Natural Hazards and Disasters Chapter 10 (part A) Climate Change and Weather Related to Hazards

1. Natural Hazards and Disasters Chapter 10 (part A) Climate Change and Weather Related to Hazards

2. System Feedback • Feedback loops • Positive • Negative • Positive feedback loops encourage a dynamic state • Processes in motion are continuous, but move away from the original condition • Negative feedback loops encourage a steady state • Processes are again continuous, but produce the same state(s) over and over

3. System Equilibrium • The maintenance of structure and character over time • Three types • Steady-state • Dynamic • Metastable • Also called punctuated

4. System Feedback

5. System Feedback

6. System Feedback • Which is • Positive? • Negative?

7. Rapid Melting in the Arctic • August, 2005: giant mass of ice cracked off Ellesmere Island ice shelf near North Pole • Mass formed more than 3000 years ago • Largest loss in 30 years • Ice shelves of northern Canada are now 90% smaller than when first surveyed in 1906 • From 1979 to 2005, extent of Arctic sea ice declined about 8% per decade • Exposed water absorbs nine times more solar radiation than ice  causes more melting

8. Basic Elements of Climate and Weather • Weather: conditions of atmosphere at particular place and time • Temperature, air pressure, humidity, precipitation, air motion • Climate: weather of area averaged over long time • “Climate is what you expect, weather is what you get” • Significant effects on hazards, involving coastal erosion, hurricanes, thunderstorms, tornadoes, wildfires

9. Hydrologic Cycle Water in oceans covers more than 70% of Earth’s surface Less than 3% of water on Earth is fresh Derived from evaporation of ocean water Some water precipitates over continents as rain or snow Most rain that is not taken up by plants soaks in to become groundwater Groundwater seeps back to surface into lakes and rivers and ultimately flows back to sea All part of hydrologic cycle

10. Hydrologic Cycle • Amount of water vapor that can be dissolved in air depends on air temperature • Cold air can dissolve little water vapor • Warm air can dissolve a lot of water vapor • When air dissolves maximum water vapor that it can hold: • It is saturated • Its relative humidity is 100% • Temperature at which air’s relative humidity would be 100% is dew point • If water cools below dew point, water condenses into droplets • If enough droplets form, coalesce into larger droplets and precipitate as rain or snow

11. Hydrologic Cycle • Rain or snow falling onto continents can: • Fall on vegetation, where some water evaporates back into atmosphere • Reach ground • Run off into streams or lakes • Be taken up by plant roots into leaves, be transpired back into atmosphere • Soak into ground to become groundwater • Groundwater slowly migrates in direction that water table slopes (downhill) into streams, lakes and wetlands • Streams, lakes and wetlands eventually drain back into ocean

13. Adiabatic Cooling and Condensation • Adiabatic cooling occurs when rising air expands without change in heat content • Rate of cooling as air mass rises is adiabatic lapse rate • Expansion of air mass distributes heat over larger volume, so air becomes colder • During condensation (water vapor into liquid water), air releases same amount of heat as originally required to convert liquid water into water vapor • Heat of condensation reduces adiabatic lapse rate for wet air mass to 5°C per 1000 m of rise, from 10°C per 1000 m of rise for dry air mass • Very wet air cools at half rate of dry air as it rises

14. Adiabatic Cooling and Condensation

15. Adiabatic Cooling and Condensation Air moving over continent may be forced to rise over mountain range, so expands and cools in orographic effect Cooler air can hold less moisture, so precipitation occurs as air mass rises Air moving down other side of mountain range is then warmer and drier Rain shadow effect creates deserts on downwind side of mountain ranges

16. Atmospheric Pressure and Weather • Air pressure is related to weight of column of air from ground to top of atmosphere • Heating an air mass causes it to expand (causes its density to decrease), so air mass rises and has lower pressure • Air near ground surface is pulled in toward low-pressure center to replace rising air • Opposite occurs in high-pressure systems • Air flows from high-pressure to low-pressure areas, causing winds • Greater pressure difference  stronger winds

17. Atmospheric Pressure and Weather

18. Coriolis Effect • Because Earth rotates from west to east, large masses of air and water on its surface tend to lag behind a bit • Point on equator travels 40,000 km in a day’s rotation • Point at pole travels no distance in rotation • Oceans and air masses near equator move from east to west because they are fluid and not pulled at same speed as solid Earth’s rotation • In northern hemisphere: • Water or air moving south will veer off to west • Water or air moving north will veer off to east • In southern hemisphere, opposite is true • Forced curvature of path due to Earth’s rotation is Coriolis effect

19. Coriolis Effect

20. Coriolis Effect Rising and falling air currents also rotate because of converging or diverging winds Air converges toward low-pressure system and is shifted to right of straight in northern hemisphere  counterclockwise rotation Air diverges away from high-pressure system and is shifted to right of straight in northern hemisphere  clockwise rotation Right-hand rule in northern hemisphere Air that rises faster will also rotate faster

21. Global Air Circulation • At approximately 30°N and 30°S, air sinks to form subtropical high-pressure zones, returns to equator • Sinking air warms adiabatically and becomes dry, forms deserts at 30°N and 30°S • Atmospheric heating is dominant at equator • Cooling is dominant at poles • Less-dense warm air rises at equator, so surface air moves toward low-pressure equatorial regions • Rising air above equator spreads to north and south • The Hadley Cell • At approximately 30°N and 30°S, air sinks to form subtropical high-pressure zones, returns to equator • Sinking air warms adiabatically and becomes dry, forms deserts at 30°N and 30°S

