Influence of the atmosphere
Surface water hydrologie processes represent the dynamic expression of the flux of moisture to, across, and from the land surface. The primary control on this moisture flux is climate, which in turn, is controlled by the general circulation of the atmosphere. Thus, in order to understand the nature and characteristics of surface water hydrology, it is first necessary to understand the atmospheric context within which surface water processes occur. In this chapter we present this context in a conceptually broad, but topically systematic way. The chapter content includes empirical information developed over many decades of observation. .We develop a more contemporary perspective, however, by characterizing these observations in a framework that draws on the current thinking associated with global change, especially with respect to climate variability and change.
The chapter begins with an overview of the concepts and elements associated with the fluxes of energy and moisture to, across, through, and from the land surface. In particular, emphasis is placed on the characteristics of the surface energy balance, especially the fluxes of latent and sensible heat. Additionally, the primary terrestrial components of the hydrologie cycle— évapotranspiration, runoff, and soil moisture—are discussed.
From this description of the atmospheric “engine” we proceed to a characterization of the climate and hydrologie effects that result from the operation of the atmospheric “engine.” This includes the general atmospheric circulation (i.e., the weather delivery system), the climatology of North American extratropical and tropical storms, patterns and trends in North American droughts, regional hydroclimatic conditions, and an overview of the hydrologie cycle over North America.