Water covers 70% of the earth's surface the oceans contain 97.5% of the earth's water, land 2.4%, and the atmosphere holds less than .001%. The annual precipitation for the earth is more than 30 times the atmosphere's total capacity to hold water. This fact indicates the rapid recycling of water that occurs between the earth's surface and the atmosphere. Water is transferred from the surface to the atmosphere through evaporation, the process by which water changes from a liquid to a gas.

Approximately 80% of all evaporation is from the oceans, with the remaining 20% coming from inland water and vegetation. Winds transport the evaporated water around the globe, influencing the humidity of the air throughout the world. Most evaporated water exists as a g

Groundwater is all the water that has penetrated the earth's surface and is found in one of two soil layers. The one nearest the surface is the "zone of aeration", where gaps between soil are filled with both air and water. Below this layer is the "zone of saturation", where the gaps are filled with water. The water table is the boundary between these two layers. As the amount of groundwater water increases or decreases, the water table rises or falls accordingly. When the entire area below the ground is saturated, flooding occurs because the rest of the precipitation is forced to remain on the surface.

In meteorology, convection refers primarily to atmospheric motions in the vertical direction. As the earth is heated by the sun, different surfaces absorb different amounts of energy and convection may occur where the surface heats up very rapidly. As the surface warms, it heats the overlying air, which gradually becomes less dense than the surrounding air and begins to rise. The bubble of relatively warm air that rises upward from the surface is called a "thermal".

Water that infiltrates the soil flows downward until it encounters impermeable rock, and then travels laterally. The locations where water moves laterally are called "aquifers". Groundwater returns to the surface through these aquifers, which empty into lakes, rivers, and the oceans. It is also possible for groundwater to flow upward in artesian wells. The flow of groundwater is much slower than runoff, with speeds usually measured in centimeters per day, meters per year, or even centimeters per year.

The amount of water that can be held in the soil is called "porosity". The rate at which water flows through the soil is its "permeability". Different surfaces hold different amounts of water and absorb water at different rates. Surface permeability is very important for hydrologists to monitor because as a surface becomes less permeable, an increasing amount of water remains on the surface, creatin

Some topics in this essay:
Instability CISK, Midwestern United, Cycle Water, water vapor, air rises, rising motion, hydrologic cycle, condensation occurs, condenses produce, earth's water, water atmosphere, earth's surface, cold front, warm air rises, moisture condenses produce, air rises cools, condenses produce clouds, water vapor condenses,