22. Global Air Circulation • Combination of global air movement with Coriolis effect forms: • Southwest-moving trade winds between equator and 30° latitude • Northeast-moving westerly winds between 30° and 60°

23. Global Air Circulation • Local wind patterns form around mountain ranges • Strong western winds cool and lose moisture as they rise over Rocky Mountains • Western winds form strong downslope winds that warm adiabatically across Plains states  Chinook winds • Same effect in southern California produces Santa Ana winds

24. Weather Fronts • Severe weather is often associated with weather fronts, boundaries between cold and warm air masses • Cold front: • Cold air mass overtakes warm air mass, causing rapid lift and displacement of warm air • Rapidly lifted warm air causes instability, condensation, precipitation • Warm front: • Warm air mass overtakes cold air mass, rising over it • Forms widespread clouds and storms

25. Weather Fronts

26. Jet Streams Jet stream: narrow, 3-4 km thick ribbon of high-velocity winds blowing from west to east at altitudes near 12 km Over North America, jet stream marks boundary between warm, moist subtropical air and cold, dry air to north Storms often form along fronts near jet stream

27. Climatic Cycles The Milankovitch Cycle and Precession Earth’s atmosphere is subject to cyclic changes Many cyclic changes have impact on weather-related hazards

28. Days to Seasons • Heat building during daytime hours can cause afternoon thunderstorms and tornadoes: daily cycle • Many climate-controlled hazards are part of seasonal cycles • Hurricanes occur from summer through fall • Tornadoes occur from spring through summer • Earth is NOT closer to sun in summer • Two hemispheres of Earth experience summer at different times

29. Days to Seasons • Earth’s axis of rotation is tilted 23.5° to plane of Earth’s orbit around sun • Northern hemisphere receives maximum solar radiation when sun points directly at 23.5°N (at summer solstice) • Warmest temperatures lag behind by about a month – takes time to heat up land and water • Other observed cyclic changes in northern hemisphere climate may be explained by • Changes in ocean currents • Changes in solar radiation caused by changes in Earth’s orbit • Plate tectonic movements • Changes in atmospheric composition

30. Days to Seasons

31. El Niño • Oceanic circulation in equatorial Pacific usually is pushed westward by trade winds • Warm surface water off Peru is blown westward and replaced by upwelling of cold, deep, nutrient-rich water (productive fisheries) • Every six years (on average), Pacific Ocean circulation reverses in pattern called El Niño • Subtropical trade winds weaken • Warm surface water remains in east Pacific • Incessant rain to west coasts of North and South America • Fisheries suffer (no cold, nutrient-rich upwelling water) • Opposite extreme in weather patterns is La Niña

32. El Niño

33. North Atlantic Oscillation • Recurring atmospheric pressure pattern in northern Atlantic Ocean • No correlation to El Niño • Variations in winter atmospheric pressure over northern Atlantic Ocean • Positive NAO: • High pressure centered over eastern Atlantic Ocean • Low pressure centered over northern Atlantic Ocean • Strong prevailing westerly winds • Warm weather across Atlantic Ocean and northern Europe • Negative NAO: • Both pressure systems shift to southwest • Weaker westerly and trade winds

34. NAO

35. Atlantic Multidecadal Oscillation • Longer-term changes in sea surface temperature of northern Atlantic Ocean • From slightly cooler to slightly warmer (0.8°C), over about 70 years • Warmer periods  wetter summers in southeastern U.S., more or stronger hurricanes • Changes correlate to: • Strength of Atlantic Ocean’s large-scale circulation • Drought in American Midwest • Abnormally wet weather in southern Florida • Rainfall in Sahel of Africa

36. Atlantic Multidecadal Oscillation

39. Long-Term Climatic Cycles 26,000-year cycle of direction of Earth’s axis (precession) results in different amounts of solar radiation reaching parts of Earth 41,000-year cycle ranges tilt of Earth’s axis from 22° to 24.5° (present tilt is 23.5°)

40. Long-Term Climatic Cycles • Longer cycles include Pleistocene ice ages for last 2 million years • 20 ice ages recorded in ice cores • Last about 100,000 years • Irregular advances with lesser retreats to maximum ice cover, followed by rapid retreat to minimum ice cover • Milankovitch in 1920s calculated changes in Earth’s orbit from nearly circular to elliptical over 100,000 years  correlates to Pleistocene ice ages

41. Long-Term Climatic Cycles • Past global temperatures are estimated from oxygen-isotope ratios (18O:16O) preserved in sedimentary material, glacial ice or marine organisms’ shells • Cooler times: • More water stored on continents as ice and snow • Evaporation preferentially takes lighter 16O  oceans become enriched in heavier 18O • Long-term variations in climate • Warm usually coincides with wet • Major cycles can last tens of millions of years or longer

42. Hazards Related to Weather and Climate • Many hazards are related to weather • Floods • Hurricanes and nor’easters • Thunderstorms and tornadoes • Droughts • Heat waves • Snow and ice • Natural events such as volcanoes can trigger changes in weather patterns that can be hazardous