1. Precipitation in North America Figure 9.5

2. Potential Evapotranspiration Figure 9.6

3. Figure 9.10 U.S. Drought Monitor Water Year: October ~September A commonly used drought index: P/PET

4. Sample Water Budget Figure 9.11

5. Sample Water Budgets Figure 9.12

6. Annual River Runoff Figure 9.13

7. Water resources that lie below the soil moisture root zone. It is the largest potential freshwater resources in the hydrologic cycle. Groundwater is not an independent sources of water, but recharged by surplus water at surface. Some groundwater accumulation takes millions of years, thus not easily replenished if overdrawn. Groundwater Resources

8. Surface Water Profile Root zone Capillary fringe layer Ground water Zone of Aeration: Part of the pore space is filled with air. Water table Zone of saturation All pore space is filled with water Capillary rise: liquid water rises through fine linear space

9. Groundwater Characteristics Figure 9.17 Aquifer: a rock layer that is permeable to groundwater flow adequate for wells and springs. Confined: bounded above and below with impermeable layers, thus high water pressure and easy to extract. Unconfined: permeable layer on top and impermeable layers below, thus easily recharged from above, but need pump to draw water.

10. Forming a Cone of Depression

11. Groundwater Characteristics Figure 9.17

12. Groundwater and Streamflow Figure 9.19 Humid climate (e.g. Mississippi River) Dry climate (e.g. Colorado River)

13. Figures FS 9.2.1a, 9.2.3 Two Problems 1.Overdrawn. Due to demand for agricultural, industrial and urban use, groundwater table is decreasing. 2.Pollution: groundwater is recharged with surface water. Pollution of ground water will lead to pollution of groundwater, including, septic tank outflows, land fills, pestcides, herbcides, fertilizers, industrial waste injections etc. point sources non-point sources

14. Water Supply in the United States Instream, Nonconsumptive, and Consumptive Uses Desalination Future Considerations Our Water Supply

16. U.S. Water Budget Figure 9.20 Navigation, hydroeclectric power, fishing, recreation etc. Water quality changes: Toxic pollutants To much nitrogen Higher temperature

17. Water Withdrawal by Sector Figure 9.21