when the soil was rather wet (volumetric soil moisture content >0.20V V^-1) and rather dry (volumetric soil moisture content <0.04V V^-1). Another study measured the soil moisture of 0–2 cm at the soil surface, and found that the soil moisture content was less than 0.0075 g g-1 in dune sand with soil bulk density of 1.665 g /cm^-3 and BSCs with soil bulk density of 1.386 g cm^-3. The surface albedos exhibited random variations with increasing soil moisture content and no significant relationship was found between surface albedo and soil moisture content when the soil moisture content was less than 0.0075 g g^-1. Gu et al. (2001) assumed that the surface was in dry conditions when the surface soil moisture was less than 0.005 g g^-1 and Idso (1975) proposed a volumetric soil moisture content of less than 0.04V V^-1.We consider the surfaces as dry and soil moisture has little influence on surface albedo when soil moisture is less than 0.0075 g g^-1. Thus, by reviewing the control factors on surface albedo, it is assumed that surface albedo is predominantly controlled by solar zenith angle for the two bare and dry surfaces.