Climatic extremes

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EXTREME CLIMATIC (WEATHER) EVENTS
By
Prof. A. Balasubramanian
Centre for Advanced Studies in Earth Science
University of Mysore
Mysore-6

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Introduction:
The term climate describes the weather patterns of a
particular region over a longer period, usually 30 years or
more. Climate is an average pattern of weather for a particular
region. Weather is the state of the atmosphere with respect to
wind, temperature, cloudiness, moisture, pressure, etc.
The climate is a trend over an extended period of time.
The climate is the long-term average of varying weather
conditions in a region. Variation occasionally produces
extreme values of climate indicators such as temperature or
precipitation.

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Any shift in both average and extreme weather events over
time, with related impacts on human society, is an inevitable
result of the global climate change.
Climate Extreme (extreme weather or climate event) refers to
the occurrence of a value of a weather or climate variable
above (or below) a threshold value near the upper (or lower)
ends of the range of observed values of the variable.
Extreme weather and climate events, interacting with exposed
and vulnerable human and natural systems, can lead to
disasters.
Extreme weather
Extreme weather events, include unexpected, unusual,
unpredictable, severe or unseasonal weather conditions.

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This means that the weather is at the extremes of the
historical distribution. These types of extreme events are
based on a location’s recorded weather history.
These happen with reference to all the four seasons. The
climatic events are:
(i) Cold wave, Fog, Snow storms and Avalanches
(ii) Hailstorm, Thunderstorm and Dust storms
(iii) Heat wave
(iv) Tropical cyclones and Tidal waves,
(v) Floods, Heavy rain and Landslides, and
(vi) Droughts.
Some extreme weather and climate events have increased in
recent decades.

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The world has warmed. This global warming has triggered
many other changes to the Earth’s climate. Over the last 50
years, the world has seen increases in prolonged periods of
excessively high temperatures, heavy downpours, and in
some regions, severe floods and droughts.
Severe weather
Severe weather refers to any dangerous meteorological
phenomena with the potential to cause damage, serious social
disruption, or loss of human life. Extreme weather events
include high winds, hail, excessive precipitation, and
wildfires are forms.

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The effects of severe weather are thunderstorms, downbursts,
tornadoes, waterspouts, tropical cyclones, and extra-tropical
cyclones. Severe weather can occur under a variety of
situations, but the important characteristics are: a temperature
or moisture boundary, moisture, and (in the event of severe,
precipitation-based events) instability in the atmosphere.
The following are the list of extreme climatic events:
1. Cyclone
2. Tropical cyclone (also called a hurricane, typhoon, or
"cyclone")
3. Hurricane.
4. Windstorm (gradient pressure induced)

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5. Thunderstorm (hailstorm, downburst,
microburst/macroburst)
6. Winter storms
7. Fog
8. Heat wave
9. Cold wave
10. Supercell
11. Tornado
12. Waterspout
13. Blizzard
14. Ice storm
15. Derecho
16. Squall line.

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According to the World Meteorological Organization
(WMO), severe weather can be categorized into two groups:
general severe weather and localized severe weather.
Regional and seasonal severe weather phenomena include
blizzards (snowstorms), ice storms, and dust-storms.
The characteristics features of some of them are:
 Tornado: clouds, strong wind, rain, hail.
 Hurricane or cyclone: strong wind, heavy rain.
 Blizzard: heavy snow, ice, cold temperatures.
 Dust storm: strong winds, arid conditions.

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 Flood: heavy rainfall.
 Hail storm: cold or warm temperatures, rain, ice.
 Ice storm: freezing rain.
Downbursts and tornadoes are more localized and therefore
have a more limited geographic effect. These forms of
weather are classified as localized severe weather. The
severity is also dependent on the size of the geographic area
affected, whether it covers hundreds or thousands of square
kilometers.

