Chapter summary

The overall energy balance at Earth's land surface requires that the energy gained from net radiation be balanced by the fluxes of sensible and latent heat to the atmosphere and the storage of heat in soil. These surface energy fluxes are an important component of Earth's global mean energy budget and are a primary determinant of surface climate. The annual energy balance at the land surface varies geographically in relation to incoming solar radiation and soil water availability. Over land, annual evaporation is highest in the tropics and generally decreases towards the poles. Geographic patterns of evaporation are explained in the context of Budyko's analysis of the control of evaporation by net radiation and precipitation. Energy fluxes vary over the course of a day and throughout the year, also in relation to soil water availability and the diurnal and annual cycles of solar radiation. The various terms in the energy budget (net radiation, sensible heat flux, latent heat flux, and soil heat flux) are illustrated for different climate zones and for various vegetation types over the course of a year and over a day. The Penman–Monteith equation illustrates relationships among net radiation, latent heat flux, sensible heat flux, and surface temperature. Soil experiments that alter surface albedo, surface resistance to evaporation, and thermal conductivity illustrate the importance of these surface properties in regulating surface temperature and energy fluxes.