Extreme Weather Events

Extreme weather events are weather conditions that are different from the normal weather in a particular region.
They include exceptional winds, heavy rainfall, drought, heat and cold.
Climate change greatly increases the amount of extreme weather events.
Heat waves and wildfires are becoming particularly frequent and intense.
We must prepare for more variable weather conditions, unpredictable climates and extreme weather.
This can be done through improved forecasting and evacuation systems to reduce damage and slowing down climate change to prevent worsening conditions.
Deaths caused by extreme weather events are the highest in developing countries, whereas there are greater economic losses in developed countries.
Earthquakes and hurricanes are the deadliest and costliest natural hazards.
However, they only occur in certain regions.

Wind Formation

Wind is created when air flows from high pressure to low pressure.
High pressure areas are formed by descending cold air.
Low pressure, on the other hand, is created when air heated by the sun rises.

Low vs High Pressure

In low pressure areas, air from the troposphere cools down and condenses into droplets, leading to clouds and rain.
In high pressure areas are generally cool and dry.
The weather is usually sunny due to clear skies.

Coriolis Effect

The wind direction is also affected by the Coriolis effect, which is caused by the rotation of the Earth.
Causes winds to turn right in the northern hemisphere and to the left in the southern hemisphere.
The Coriolis effect causes the wind to blow diagonally towards the center of low pressure.
The equator is unaffected by the Coriolis effect.

Trade Winds

The trade winds are fairly steady winds blowing towards the equator.
They flow from high pressure centers of the horse latitudes (located 30 degrees north and south of the equator) to low pressure centers of the equator.

Polar Front

The polar front is the zone in northern European latitudes where the cold air mass from the polar region meets the warm air mass from the tropics.
The collision of these two air masses can cause storms and fast winds.
The upwelling of warm and cold air creates low pressure centers.
The front moves northward in summer and southward in winter

As the cold, arctic air mass spreads over a warm ocean area in summer, the air warmed by the sea rises strongly above the cold air, creating strong low pressure.
The greater the temperature difference at the polar front boundary, the stronger the storms that develop.
As a result, storms in the North Atlantic are mainly concentrated in late autumn and early winter.
These storms are called polar front storms or mid-latitude storms.
The storms subside as they move from the sea to the land, but in early winter when the Baltic Sea melt, they can intensify after crossing Sweden.
These storms have an average wind speed of 21 meters per second, less than the minimum for hurricanes, which is about 33 m/s.

Tropical Cyclones

Tropical cyclones are rapidly rotating storm systems.
They are called hurricanes in the Americas, typhoons in East Asia and tropical cyclones in the Indian Ocean.
They get their energy from warm seawater.
When sea surface temperatures are above 26–27 °C, a very strong upward air current can develop as water evaporates in large quantities.
The resulting low pressure zone fills with air from elsewhere, forming strong winds that begin to spin around due to the Coriolis effect.
Hurricanes thus cannot occur at the equator due to the weak Coriolis effect.
Hurricanes generally occur around 5 and 30 degrees north or south.
Category 1 hurricanes have a wind speed of about 33m/s and category 5 hurricanes have wind speeds of over 70m/s.
The wind speed is highest near the eye of the hurricane.
However the center, or the "eye" is calm, but also has the highest barometric pressure (air pressure).
Tropical cyclones can form in the Atlantic and Indian Oceans during the late summer and early autumn.
In the northern hemisphere, hurricanes occur between August and October.
In the southern hemisphere they occur between February and April.
Typhoons occur all throughout the year in the western Pacific Ocean.
Tropical cyclones last a few days (6 on average) and can reach sizes of even over 1000 kilometers in diameter.
Their height can range from 10 to 15 kilometers.
They move with the trade winds over water at speeds of about 20 to 50 kilometers per hour.
They subside once they reach the mainland or a colder sea area.

Tornadoes

Tornadoes are strong, upward-swirling winds that occur near the front of a thunderstorm.
These thunderstorms are particularly common in the polar front in late summer.
The temperature difference near the boundary of the cold front can be exceptionally high.
However, tornadoes can occur anywhere where there is a high enough difference between air pressures.
Tornadoes can be very fast but usually only last a few minutes to an hour.
Their wind speeds have been recorded to be anywhere from 70 to 500 kilometers an hour.
Their diameter is usually less than a kilometer and they occur on the edge of a large storm cloud.
The diameter of the tip can range from a few meters to a few hundred.
They form on land but can occur over water, in which case they are called waterspouts.
The strongest tornadoes occur in the tornado belt or tornado alley of the Midwestern United States.
In this area warm, moist air from the Gulf of Mexico collides with the cold air mass from Canada.
The flat terrain of this area also allows tornadoes to form better.