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1. High winds:
High winds are known to cause damage, depending upon
their strength. Wind speeds as low as 23 knots (43 km/h)
may lead to power outages when tree branches fall and
disrupt power lines. Some species of trees are more
vulnerable to winds.
Trees with shallow roots are more prone to uproot, and brittle
trees such as eucalyptus, sea hibiscus, and avocado are more
prone to branch damage . Wind gusts may cause poorly
designed suspension bridges to sway.
Hurricane-force winds, can destroy mobile homes and
structurally damage buildings with foundations.

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Winds of this strength due to down slope winds off terrain
have been known to shatter windows and sandblast paint from
cars. Once winds exceed 135 knots (250 km/h) within strong
tropical cyclones and tornadoes, homes completely collapse,
and significant damage is done to larger buildings.
Total destruction to man-made structures occurs when winds
reach 175 knots (324 km/h).
2. Cyclone
A Cyclone is defined as any large system of winds that rotates
about a centre of low atmospheric pressure, with a speed
over 100 kmph.

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This swirling action happens in a counterclockwise direction
north of the Equator and in a clockwise direction to the south.
As the sun warms the oceans, evaporation and conduction
transfer heat to the atmosphere. This happens so rapidly that
the air and water temperatures rarely differ by more than a
degree F.
The water vapor generated by such evaporation is the driving
force for a tropical storm. As the vapor condenses into clouds
and precipitation, it releases enormous amounts of heat into
the cyclone. This has indicated a major point that cyclones
can not develop when the ocean temperature is below 24 deg.
C.

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The diameter of the ring of swirling winds may range from
500 to 1500 km. It is a highly dynamic movement and the
direction of its transgression is not precisely predictable.
The barometric pressure will be low at the centre of this mass
and that acts as a chimney through which air rises, expands,
cools dynamically and produces precipitation after
condensation.
Anticyclones have a flow opposite to that of cyclones--i.e., an
outward-spiraling motion, with the winds rotating clockwise
in the Northern Hemisphere and counterclockwise in the
Southern Hemisphere. They are usually not as strong as the
cyclonic storms and bring no rainfall.

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Both are regions of relatively low and high pressure,
respectively. They occur over several parts of the globe in a
variety of sizes ranging from larger to smaller dimensions.
3. Tornado
A tornado is a narrow, violently rotating column of air that
extends from the base of a thunderstorm to the ground.
Because wind is invisible, it is hard to see a tornado unless it
forms a condensation funnel made up of water droplets, dust
and debris. Tornadoes are the most violent of all
atmospheric storms.

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These dangerous rotating column of air in contact with both
the surface of the earth and the base of a cumulonimbus cloud
(thundercloud) or a cumulus cloud, in rare cases.
Tornadoes come in many sizes but typically form a visible
condensation funnel whose narrowest end reaches the earth
and surrounded by a cloud of debris and dust. Tornadoes'
wind speeds generally average between 40 miles per hour (64
km/h) and 110 miles per hour (180 km/h).
They are approximately 250 feet (76 m) across and travel a
few miles (kilometers) before dissipating.

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Some attain wind speeds in excess of 300 miles per hour (480
km/h), may stretch more than two miles (3.2 km) across, and
maintain contact with the ground for dozens of miles (more
than 100 km).
Tornadoes, despite being one of the most destructive weather
phenomena, are generally short-lived. A long-lived tornado
generally lasts no more than an hour, but some have been
known to last for 2 hours or longer.
Due to their relatively short duration, less information is
known about the development and formation of tornadoes.

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Tornadoes occur in many parts of the world, including
Australia, Europe, Africa, Asia, and South America. Even
New Zealand reports about 20 tornadoes each year. Two of
the highest concentrations of tornadoes outside the U.S. are
Argentina and Bangladesh.
About 1,200 tornadoes hit the U.S. every year. Since official
tornado records only date back to 1950, we do not know the
actual average number of tornadoes that occur each year. The
tornado spotting and reporting methods have also changed a
lot over the last several decades. Tornado season usually
refers to the time of year which sees the most tornadoes.
Tornadoes can also happen at any time of day or night.

