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Severe Storm Hazards. Severe Storm Hazards. Smith Ch 9 Tectonic hazards: usually localised Storm hazards: potentially affect large areas. Severe Storm Hazards. 1980s, annual averages: 30,000 deaths worldwide US$2-3 Bn in damage. Why storms happen. Tropics get hot, poles get cold
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Severe Storm Hazards • Smith Ch 9 • Tectonic hazards: usually localised • Storm hazards: potentially affect large areas
Severe Storm Hazards • 1980s, annual averages: • 30,000 deaths worldwide • US$2-3 Bn in damage
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
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
Why storms happen • All the fault of Boyle’s law • Pressure = Volume * Temperature
Scale • Small scale (time, space): • Tornadoes, Hailstorms • Medium scale (time, space) • Topical cyclones, Frontal systems
Cyclicity • Seasonal recurrence • Tropical cyclones, tornadoes, the monsoon • Episodic • El Nino/La Nina (ENSO)
ENSO • El Nino Southern Oscillation • Occurs every 2-7 years • Southern Pacific ocean currents and air masses temporarily reverse direction of circulation
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
Tropical Cyclones • Responsible for about half of severe-storm deathtoll • Hot, moist tropical surface air penetrates to top of troposphere
Tropical Cyclones • a.k.a. Hurricanes, Typhoons, Tropical cyclones • Tropical storms (if smallish)
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
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
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
Hurricane Hazel 1954 • Fairglen Rd Weston ON
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
Tropical Cyclones • 86 tropical storms annually • 46 Category 1-2 hurricanes • 20 Category 3-5 hurricanes
Tropical Cyclones • Threatens about 15% of global population
Vulnerability • Dense population on low-lying land • Bangaladesh
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
Vulnerability • Small nations • Disrupts national economy
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