Natural Disasters Final - Pitt

factors for tornado initiation 

The general topography 

The local climate 

tornado region

regions of already severe thunderstorms 

areas where air is undisturbed by mountains 

tornado alley

Texas, Oklahoma, Kansas, Nebraska, Iowa, Missouri, Illinois

state where tornados are most rare

Alaska

state with most tornados

texas

state with most tornados - based on area ratio

florida

Is tornado alley changing with the changing climate? 

It is gradually shifting eastward

average tornado width

75 yards

average tornado track length (how long it is on the ground)

1-4 miles

average tornado time on ground

5 minutes

average tornado forward speed

25 mph

prime tornado season

spring to early summer (but this seems to be shifting with climate change)

prime time of day for tornados

Late afternoon to late evening - Time of maximum ground and atmospheric heating 

Tornado structure - how they form

Combinations of opposing wind patterns (dry and wet)

where do dry cooler winds come from (tornado formation)

the west

where do warm/wet winds come from (tornado formation)

the southeast originating in the golf of mexico 

energy source for thunderstorms

warm/wet air provides energy

Large thunderstorms pull warmer air upward from low levels 

rollers

winds form cyclonic rotation parallel to the ground

Large updrafts

an cause a roller to tip into a vertical position 

Tornado is born upon touchdown with the ground

Large storms can produce more than one tornado

Called tornado families or storms 

tornado swarm in 1974

caused damage to 13 states

148 tornados touched down in about 16 hours 

307 killed 

severe pressure drops for tornado formation

Inside a twister can be as low as 3” mercury (measured on a barometer)

tornado movement

generally SW to NE 

why do tornados move SW to NE?

Combination of the prevailing wind direction from the west 

The CCW rotation of the tornado

Fujita scale

Varies from EF0 to EF5 

Precise wind speed numbers are actually estimates based on damage after the storm and not measured directly during

EF0 tornado

light damage some damage to chimneys; branches broken off trees; shallow-rooted trees pushed over; sign boards damaged

EF1 Tornado

Moderate damage. Peels surface off roofs; mobile homes pushed off foundations or overturned; moving autos blown off roads

EF2 tornado

Considerable damage. Roofs torn off frame houses; mobile homes demolished; train cars overturned; large trees snapped or uprooted; light-object missiles generated; cars lifted off ground

EF3 tornado

Severe damage. Roofs and some walls torn off well-constructed houses; trains overturned; most trees in forest uprooted; heavy cars lifted off the ground and thrown.

EF4 tornado

Devastating damage. Well-constructed houses leveled; structures with weak foundations blown away some distance; cars thrown

EF5 tornado

Incredible damage. Strong frame houses leveled off foundations and swept away; automobile-sized missiles fly through the air in excess of 100 meters; trees debarked

early 1980s tornado monitoring

called TOTO

Designed to get swept up into a tornado and measure all the atmospheric parameters of a tornado from the inside

Scientists had to race to get ahead of a tornado and place the 400 pound cylinder squarely in its path

Never actually worked

storm prediction center

Monitors regional weather conditions every morning 

Issues a risk warning for severe weather later that day 

National severe storms lab

Use of doppler radar

Measures the frequency change of objects moving away from the antenna

Interpets mesocyclones

mobile doppler radar

Operated on a mobile platform to image nearby tornadic activity 

Can get much closer to the tornado to image it more clearly 

tornado mitigation

no practical efforts - Most injuries/death occur from flying objects or being picked up and thrown around

tornado mitigation - concrete lined rooms

can be placed in homes or backyards to keep residents safe from tornados - but does nothing to protect the house

2005 Hurricane season

Worst on record until 2020

including Epsilon and Zeta (at the “end of the season”), there were 27 named storms, surpassing the record of 21 set in 1933

normal hurricane season averages

10 named storms, 6 hurricanes and 2 major hurricanes

weaker hurricanes

impact larger areas

smaller hurricanes

have stronger winds but affect a smaller area 

hurricane damage overtime

Fatalities over time have gone down but insured property loss has skyrocketed 

Atlantic and pacific (eastern) storms are called ___

hurricanes

Pacific ocean (western) storms are called ___

typhoons

Indian Ocean storms are called ___

cyclones

hurricane storm stages

1. tropical wave

2. tropical depression or disturbance

3. tropical storm

4. hurricane

tropical wave

Initial low pressure disturbance

Unorganized

Moving west

Winds

tropical depression or disturbance

Moving mass of thunderstorms 

Starting to organize 

Winds

tropical storm

Gets named 

Distinct rotary/cyclonic motion 

Winds 39-74 mph

hurricane

Well defined circular structure

Central eye of low pressure first forms

Winds > 74mph

common Atlantic storm origin point

 off the coast of africa

hurricane season

from june-november 

conditions forming a tropical wave

calm wind patterns

Warm water (>80 degrees) - Provides large amounts of evaporation and fuel for the storm 