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Tornadoes come from mainly two types of thunderstorms:
supercell and non-supercell. Tornadoes that come from
a supercell thunderstorm are the most common, and often the
most dangerous. A rotating updraft is a key to the
development of a supercell, and eventually a tornado.
4. Waterspout (non-supercell tornadoes)
Waterspouts are generally defined as tornadoes or non-
supercell tornadoes that develop over bodies of water.
Waterspouts typically do not do much damage because they
occur over open water, but they are capable of travelling over
land.

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Vegetation, weakly constructed buildings, and other
infrastructure may be damaged or destroyed by waterspouts.
Waterspouts do not generally last long over terrestrial
environments as the friction produced easily dissipates the
winds.
5. The Heat Burst( associated with strong gusty winds)
In meteorology, a heat burst is a rare atmospheric
phenomenon. It is characterized by gusty winds along with a
rapid increase in temperature and decrease in dew point
(moisture). It is usually accompanied by strong gusty winds,
extreme temperature changes, and an extreme decrease in
humidity.

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In general, heat bursts occur during the late spring and
summer seasons. During these times, thunderstorms tend to
generate day heating and lose their main energy during the
evening hours. Hence, heat bursts typically occur during
night-time and are associated with decaying thunderstorms.
The heat burst is created by vertical currents on the backside
of old outflow boundaries and squall lines where rainfall is
lacking.
Heat bursts generate significantly higher temperatures due to
the lack of rain-cooled air in their formation. Recorded
temperatures during heat bursts have reached well above 38
°C (100 °F), sometimes rising by 11 °C (20 °F) or more
within only a few minutes.

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6. Tropical cyclone
Tropical cyclones are rapidly rotating storm systems
characterized by a low-pressure center, a closed low-level
atmospheric circulation, strong winds, and a spiral
arrangement of thunderstorms that produce heavy rain. The
word "Tropical" refers to the geographical origin of these
systems, which form almost exclusively over tropical seas.
Tropical cyclones are accompanied by winds of extreme
violence.
Storms usually occur with cyclones. It is defined as a circular
storm with rotating wind speeds in excess of 32 metres per
second. The life span of a tropical cyclone is on an average,
six to nine days until it enters the land.

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No tropical cyclone follows the same track. Very high winds
can be caused by mature tropical cyclones (called hurricanes
in the United States and Canada and typhoons in eastern
Asia).
A tropical cyclone's heavy surf created by such winds may
cause harm to marine life either close to or upon the surface
of the water, such as coral reefs. Coastal regions may
receive significant damage from a tropical cyclone while
inland regions are relatively safe from the strong winds, due
to their rapid dissipation over land. However, severe
flooding can occur even far inland because of high amounts
of rain from tropical cyclones and their remnants.

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The strong rotating winds of a tropical cyclone are a result of
the conservation of angular momentum imparted by the
Earth's rotation as air flows inwards toward the axis of
rotation. As a result, they rarely form within 5° of the equator.
Tropical cyclones are almost unknown in the South Atlantic
due to a consistently strong wind shear and a weak
Intertropical Convergence Zone.
Coastal regions are particularly vulnerable to the impact of a
tropical cyclone, compared to inland regions. The primary
energy source for these storms is warm ocean waters,
therefore these forms are typically strongest when over or
near water, and weaken quite rapidly over land.

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A tropical cyclone is a storm system characterized by a low-
pressure center and numerous thunderstorms that produce
strong winds and flooding rain.
A tropical cyclone feeds on heat released when moist air
rises, resulting in condensation of water vapour contained in
the moist air. Tropical cyclones may produce torrential rain,
high waves, and damaging storm surge. Heavy rains produce
significant inland flooding.
Storm surges may produce extensive coastal flooding up to 40
kilometres (25 mi) from the coastline. Although cyclones
take an enormous toll in lives and personal property, they are
also important factors in the precipitation regimes of areas
they affect.

