Severe Storm Hazards

1. Severe Storm Hazards

2. Severe Storm Hazards • Smith Ch 9 • Tectonic hazards: usually localised • Storm hazards: potentially affect large areas

3. Severe Storm Hazards • 1980s, annual averages: • 30,000 deaths worldwide • US$2-3 Bn in damage

4. Why storms happen • Tropics get hot, poles get cold • Ocean currents, air masses • move heat and moisture toward poles, cold water, cold air toward tropics • Ocean currents move most of the heat

5. Why storms happen • Air masses mix and collide • Hot moist air rises over cold • high winds, precipitation • The greater the temperature contrast the more dramatic the movement • severe storms

6. Why storms happen • All the fault of Boyle’s law • Pressure = Volume * Temperature

7. Scale • Small scale (time, space): • Tornadoes, Hailstorms • Medium scale (time, space) • Topical cyclones, Frontal systems

8. Cyclicity • Seasonal recurrence • Tropical cyclones, tornadoes, the monsoon • Episodic • El Nino/La Nina (ENSO)

9. ENSO • El Nino Southern Oscillation • Occurs every 2-7 years • Southern Pacific ocean currents and air masses temporarily reverse direction of circulation

10. Normal year

11. El Nino year

12. El Nino Year • Heavy rainfall & floods on S. American coast • Absence of cold current brings collapse of marine fishery • Australia, Indonesia, New Zealand face drought instead of wet season • May reach other regions: • drought/storms in California

13. 1983 El Nino drought Australia

14. California after 1997-8 El Nino

16. Hurricane Pauline Oct 1997

17. Tropical Cyclones • Responsible for about half of severe-storm deathtoll • Hot, moist tropical surface air penetrates to top of troposphere

18. Tropical Cyclones • a.k.a. Hurricanes, Typhoons, Tropical cyclones • Tropical storms (if smallish)

19. Tropical Cyclones • Chain reaction storms • Rising moist air 10-12 km in height • condensing moisture releases latent heat keeping rising air warm • continues to rise • Produces low pressure at sea level, bringing in more moist air

21. Tropical Cyclones • Only form over tropical oceans • requires heat and moisture • away from cold ocean currents • tend to decay over land • Vortex required to generate storm structure • at least 5 degrees latitude away from equator for sufficient coriolis force • Centre of vortex, the eye, is calm and dry

23. Hurricane Winnie

24. Hurricane Gilbert

27. Tropical Cyclones • Strong winds (perhaps 180 km/h) • structural damage on land • Heavy rainfall (250 mm in 12 hours?) • landslides, freshwater flooding • Storm surge (DennisFloyd) • kills most of the storm’s victims • low pressure and storm-built waves flood low-lying coasts

28. Hurricane Juan 1985 Richmond Va

29. Hurricane Hazel 1954 • Fairglen Rd Weston ON

30. Clarence St Woodbridge

31. Raymore Dr Weston

32. Royal York Rd after Hazel

36. Holland Marsh

37. Hurricane storm surge

39. Hurricane Debby

40. Saffir-Simpson Scale • Scale for hurricanes • Range of 1-5 • 1: winds 140 km/h, 1.4 m storm surge • 5: winds 250 km/h winds 6 m storm surge

41. Tropical Cyclones • 86 tropical storms annually • 46 Category 1-2 hurricanes • 20 Category 3-5 hurricanes

42. Tropical Cyclones • Threatens about 15% of global population

43. Vulnerability • Dense population on low-lying land • Bangaladesh

44. Bangaladesh • 1970 Category 5 cyclone kills 300,000 • 1991 Category 5 cyclone kills 200,000 10M homeless • 1998 Cyclone makes 25% of population homeless • reported on page A26 of Toronto Star

45. Bangaladesh 1985

46. Galveston TX 1900

47. Galveston TX 1900

48. Vulnerability • Small nations • Disrupts national economy

49. Hurricane Mitch 1998 in Honduras • Category 5 storm, 6000 dead • Destroyed • 60% of bridges • 25% of schools • 50% of commercial cropland • 60% of GDP • Honduras the 2nd poorest nation in the Americas

50. Hurricane Mitch 1998