Water: Hydrologic Cycle and Human Impact

1. CHAPTER 10 Water: Hydrologic Cycle and Human Use

2. Introduction to water The former Soviet Union was responsible for the death of the Aral Sea in Central Asia It was once the fourth largest lake on Earth Two rivers were tapped for irrigation for cotton Eliminating inflow of water into the Aral The Aral Sea began to shrink The commercial fishery collapsed 60,000 fishermen lost their jobs

3. The shrinking Aral Sea The lake lost 90% of its volume The water level dropped by 53 feet The surface area shrunk greatly The sea separated into the southern Big Aral and the northern Small Aral The Big Aral is too salty for fish Windblown salt and dust cause asthma and cancer The climate has changed Unique animals have gone extinct

4. Regime change The future of the Aral Sea is in the hands of Uzbekistan, Kazakhstan, Turkmenistan, Tajikistan, and Kyrgyzstan Struggling countries that use water for irrigation There is little hope of restoring the Aral Sea A restoration project is helping the Small Aral Only brine shrimp survive in the Big Aral The Rio Grande and Colorado rivers are drying up The Dead Sea is dying because of water diversion Domestic, industrial, and agricultural use compete for limited water

5. Water: a vital resource Water is fundamental to life Earth is flooded with water Covering 75% of the Earth’s surface 97.5% of all water is salt water (oceans, seas) Fresh water: contains < 0.1% (1,000 ppm) salt 67% of fresh water is bound up in ice caps and glaciers Only 0.77% of all water is in lakes, wetlands, rivers, groundwater, biota, soil, and the atmosphere Evaporation and precipitation cycle water through the solar-powered hydrologic cycle

6. Earth’s water

7. Freshwater is a renewable resource Streams, rivers, ponds, lakes, swamps, estuaries, groundwater, bays, oceans, and atmosphere contain water They represent ecosystem capital (goods and services) Water is used for drinking, industries, irrigation, energy, transportation, recreation, waste processing, habitats Water modifies the climate Humans have constructed huge infrastructures to control water Dams, canals, reservoirs, aqueducts, sewer systems Treatment plants, water towers, pipelines, irrigation Desalinization plants

8. Water in developed and developing nations Developed countries benefit from controlling water Controlling diseases, building cities in deserts, irrigation, electricity Water in developing countries is costly or inaccessible They lack access to safe drinking water and sanitation People die from waterborne diseases Because of infrastructure to control water Seas and rivers are being lost Millions have been displaced to make room for reservoirs Tensions increase for access to water

9. Differences in availability

10. Future challenges Increasing population will challenge water management infrastructure Increasing agricultural output Cities and industries compete with agriculture Climate change will affect the hydrologic cycle Rainfall variability will cause floods and droughts There are two ways to consider water issues Quantity Quality

11. Hydrologic cycle Hydrologic (water) cycle: the cycling of water through the Earth Evaporation and transpiration: water rises to the atmosphere Condensation and precipitation: water returns to the land and oceans Green water: water in vapor form Blue water: water in liquid form

12. The hydrologic cycle

13. The hydrologic cycle Animation: Hydrologic Cycle

14. Water cycle scramble Animation: Hydrologic Cycle Scramble

15. Evaporation Hydrogen bonding holds water molecules (H2O) together Below freezing (32°F, 0°C): low kinetic energy allows hydrogen bonding to hold molecules in place as ice Above freezing but below boiling: the kinetic energy allows hydrogen bonds to break and re-form as liquid Evaporation: as water molecules absorb energy from the Sun, kinetic energy allows molecules to enter the atmosphere Water vapor: water molecules in the gaseous state

16. Water vapor is a greenhouse gas Water vapor contributes two-thirds of the warming of all greenhouse gases Humidity: amount of water vapor in the air Relative humidity: the amount of water vapor as a percent of what the air can hold at a particular temperature The amount of water vapor the air can hold varies with the temperature Cooling causes water vapor to condense to liquid water

17. Condensation

18. Condensation Condensation is the opposite of evaporation Water molecules rejoin by hydrogen bonding, forming liquid water Fog and clouds: droplets forming in the atmosphere Dew: droplets forming on vegetation Aerosols: microscopic liquid or solid particles Help condensation occur Originate naturally from volcanoes, dust, soil, salt Human sources: sulfates, carbon, dust