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7. Typhoons (low-pressure tropical storms):
A Typhoon is a violent, low-pressure tropical storm that
occurs in the western Pacific Ocean.
They are similar to hurricanes, beginning near the equator
and move westward. They advance slowly, usually at about
15 to 25 kilometres per hour speed. The circular winds
around the centre are very strong, often reaching speeds of
240 kilometres per hour.
The diameter of a typhoon can be as large as 480 kilometres.
Typhoons are associated with heavy rains and powerful winds
causing severe land and property damage and loss of life.
The destructive rush of seawater, called a storm surge, often
accompanies a typhoon as it moves onto coastal lands.

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One of the Cyclonic storm surges which occurred in the east
coast of India during 1977, was reported to have been 5.7 m
high, 80 km long, 16 km wide with a speed of 190kmph.
8. Hurricanes (Superstorms):
Hurricanes are dangerous storms that affect millions of
people each year. Hurricane Katrina in 2005, Hurricane
Irene in 2011 and Superstorm Sandy in 2012, did major
damage and killed many people. A hurricane is like a giant,
self-sustaining heat engine - it keeps itself going unless the
process is stopped.
Condensation of the ocean water releases heat, which draws
moist air from the ocean up into the eye of the storm.

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The moist air cools, which means there is more condensation,
which leads to more heat being generated. This brings
additional moist air up from the ocean, which cools and
condenses.
Hurricanes don't develop out of thin air, though; they begin as
small storms that grow into larger, more dangerous ones.
In its infancy, a hurricane starts as a tropical depression,
which is a tropical spinning storm with wind speeds less than
39 mph. As it grows into adolescence, the tropical depression
develops into a tropical storm, which is a tropical spinning
storm with wind speeds between 40 and 73 mph.

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If it develops into a full adult storm, it becomes a hurricane,
which is a tropical spinning storm with wind speeds above 74
mph. Hurricanes don't continue forever; they are eventually
stopped.
Once it moves over land, the hurricane runs out of fuel
because it runs out of water to perpetuate the cycle. The
ocean is like a food source for a hurricane - it provides it with
energy to grow big and strong.
Once over land, though, the food source runs out and the
storm is deprived of the energy it needs to keep going,
essentially starving to death. Hurricanes are huge heat
engines that run on warm water, capable of producing
roughly 200 times the entire world's electrical generating
capacity with rain and cloud formation alone.

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Their power source is the sun, which heats up tropical sea
water all spring to have the engines building and revving
themselves by early summer.
9. Thunderstorms:
A thunderstorm is a rain shower during which you hear
thunder. Since, the thunder comes from lightning, all
thunderstorms have lightning. A thunderstorm is the result of
convection. A thunderstorm is classified as “severe” when it
contains one or more of the following: hail one inch or
greater, winds gusting in excess of 50 knots (57.5 mph), or a
tornado.

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Thunderstorms are most likely to occur in the spring and
summer months and during the afternoon and evening hours,
but they can occur year-round and at all hours.
Thunderstorms frequently occur in the late afternoon and at
night in the plains states.
Three basic ingredients are required for a thunderstorm to
form: moisture, a rising unstable air (air that keeps rising
when given a nudge), and a lifting mechanism to provide the
“nudge.”
The sun heats the surface of the earth, which warms the air
above it. If this warm surface air is forced to rise , it will
continue to rise as long as it weighs less and stays warmer
than the air around it.

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As the air rises, it transfers heat from the surface of the earth
to the upper levels of the atmosphere (the process of
convection). The water vapour which it contain, s begins to
cool, releases the heat, condenses and forms a cloud. The
cloud eventually grows upward into areas where the
temperature is below freezing.
As a storm rises into freezing air, different types of ice
particles can be created from freezing liquid drops. The ice
particles can grow by condensing vapor (like frost) and by
collecting smaller liquid drops that haven't frozen yet (a state
called "supercooled"). When two ice particles collide, they
usually bounce off each other, but one particle can rip off a
little bit of ice from the other one and grab some electric
charge.

