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.

Where’s the Water? 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? (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 Cycle Oceans Reservoirs of liquid water Precipitation Water falling on earth in liquid (rain) or solid (snow) form Evaporation and Transpiration The drawing of water into the atmosphere from water bodies (evaporation) or plants (transpiration) Surface Water Ponds, lakes, and streams Groundwater Subsurface 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)

Groundwater Infiltration Zone of aeration Zone of Saturation Precipitation (rainfall and snowfall) seep into the soil Zone of aeration Pore spaces between soil grains contain air and water Soil moisture in this zone is known as Capillary water Zone of Saturation Pore spaces between soil grains are filled with water Soil moisture here is Groundwater

Groundwater Capillary water Groundwater Impervious Surface

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)

Groundwater Aquifer Water table Aquifer recharge zones Underground body of water Water table the boundary between the unsaturated and saturated zones Aquifer recharge zones Areas 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)