Vertical disturbance in the atmosphere (hurricane formation)

Caused by the interaction of westerly mid-lattidue winds with the easterly trade winds 

Allows a pathway to form for moisture transport from sea to upper atmosphere

Immense power generation for hurricane growth

Release of heat energy from the condensation of the water 

Global warming estimates for a 1 degree celsius increase in sea surface temp

hurricane positive feedback loop

stronger winds → more cylonic motion → draws up more moisture and heat from the sea → stronger winds 

hurricane structure

Rain bands of thunderstorms spiraling around a central (low pressure) eye 

moist, warm air is drawn up in the eye wall and within the spiriling arms 

hurricane eye

low pressure

Greatest winds are in the eye wall

Saffir-simpson scale (hurricanes)

Measured 1-5

Function of wind speed, storm surge, potential damage

hurricane storm surge

Large volume of rain/runoff prior to landfall of the hurricane

Two types: flood surge and ebb surge

flood surge

water brought onto the land by the storm

ebb surge

water floods back off the land to the sea

3 factors of a storm surge

Force of the waves 

Hydraulic lift (upward force) under structures

Reflected wave energy from other man-made structures 

Hurricane wind velocity (HWV)

the speed of the storm, the winds whipping around the eye

speed of the storm’s counter clockwise winds 

Storm center velocity (SCV)

speed that the storm is moving over ocean/land

influenced by the upper-level winds, regional temperature, other weather Patterns

HWV and SCV

both of these can combine to cause more damage

For a hurricane moving north in the NE quadrant

the HWV combines with the SCV

produces the most damaging winds

For a hurricane moving north in the SW quadrant of a hurricane

the SCV is subtracted from the HWV

results in the least damaging winds

hurricane Coast-parallel track

storm moves along the coast

weaker winds over the land and stronger winds over the ocean 

how land is affected in the hurricane coast-parallel track

by two storm surges: flood surge ahead of the storm and an ebb surge behind it

hurricane coast-parallel track damage

results in moderate-heavy damage along the coast

less damage further inland

hurricane coast-normal track

storm moves perpendicular to coast, moving from the water and onto the land

hurricane coast-normal track damage

strongest winds on the right side of the storm (HWV + SCV)

• produces a zone of higher damage off center to the right of the storm track

• less damage to the “left” side of the eye

hurricane yearly average

Since 6-7 hurricanes have formed in the north atlantic every year 

2 per year make landfall in the US

hurricane changes

Intensity has risen over the past 20 years

hurricane monitering

Visible and infrared satellite images

Planes flying through the storm center 

* Measure vertical structure, wind speeds, pressure, and temperature 

create storm track maps

hurricane Andrew damage

the costliest disaster in US history (until hurricane katrina)

• real estate development along the Florida coast in the 70s and 80s put lives and dollars at risk

• total damage = $27 billion

• 26 deaths directly attributable to Andrew

hurricane Andrew storm surge

most deaths associated with the storm surge and strong waves 

responsible for erosion and damage caused by floating debris

hurricane Katrina

the costliest and one of the deadliest hurricanes in American history

why was hurricane Katrina one of the worst?

waited too long to order city evacuation (many were trapped in the city from this)

slow response time from officials

flooding

when the volume of river/stream flow exceeds natural barriers and/or the levels of flood preparedness

natural causes of floods

heavy rain

dam failure

rapid snowmelt / ice jams 

deforestation

steep slopes

storm surges during tropical storms / hurricanes

flooding affects upstream

rapid rise and fall of water level

flooding affects downstream

slower rise and fall, but larger area affected

natural flooding factors

rainfall, infiltration rate (soil types), climate, season, vegetation 

anthropogenic flooding factors

urbanization, slope modification, timber industry, flood control measures, agriculture

use of river valleys

housing, agriculture, water supply, transportation routes

stream parameters: width

bank-to-bank distance

stream parameters: depth

distance from water surface to stream bed

stream parameters: length

distance from stream head to entrance into a larger water body 

stream parameters: discharge

volume / time

stream parameters: drainage basin

basic unit of surface water hydrology

stream parameters: divide

highest point between stream drainage basins 

stream flow

relationship between precipitation rate and infiltration rate

* determines how much water remains on the surface

infiltration capacity

capacity of a soil to absorb water

varies with soil type, soil condition, time of precipitation event

if precipitation rate > infiltration capacity

increased run off

flooding potential increases

Has high infiltration rates:

coarse soil

well-vegetated land

low soil moisture

porous topsoil

low infiltration rates

impermeable crusts

salt layers

cold weather 

Compaction

paved (impervious) surfaces

natural flood-related hazards

Erosion

Flooding 

human induced flood-related hazards

urbanization and modification of river valleys = Increase effects of the natural hazards