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Lots of these collisions build up big regions of electric
charges to cause a bolt of lightning, which creates the sound
waves we hear as thunder. Thunderstorms are a great way
for the atmosphere to release energy.
The Thunderstorm Life Cycle:
Thunderstorms have three stages in their life cycle: The
developing stage, the mature stage, and the dissipating stage.
The developing stage of a thunderstorm is marked by a
cumulus cloud that is being pushed upward by a rising
column of air (updraft). The cumulus cloud soon looks like a
tower (called towering cumulus) as the updraft continues to
develop.

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There is little to no rain during this stage but occasional
lightning. The thunderstorm enters the mature stage when the
updraft continues to feed the storm, but precipitation begins
to fall out of the storm, creating a downdraft (a column of air
pushing downward).
When the downdraft and rain-cooled air spreads out along the
ground it forms a gust front, or a line of gusty winds.
The mature stage is the most likely time for hail, heavy rain,
frequent lightning, strong winds, and tornadoes.
Eventually, a large amount of precipitation is produced and
the updraft is overcome by the downdraft beginning the
dissipating stage.

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Rainfall decreases in intensity, but lightning remains a
danger. Often called “popcorn” convection, single-cell
thunderstorms are small, brief, weak storms that grow and
die within an hour or so.
They are typically driven by heating on a summer afternoon.
Single-cell storms may produce brief heavy rain and
lightning.
Lightning is a sudden electrostatic discharge that occurs
typically during a thunderstorm. This discharge occurs
between electrically charged regions of a cloud (called intra-
cloud lightning or IC), between two clouds (CC lightning), or
between a cloud and the ground (CG lightning).

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A multi-cell storm is a common, garden-variety
thunderstorm in which new updrafts form along the leading
edge of rain-cooled air (the gust front). Individual cells
usually last 30 to 60 minutes, while the system as a whole
may last for many hours. A supercell is a long-lived (greater
than 1 hour) and highly organized storm feeding off an
updraft (a rising current of air) that is tilted and rotating.
10. Downburst(Thunderstorms)
Downbursts are created within thunderstorms by significantly
rain-cooled air, which, upon reaching ground level, spreads
out in all directions and produce strong winds.

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"Dry downbursts" are associated with thunderstorms with
very little precipitation, while wet downbursts are generated
by thunderstorms with large amounts of rainfall.
Microbursts are very small downbursts with winds that
extend up to 2.5 miles (4 km) from their source, while
macrobursts are large-scale downbursts with winds that
extend in excess of 2.5 miles (4 km).
11. Squall line(Thunderstorms)
A squall line is an elongated line of severe thunderstorms that
can form along or ahead of a cold front.

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A squall line (also known as a quasi-linear convective system
or QLCS) is a line of thunderstorms forming along or ahead
of a cold front. In the early 20th century, the term was used as
a synonym for cold front.
The squall line typically contains heavy precipitation, hail,
frequent lightning, strong straight line winds, and possibly
tornadoes or waterspouts.
Squall lines often cause severe straight-line wind damage, and
most non-tornadic wind damage is caused from squall lines.
Squall lines are associated with sharp wind shear, including
sudden, marked shifts in wind direction and speed.

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12. Strong extratropical cyclones
Cyclones of a somewhat different character occur closer to
the Equator, forming in latitudes 10 to 15 N and S over the
oceans. They are an essential part of the mechanism by which
the excess heat received from the Sun in the equatorial belt is
conveyed toward higher latitudes. These higher latitudes
radiate more heat to space than they receive from the Sun.
Strong horizontal temperature gradients are responsible for
the formation of cyclones.
These are known as the tropical cyclones. Those cyclones
that form outside the equatorial belt are known as extra-
tropical cyclones.