19. Purification Evaporation and condensation purify water naturally Evaporation removes only water molecules, not salts and other solids Atmospheric water turns over every 10 days Water is constantly purified Evaporation and condensation are the source of all fresh water Water eventually reaches the oceans, inland seas, lakes Evaporation and transpiration return water to the atmosphere

20. Precipitation Warm, less dense air rises Adiabatic cooling: warm air gradually cools as it rises and expands Adiabatic warming: occurs as cold air descends and is compressed by higher air pressure Earth’s precipitation ranges from near zero to 2.5 meters (100 in.) per year The distribution depends on rising and falling air currents

21. Air currents affect precipitation Rising air cools and condenses Precipitation results Descending air warms, causing evaporation Dryness results A cold front causes warm, moist air in the area to rise The cold air of the advancing front is denser The rising warm air cools and condenses and precipitation occurs Global convection currents and rain shadows cause rising and falling air currents and affect precipitation

22. Global precipitation

23. Convection currents Convection currents occur because the Sun heats the Earth most intensely over and near the equator Heated air expands, rises, and cools Condensation and precipitation occur The equator’s constant heat causes this process to repeat Supporting tropical rain forests The now dry air “spills over” north and south of the equator Descending over subtropical areas and creating deserts Hadley cell: the system composed of rising and falling air Trade winds: Earth’s rotation deflects winds east and west

24. Hadley cells Animation: Hadley Cells

25. Global air circulation

26. Rain shadow Moisture-laden trade winds encounter mountain ranges The deflected air rises and cools and precipitation occurs on the windward side of the mountains Air crossing the mountains warms and picks up moisture Deserts occur on the leeward sides of mountains Rain shadow: the dry region downwind of a mountain range Causes the severest deserts in the world For example, Death Valley, east of the Sierra Nevada mountains in California

27. Rain shadow

28. Groundwater Precipitation can either soak into the ground (infiltration) or run off the surface Infiltration-runoff ratio: the amount of water that soaks into the ground compared with the amount that runs off Runoff flows into streams and rivers, eventually reaching oceans or inland seas Watershed: all the land area contributing to a stream or river Surface waters: ponds, lakes, streams, rivers, etc. on the Earth’s surface

29. Infiltrating water has two alternatives Capillary water: held in the soil, according to the soil’s capacity Returns to the atmosphere by evaporation or transpiration (green water flow) Evapotranspiration: the combination of evaporation and transpiration Gravitational water: is not held in the soil Percolation (blue water flow): trickling of water through pores or cracks in the soil

30. Groundwater and the water table Groundwater: water accumulated in the earth It lies on top of an impervious layer of rock or clay Water table: the upper surface of groundwater Gravitational water becomes groundwater when it reaches the water table Wells dug below the water table allow groundwater to seep into the well The groundwater fills the well to the level of the water table

31. Recharge Groundwater seeps laterally as it seeks its lowest level Aquifers: layers of porous material through which groundwater moves It is hard to determine the location of aquifers Layers of porous rock are found between layers of impervious rock The entire formation may be fractured and folded Recharge area: the area where water enters an aquifer May be miles away from where water leaves the aquifer Aquifers hold 99% of all liquid water

32. Underground purification As water percolates through the soil, debris and bacteria are filtered out Water may dissolve or leach out minerals Some minerals can be dangerous (arsenic, sulfide, etc.) Drawn by gravity, groundwater moves through aquifers until it finds an opening to the surface Seep: water flows out in a wide area Spring: water flows from a small opening Seeps and springs feed streams, lakes, and rivers

33. Loops, pools, and fluxes The hydrologic cycle has four physical processes: evaporation, condensation, precipitation, and gravitational flow It also has three major loops Evapotranspiration loop: green water that evaporates and returns by precipitation The main source for ecosystems and natural agriculture Held as capillary water It returns to the atmosphere by evapotranspiration

34. Other loops of the hydrologic cycle Surface runoff loop: blue water across the ground’s surface Becomes part of the surface water system Groundwater loop: blue water that infiltrates, percolates, and joins groundwater Moves through aquifers and exits through seeps, springs, and wells to rejoin surface water These two loops are the focus for human water resource management The hydrologic cycles “fluxes”: the exchange of water among land, atmosphere, and oceans