Forming

Powerful thunderstorms and tornadoes form where cold air and warm air masses meet.
In these areas, tornadoes occur from spring to autumn in favorable conditions.
Tornadoes can also occur in the storms of tropical cyclones.
Much weaker tornadoes can be sometimes encountered in Europe, these are called trombis.
They occur less often in Europe. For example there are about 20 per year in Finland compared to about 1200 a year in the United States.

Downbursts

Heavy downpour and a downward flow of air.
Strong cold winds formed in a thundercloud.
Heavy downpour causes a downward flow of cold air inside a cloud.
When it hits the ground it turns horizontally and can speed up to 50m/s for a few minutes in some places.

Flooding

Temporary overflow of water on normally dry land.
Can occur from excessive rainfall, tsunamis or overflow of rivers.
Flooding is a very common but a extremely dangerous phenomenon.
It causes half of all casualties from natural disasters.
Overflow from rivers or rainy seasons are common reasons for flooding.
Lakes can help prevent flooding as they act as water reservoirs.

Damages Caused by Flooding

Flooding can destroy housing and property.
Strong flooding can destroy infrastructure and resources, leading to a famine in some areas.
They can spread dangerous chemicals and diseases.
Flooding is additionally more dangerous as most megacities are built next to rivers that are prone to flooding.
Flooding mostly threatens poorer countries, as they have a harder time preparing and recovering from floods and are more susceptible to disease and famine.
People often live near flooding rivers as the areas that flood are very fertile and good for cultivation, which puts them in risk of flooding.

Causes

Climate change leads to more heavy rainfall and floods
Other extreme weather events such as hurricanes or tsunamis
Poor drainage
Location
Strong rainfall, for example during monsoon seasons
Deforestation (land erodes instead of absorbing water)
Urbanization and the paved surfaces (land cannot absorb water)
Groundwater flooding
High tides
Damn breaches
Heavy snow cover melting
Low elevation

River Deltas

Most rivers end in wide cone shapes called deltas.
They occur when rivers and oceans connect.
River deltas are prone to flooding, especially with increased rainfall.
These can lead to fertile plains but also dangerous areas for living.

Effects

Contaminating clean water sources
Spreading disease
Damaging buildings and infrastructure
Damaging crops
Deaths from drowning and famine

Flood Protection

Dams and river control reservoirs
Land use far from populated areas
Measuring water flows to predict floods

Heat Waves

Hot spells, or heat waves are times of abnormally high temperatures.
They can cause heat strokes and heart attacks, especially among the elderly or ill.
Especially dangerous in poorer countries where most people lack air conditioning.
In other areas, demand for cooling in living spaces can even overwhelm electrical grids.

Drought

Long-term drought is one of the most damaging extreme weather events.
It is caused by lack of rainfall and can cause water use restrictions and loss of crops and livestock.
In the Sahel region, droughts have led to famine in recent years. The El Niño phenomenon has also caused severe droughts in South-East Asia, Australia and the east coast of Africa.

Wildfires

A combination of heat and drought causes wildfires.
They are part of the natural environmental cycle in some regions, but now damaging and dangerous wildfires are becoming more and more common worldwide.
They are often triggered by a lightning strike, which lights up dried vegetation.
However, human interference also causes many wildfires.
Controlled burns in some areas are used to increase nutrient contents of soil.
Improved firefighting methods can somewhat combat wildfires.

Heavy Snowfall

Cold weather and heavy snowfall can be dangerous if not prepared for.
They can cause deaths by hypothermia or lock down small towns or neighborhoods due to the amount of snow.
Can cause power cuts and traffic problems.
They also can lead to avalanches.
It is generally a problem in areas where snowfall and cold are rare, leading people to be unprepared.

Heavy Rainfall

One millimeter of precipitation means that a 1 mm layer of water, or one liter of water, accumulates on one square meter of Earth's surface.
What is considered heavy rainfall differs in countries.
It is defined by a certain amount of mm of water in a certain amount of time.
Heavy rainfall usually isn't problematic with proper preparedness.
However, some extreme cases can cause flash flooding.
The monsoon rains of South Asia are best known for their heavy rainfall.

Storm Damage

High winds can damage trees and structures.
Damage to power lines can cause power cuts.
Storms generally lead to economic losses but can also take lives in unprepared or highly populated areas.
Storms can cause damage to crops.
Heavy rainfall and flooding are usually the main problems caused by large storms.
Weather satellites can be used to monitor low pressure areas and possible storms.
These can allow for evacuations before a storm hits.
Some extreme weather events such as tornadoes and downbursts are very hard to predict.
Flood defenses can protect cities and their inhabitants.
Building codes can ensure flood and windproof buildings.