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The name of cyclone differs from region to region. The
extratropical cyclones range from nearly 1,000 to 4,000
kilometres.
Whereas, the tropical cyclones measure only about 100 to
500 kilometres in diameter. They are more violent than those
occurring in the midlatitudes and can cause considerable
damage. These are transient cyclones.
They are the most abundant phenomena and exert influence
on the broadest scale, affecting the largest percentage of the
Earth's surface. It has an impact on the day-to-day weather
changes.

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The life cycle of these events is typically several days, during
which the cyclone may travel from several hundred to a few
thousand kilometres. In its path and wake occur dramatic
weather changes.
13. Dust storm
An unusual form of windstorm that is characterized by the
existence of large quantities of sand and dust particles carried
by the wind. Dust storms frequently develop during periods
of droughts, or over arid and semi-arid regions. Dust storms
have numerous hazards and are capable of causing deaths.
Visibility may be reduced dramatically, so risks of vehicle
and aircraft crashes are possible.

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Additionally, the particulates may reduce oxygen intake by
the lungs, potentially resulting in suffocation. Damage can
also be inflicted upon the eyes due to abrasion.
Dust storms can many issues for agricultural industries as
well. Soil erosion is one of the most common hazards and
decreases arable lands. Dust and sand particles can cause
severe weathering of buildings and rock formations. Nearby
bodies of water may be polluted by settling dust and sand,
killing aquatic organisms.
Decrease in exposure to sunlight can affect plant growth, as
well as decrease in infrared radiation may cause decreased
temperatures.

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14. Storm surge
Storm surge is often the greatest threat to life and property
from a tropical cyclone, and it can occur at different times
and at different locations from a storm’s hazardous winds.
The danger of life-threatening inundation from rising water
moving inland from the shoreline somewhere within the
specified area, generally within 36 hours, in association with
an ongoing or potential tropical cyclone, a subtropical
cyclone, or a post-tropical cyclone.

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15. Wildfires
The most common cause of wildfires varies throughout the
world. In the United States, Canada, and Northwest China,
lightning is the major source of ignition. In other parts of the
world, human involvement is a major contributor. Wildfires
can be attributed to human activities such as animal
husbandry, agriculture, and land-conversion burning. Human
carelessness is a major cause of wildfires in China and in the
Mediterranean Basin.
Wildfires have a rapid forward rate of spread (FROS) when
burning through dense, uninterrupted fuels.

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They can move as fast as 10.8 kilometers per hour (6.7 mph)
in forests and 22 kilometers per hour (14 mph) in grasslands.
Torching and fires in tree canopies encourage spotting, and
dry ground fuels that surround a wildfire are especially
vulnerable to ignition from firebrands. Spotting can create
spot fires as hot embers and firebrands ignite fuels downwind
from the fire.
16. Hail
Any form of thunderstorm that produces precipitating
hailstones is known as a hailstorm.

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Hailstorms are generally capable of developing in any
geographic area where thunderclouds (cumulonimbus) are
present, although they are most frequent in tropical and
monsoon regions.
The updrafts and downdrafts within cumulonimbus clouds
cause water molecules to freeze and solidify, creating
hailstones and other forms of solid precipitation.
Due to their larger density, these hailstones become heavy
enough to overcome the density of the cloud and fall towards
the ground. The downdrafts in cumulonimbus clouds can
also cause increases in the speed of the falling hailstones.
The term "hailstorm" is usually used to describe the existence
of significant quantities or size of hailstones.

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Hailstones can cause serious damage, notably to automobiles,
aircraft, skylights, glass-roofed structures, livestock, and
crops.
17. Heavy rainfall and flooding
Heavy rainfall can lead to a number of hazards, most of
which are floods or hazards resulting from floods. Floods
are extreme weather events that have had major effects at
different times and in different locations. Major floods
outside the normal pattern of flooding have occurred, in many
countries.