35. Yearly water balance in the hydrologic cycle

36. Human impacts on the hydrologic cycle Many environmental problems stem from direct or indirect impacts on the water cycle Four categories of impacts: Changes to Earth’s surface Changes to Earth’s climate Atmospheric pollution Withdrawals for human use

37. Changes to the surface of the Earth In natural systems, vegetation intercepts precipitation Water infiltrates into porous topsoil, filtering out debris Evapotranspiration sustains ecosystems and recycles water Recharged groundwater reservoirs release water through springs and seeps into streams and rivers In cleared forests and overgrazed land, plants do not intercept rainfall Water shifts from infiltration and recharge into runoff

38. Cleared land affects the hydrologic cycle Removing vegetation causes a sudden influx of water into rivers and streams Causing floods, pollutants from erosion, and less evapotranspiration and groundwater recharge Resulting in dry, barren, lifeless streambeds Wetlands also store and release water Destruction leads to flooding and polluted waterways Wetlands dry up during droughts In 2008, Iowa had massive flooding due to filling wetlands and converting tallgrass prairies to plowed fields

39. Climate change There is unmistakable evidence that Earth is warming Increasing greenhouse gases are changing the water cycle Evaporation increases with a warmer climate A wetter atmosphere means more and heavier precipitation and floods More hurricanes and droughts Water-stressed areas (e.g., East Africa) will get less water Global warming may be speeding up the water cycle Affecting precipitation, evapotranspiration, groundwater recharge, runoff, snowmelt, etc.

40. Atmospheric pollution Aerosol particles form nuclei, enabling water to condense into droplets More clouds form Anthropogenic particles are increasing From sulfates, carbon (soot), dust Form a brownish haze associated with industrial areas, tropical burning, and dust storms Solar radiation is reduced Aerosols have a cooling effect

41. Aerosols affect the water cycle They promote smaller droplets They suppress rainfall, even though clouds form Aerosols suppress atmospheric cleansing They cause aerosols to remain in the air longer, further increasing drier conditions Dust, smoke, and aerosols increase Aerosols work differently from greenhouse gases Aerosols have more local (vs. global) impacts They do not accumulate—they have a lifetime of days

42. Water: management and control Humans use 27% of all accessible freshwater runoff Global withdrawal will increase 10% each decade Americans use less water than in 1980 Nonconsumptive uses of water: water may be contaminated, but is still available to humans Used in homes, industries, and electric power production Consumptive uses of water: the applied water does not return to the water resource It is gone from human control Water for irrigation

43. U.S. trends in population and freshwater withdrawals

44. Uses of water Worldwide, the largest use is for irrigation Then industry and direct human use Use varies by region, depending on: Natural precipitation Degree of development Most increases in withdrawal are due to increases in agriculture Irrigation accounts for 65% of freshwater consumption in the U.S.

45. Regional usage of water

46. Sources of water 37% of domestic water comes from groundwater sources 63% comes from surface water (rivers, lakes, reservoirs) Rural people in developing nations get water where they can Wells, rivers, lakes, rainwater Women often have to walk long distances to get water Water in developing nations is often polluted with waste 1.1 billion people use polluted water 1.6 million (mostly children) die each year Millennium Development Goal 7: increase access to safe drinking water

47. Water in the developing world

48. Technologies in developed nations Industrialized countries collect, treat, and distribute water Larger municipalities rely mostly on surface water Dams create reservoirs to generate power and for recreation, irrigation, flood control Water is piped to a treatment plant It is then distributed to homes, schools, industries After use, it is collected by the sewage system and treated It is then released downstream into the same river Water is reused many times on major rivers (e.g., Mississippi)

49. Municipal water use and treatment

50. Technologies in other areas In developing nations, wastewater is often discharged with little or no treatment Cities downstream have much higher pollution loads Ecosystems can be severely affected by pollution Smaller public drinking-water systems depend on groundwater Water is purified by percolation Surface and groundwater represent a sustainable or renewable (self-replenishing) resource But they can be overdrawn