Environmental Science: Toward a Sustainable Future Richard T. Wright Chapter 9 Water: Hydrologic Cycle and Human Use PPT by Clark E. Adams

Water: Hydrologic Cycle and Human Use Water: a vital resource Hydrologic cycle: natural cycle, human impacts Water: a resource to manage, a threat to control Water stewardship: public-policy challenges

Water: A Vital Resource

Hydrologic Cycle: Natural Cycle, Human Impacts Evaporation, condensation, purification Precipitation Groundwater Pools and fluxes in the cycle Human impacts on the hydrologic cycle

Polarity in H2O: The Water Molecule + - covalent bond

Condensation O H + - O H + - O H + -

Temperature Determines Whether Water Is a Gas: steam Liquid: running water Solid: ice Why does ice float?

The Water Cycle

Water Cycle Review B A D C E F H G

Condensation

Precipitation Adiabatic cooling: warm air rises, expands and cools 100% relative humidity + cooling = clouds Increasing condensation = water droplets

Global Precipitation Global precipitation distribution depends on patterns of rising and falling air currents Two main factors: global convection currents rain shadow effect

Global Air Circulation

Rain Shadow Effect

Water Balance in the Hydrologic Cycle

Pools and Fluxes in the Cycle B G I F Ground water loop Surface runoff Evapotranspiration C E D H

Human Impacts on the Water Cycle Changing the Earth’s surface Floods Climate change Atmospheric pollution Withdrawing water supplies

Groundwater Decreased infiltration Increased runoff Decreased groundwater recharge

Human Impacts on the Hydrologic Cycle

Water: A Resource to Manage, A Threat to Control Uses and sources Surface waters

Water Uses

Water Uses

Municipal Water Use and Treatment What is your community’s water source?

Surface Waters Dam impacts (see Fig. 7-15) Ecological effects of changing salinity in estuaries Increased salinity Loss of native species Invasive species increase

Consequences of Overdrawing Groundwater Falling water tables Diminishing surface waters (wetlands) Land subsidence (see Fig. 7-17) Saltwater intrusion

Aquifer Exploitation Groundwater use exceeds aquifer recharge Many remaining aquifers are heavily polluted

Saltwater Intrusion

Water Stewardship: Public-Policy Challenges Obtaining more water Groundwater Using less water Public-policy challenges

Dams Three Gorges Dam Largest in world Controls deadly floods Displaced 1.2 million people including farms, cities, homes, and factories 370-mile-long reservoir

Dams: Disrupt Integrity of River System Above the dam Flooding Sediment deposition Loss of functional floodplain Below the dam Loss of normal river flow patterns Loss of river biota

Using Less Water Irrigation Municipal uses Surge flow Drip irrigation $$$$ Municipal uses Incentives and regulations limiting water use Gray water

Desalting Seawater Reverse osmosis Distillation

Public-Policy Challenges

National Water Policy Promote water efficiency Reduce or eliminate water subsidies Charge polluters Add watershed management to pricing of water

National Water Policy United States must respond to global water crisis United States must reduce emission of greenhouse gases Need more data for informed policy decisions

End of Chapter 7