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Floods are responsible for the deaths of many people and
livestock, and it also caused damage to homes , livelihoods
and infrastructure, in many parts of the world.
Flooding is the inundation of areas that are not normally
under water.
It is typically divided into three classes:
River flooding, which relates to rivers rising outside their
normal banks; flash flooding, which is the process where a
landscape, often in urban and arid environments, is subjected
to rapid floods and coastal flooding, which can be caused by
strong winds from tropical or non-tropical cyclones.

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Meteorologically, excessive rains occur within a plume of air
with high amounts of moisture (also known as an atmospheric
river) which is directed around an upper level cold-core low
or a tropical cyclone.
18. Flash floods
Flash floods are floods that happen as a result of intense
rainfall in a localised area and they usually drain away quite
quickly. Flash flooding can frequently occur in slow-moving
thunderstorms and are usually caused by the heavy liquid
precipitation that accompanies it.

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Flash floods are most common in dense populated urban
environments, where less plants and bodies of water are
presented to absorb and contain the extra water. If a large
amount of rain falls onto the land in a short time and it cannot
soak into (infiltrate) the soil, the water runs downhill across
the land surface.
This heavy flow of surface run-off can cause a flash flood.
There are many factors that increase the risk of flash floods
including changes in land use and poor soil permeability.
When forests and grasslands are removed for the construction
of roads and buildings, permeable soil is replaced by hard
surfaces such as concrete. This reduces the infiltration of
water into the ground and increases run-off, making flooding
more effective.

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Flash flooding can be hazardous to small infrastructure, such
as bridges, and weakly constructed buildings.
Plants and crops in agricultural areas can be destroyed and
devastated by the force of raging water. Automobiles parked
within experiencing areas can also be displaced.
Soil erosion can occur as well, exposing risks of landslide
phenomena.
Like all forms of flooding phenomenon, flash flooding can
also spread and produce waterborne and insect-borne diseases
cause by microorganisms.

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19. Monsoons
Seasonal wind shifts lead to long-lasting wet seasons which
produce the bulk of annual precipitation. Widespread
flooding occurs if rainfall is excessive, which can lead to
landslides and mudflows in mountainous areas. Floods cause
rivers to exceed their capacity with nearby buildings
becoming submerged.
Flood waters that occur during monsoon seasons can often
host numerous protozoa, bacterial, and viral microorganisms.
Mosquitoes and flies will lay their eggs within the
contaminated bodies of water.

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These disease agents may cause infections of food-borne and
waterborne diseases. Diseases associated with exposure to
flood waters include malaria, cholera, typhoid, hepatitis A,
and the common cold.
20. Severe winter weather
When extratropical cyclones deposit heavy, wet snow with a
snow-water equivalent (SWE) significant damage may occur
on a scale usually associated with strong tropical cyclones.
An avalanche can occur with a sudden thermal or mechanical
impact on snow that has accumulated on a mountain, which
causes the snow to rush downhill suddenly.

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The strong winds associated with blizzards create wind chill
that can result in frostbites and hypothermia.
The strong winds present in blizzards are capable of
damaging plants and may cause power outages, frozen pipes,
and cut off fuel linesConditions within blizzards often include
large quantities of blowing snow and strong winds which may
significantly reduce visibility.
21. Ice storm
Ice storms are also known as a Silver storm, referring to the
color of the freezing precipitation.

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Ice storms are caused by liquid precipitation which freezes
upon cold surfaces and leads to the gradual development of a
thickening layer of ice. The accumulations of ice during the
storm can be extremely destructive.
Trees and vegetation can be destroyed and in turn may bring
down power lines, causing the loss of heat and
communication lines.
Roofs of buildings and automobiles may be severely
damaged. Gas pipes can become frozen or even damaged
causing gas leaks. Avalanches may develop due to the extra
weight of the ice present. Visibility can be reduced
dramatically.

