Chapter 8.1, Problem 3A

Sketch, label, and discuss the hydrologic cycle.

Earth's water is constantly moving between Earth's surface and atmosphere. The hydrologic cycle describes the continuous movement of water from the oceans to the atmosphere, from the atmosphere to the land, and from the land back to the sea Over most of Earth, the Quantity of precipitation that falls on the land must eventually be accounted for by the sum total of evaporation, transpiration (the release water vapor by vegetation), runoff, and infiltration

A portion of the precipitation that falls on land will soak into the ground through a process called infiltration. If the rate of rainfall exceeds the ability of the surface to absorb it, the additional water flows over the surface and becomes runoff. Runoff initially flows in broad sheets that form tiny channels called rills The rills merge to form gullies, which eventually join to create streams erosion by both groundwater and running water wears down the land and shapes Earth's surface

Figure 8.1 illustrates Earth's water balance, a quantitative view of the hydrologic cycle The figure Implies a globally uniform exchange of water between Earth's atmosphere and surface, but factors such as climate, steepness of slope, surface materials, vegetation, and degree of urbanization produce local variations

Notice in Figure 8.1 that more water evaporates from the oceans than is returned directly by precipitation. If sea level is not dropping, identify a source of water for the oceans in addition to precipitation.