Water Resources

About the Hydrologic Cycle• Hydrology is the study of movements

and characteristics of water.

• The hydrologic cycle has a profound

effect upon climate prediction.

• Water is vital so we must understand

where to find water and how water

supplies cycle through the Earth.

FIGURE 11.2 The distribution of water on Earth. [Data from J. P. Peixoto and M. Ali Kettani, “The Control of the Water Cycle.” Scientific American (April 1973): 46; E. K. Berner and R. A. Berner, Global Environment. Upper Saddle River, N.J.: Prentice Hall, 1996, pp. 2–4.]

Where ’s the Water?

Where’s the Water?

(C & R p. 228)

Renewal time: the time required for the complete replacement of the water in a specific part of the cycle.

Flows and Reservoirs• Precipitation: water vapor condenses into tiny

drops that form clouds, eventually fall as rain or snow

• Infiltration: when precipitation soaks into the ground through particles of soil or cracks

• Runoff: precipitation that doesn’t infiltrate moves over the land surface, eventually collecting in streams and rivers

• Evaporation: liquid water transforming into gaseous water (water vapor)

• Sublimation: solid water (ice) transforming directly into gaseous water (without becoming liquid)

Key Parts of The Water CycleOceans

Reservoirs of liquid waterPrecipitation

Water falling on earth in liquid (rain) or solid (snow) form

Evaporation and TranspirationThe drawing of water into the atmosphere from

water bodies (evaporation) or plants (transpiration)

Surface WaterPonds, lakes, and streams

GroundwaterSubsurface water storage

The Water Cycle

Figure 10.1 The water cycle. This illustration shows the flow of water through the water cycle.(C & R p. 227)

The Hydrologic Cycle

Numbers indicate thousands of km3/year

Precipitation

Figure 10.3 Average annual precipitation in the United States.(C & R p. 229)

GroundwaterInfiltration

Precipitation (rainfall and snowfall) seep into the soil

Zone of aerationPore spaces between soil grains contain air and

waterSoil moisture in this zone is known as

Capillary waterZone of Saturation

Pore spaces between soil grains are filled with water

Soil moisture here is Groundwater

Impervious Surface

Groundwater

Groundwater

Capillary water

Groundwater

Figure 10.5 Fate of water that has fallen on the ground as precipitation. This drawing also shows how an aquifer is formed. (C & R p. 231)

GroundwaterAquifer

Underground body of water

Water tablethe boundary between

the unsaturated and saturated zones

Aquifer recharge zonesAreas where

precipitation can infiltrate the soil and add water to the aquifers

Figure 10.6 An aquifer serves as a source of well water. Continued withdrawal of water would eventually deplete the supply if the rate of withdrawal exceeded the rate of recharge.(C & R p. 231)