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The aftermath of an ice storm may result in severe flooding
due to sudden thawing, with large quantities of displaced
water, especially near lakes, rivers, and bodies of water.
22. Heat and drought
Another form of severe weather is drought, which is a
prolonged period of persistently dry weather (that is, absence
of precipitation). Drought is the absence of rain for an
extended period, often for a season or more. Climate change
is associated with the significant reduction in rainfall and
increase in droughts.
Droughts have caused loss of human life, livestock and
property, as well as it leads to the migration of people.

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Drought affects agriculture by damaging crops and decreasing
crop yield. Drought causes food shortages not only in rural
areas but also in urban environments. In the worst periods of
drought there may be widespread famine, when the extreme
shortage of food results in many deaths.
Although droughts do not develop or progress as quickly as
other forms of severe weather, their effects can be just as
deadly; in fact, droughts are classified and measured based
upon these effects.
Droughts have a variety of severe effects; they can cause
crops to fail and they can severely deplete water resources,
sometimes interfering with human life. In addition to the
other severe effects, the dry conditions caused by droughts
also significantly increase the risk of wildfires.

57
23. Heat waves
Heatwaves are prolonged periods of unusually hot weather,
which may or may not be accompanied by high humidity. The
World Meteorological Organization definition of
a heatwave is ‘when the daily maximum temperature on
more than five consecutive days exceeds the average
maximum temperature by 5 °C. The perception of a heatwave
varies geographically because it is measured relative to the
average temperature in that area. They are extremely
dangerous to humans and animals.

58
The average total number of heat-related fatalities each year
is higher than the combined total fatalities for floods,
tornadoes, lightning strikes, and hurricanes.
24. El Niño and La Niña
There are two natural climate cycles that can affect the
location and frequency of extreme weather events around the
world. The rise in sea temperature will have widespread
effects on ocean currents, particularly in the Pacific Ocean.
When the Pacific Ocean is unusually warm, it generates a
climate cycle known as El Niño (‘little boy’ in Spanish);
when the ocean temperature is unusually cool, the climate
cycle is called La Niña (‘little girl’).

59
El Niño and La Niña have opposite effects on the climate.
However, they influence the route and speed of major
airstreams and alter the pattern of rainfall around the world.
Due to this , some regions are wetter than average and others
are drier.
Extreme high and low temperatures can have important
impacts on human society, including increased energy use
(for heating and cooling buildings), damage to infrastructure
(e.g., burst pipes), and heat- and cold-related illnesses.

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25. Derecho
A derecho (from Spanish: "derecho" meaning "straight") is a
widespread and long-lived, violent convectively induced
straight-line windstorm. It is associated with a fast-moving
band of severe thunderstorms, usually taking the form of a
bow echo. Derechos blow in the direction of movement of
their associated storms, similar to a gust front, except that the
wind is sustained and generally increases in strength behind
the "gust" front. It is a warm weather phenomenon. It occurs
mostly in summer, between May and August in the Northern
hemisphere. They can occur at any time of the year and occur
as frequently at night as in the daylight hours.

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Conclusion:
Most of the weather events are now influenced by climate
change. All weather, now, gets developed in a different
atmospheric condition than before. While natural variability
continues to play a key role in extreme weather, climate
change has shifted the odds and changed the natural limits,
making certain types of extreme weather more frequent and
more intense. As the climate has warmed, some types of
extreme weather have become more frequent and severe in
recent decades, with increases in extreme heat, intense
precipitation, and severe drought. Heat waves are longer and
hotter.

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Heavy rains and flooding are more frequent. In a wide swing
between extremes, drought, too, is more intense and more
widespread.
Even a small increase in the average temperature can leads to
a big change in the weather conditions.
Substantial changes in the frequency and intensity of extreme
events can result from a relatively small shift in the average
distribution of temperatures, pressure, humidity, precipitation,
or other climate variables.

Climatic extremes

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