Quantifying the Roles of Changing Albedo, Emissivity, and Energy Partitioning in the Impact of Irrigation on Atmospheric Heat Content

摘要

Introduction of irrigated agriculture changes the partitioning of the surface energy flux between sensible and latent heat (H vs LE) and alters the albedo alpha and emissivity epsilon. In the absence of changes in the radiation components of the surface energy balance, the change in the Bowen ratio due to irrigation typically suppresses the local air temperature T but increases the total near-surface atmospheric heat content (as measured using equivalent potential temperature theta(e)). While the effect of irrigation on surface energy partitioning due to enhanced surface and subsurface water availability has long been acknowledged, the roles of associated changes in epsilon and alpha have received less attention, and the scales and magnitudes of these effects remain uncertain. A new methodology designed for application to in situ and remote sensing data is presented and used to demonstrate that the net impact of irrigation on T and theta(e) is strongly dependent on the regional climate, land cover in surrounding areas, and the amount of irrigation in the upwind fetch. The results suggest that the impact of the radiative forcing terms on net available energy is not negligible and may amplify or offset the impact from changed energy partitioning on T and theta(e) depending on the specific regional climate and land cover.