Sahel

The Sahel is a region in West Africa. 

It is a strip of dry land about 5500 kilometres long and 450 kilometres wide. The Sahel covers parts of (from west to east) the Gambia, Senegal, southern Mauritania, central Mali, Burkina Faso, southern Algeria and Niger, northern Nigeria and Cameroon, central Chad, southern Sudan, and northern South Sudan. It lies at the southern edge of the Sahara Desert and is located between the dry desert land to the north and the forest areas to the south.

Climate
The Sahel has a semi-arid climate. The temperature is high throughout the year. 
There is little rainfall in the Sahel (between 100-150 mm and 600mm). It is concentrated during summer months and can be unreliable. It may be very dry in some years, especially if a large area of low pressure, which brings rain, is not carried North over the Sahel by strong winds.

Desertification
The Sahel is facing a big problem, Desertification. The distribution of rainfall in the Sahel region is uneven. The rainfall in the region has been below average since 1970. The Sahel is becoming drier on the whole. The problem of drought affects most of the countries. As a result, crops and animals die. 

Soil erosion
There is no vegetation to protect the soil, which is then removed by flash floods and strong wind. This leads to soil erosion. 

Deforestation
The population in the Sahel is growing. To meet the ever-increasing demand for firewood, a lot of trees have been cut down. More land has become barren. This is called deforestation. 

Overcultivation
Because people farm intensively in order to grow more crops, the soil becomes dry and infertile. If this process continues for a long time, no crops can be grown. This is called overcultivation. 

Overgrazing
People keep many animals for food. However, the grass cannot support so many grazing animals. This is called overgrazing. 

Deforestation

Deforestation is clearing Earth's forests on a massive scale, often resulting in damage to the quality of the land. The habitats of the animals are lost and many animals die. At the moment every 90 minutes the tropical rainforest in the Amazon will be 2.2 square kilometres smaller. That is about 270 football pitches.

Deforestation also results in global warming (climate change).

Forests still cover about 30 percent of the world’s land area, but areas of the size of Panama (± 75,000 sq. km) are lost each and every year.

The world’s rain forests could completely vanish in a hundred years at the current rate of deforestation.

Forests are cut down for many reasons, but most of them are related to money or to people’s need to provide for their families. The biggest driver of deforestation is agriculture. Farmers cut forests to provide more room for planting crops or grazing livestock. 

Often many small farmers will each clear a few acres to feed their families by cutting down trees and burning them in a process known as “slash and burn” agriculture.

Forests are often planted to protect against natural disasters. When forests are lost, very often the soil they protected is also lost. This loss of soil is often called erosion. We give out carbon dioxide when we breathe and plants and trees take it in by photosynthesis. 

Without forests rain falls scarcely on hot areas.

Erosion

Erosion is the process of natural forces moving rocks and soil. Rocks and soil can be referred to as earth materials.

The natural forces that make erosion happen are:

water	water	Happens when water moves the pieces of rock or soil downhill and carries small pieces of material with it.
	waves	Carry away small pieces of material. A wave can wash up onto the surface of rock or soil and then carry away pieces of material as it flows back into the ocean or lake.
Wind		Occurs when wind moves pieces of earth materials. Wind erosion is one of the weakest kinds of erosion. Small pieces of earth material can be rolled along the ground surface by wind. Very small pieces can be picked up and carried by the wind. Occasionally, wind can carry small pieces of earth materials over large distances.
Ice		Usually happens when a glacier moves downhill. As the ice of the glacier moves downhill, it pushes and pulls earth materials along with it. Ice erosion is one of the strongest kinds of erosion because glaciers can move very large rocks.
Gravity		Is the simplest kind of erosion. Gravity simply pulls loose earth materials downhill. Landslides are dramatic examples of gravity erosion).

Erosion is a geological process. Geology is the study of the structure of the earth and the processes that change the earth. Erosion occurs only at the earth's surface.

Most of the energy that makes erosion happen is provided by the sun. The sun's energy causes the movement of water and ice in the water cycle and the movement of air to create wind. If the sun did not provide energy for erosion, only gravity erosion would still occur.

Erosion can cause problems that affect humans. Erosion can also cause problems for humans by removing rocks or soil that support buildings.

Difference between low, middle and high altitudes

The next graphic shows the difference the low, middle and high altitudes.

Longitude

Longitude is a way to say where a place is on the Earth. 

It is measured starting from an imaginary north-south line called the Prime Meridian. (A meridian is an imaginary line drawn from the North Pole to the South Pole.) Longitude says how far east or west of the Prime Meridian any place is.

Longitude is measured using degrees, the same way an angle is. The Prime Meridian is 0° (zero degrees), and the farthest away is +180° eastward and -180° westward. 

Latitude

Latitude is a measure of the distance you are located from the equator.  

It is commonly shown as an imaginary horizontal line that goes across the earth on maps and is used along with longitude as a reference point to determine location. 

The definition of latitude is the angular distance north or south from the earth’s equator measured through 90 degrees. 

Lines of latitude form circles around the earth, with 0 degrees latitude being at the equator and 90° latitude representing the poles. 

For example:

• Amsterdam, The Netherlands, is located at approximately 52 degrees North latitude, Madrid, Spain, is located at approximately 40 degrees North latitude,
• São Paulo, Brazil, is located at approximately 23 degrees South latitude and
• Cape Town, South Africa, is located at approximately 33 degrees South latitude.

Albedo

The amount of sun's rays that is reflected by an earthly body is called albedo. The word albedo is derived from albus, a Latin word for white.

Albedo is a measure of how much light that hits a surface is reflected without being absorbed.  Something that appears white reflects most of the light that hits it and has a high albedo, while something that looks dark absorbs most of the light that hits it, indicating a low albedo.

It is the reflection of a certain area of earth, like snow and mountains, on the surface. 
For example, the albedo of snow covered mountains hurts the eyes. 

Material	Albedo values (% reflected)
Fresh snow	80% - 95%
Light roof	35% - 50%
Grass	25% - 30%
Bricks and stone	20% - 40%
Concrete dry	17% – 27%
Water bodies	10% - 60%
Forest	10% - 20%
Crops and grassland	10% - 25%
Dark roof	8% - 18%
Asphalt	5% - 10%
Earth’s albedo (average)	31%

The Coriolis effect

The Coriolis effect is a force that is found in a rotating object. Due to earth's rotation, the freely moving things in the Northern Hemisphere move towards the right and in the Southern Hemisphere they move towards the left. This is called the Coriolis Effect. This effect is seen on winds, ocean currents and airplanes.

The next video explaines the Coriolis effect.

The French scientist Gaspard Gustave de Coriolis first described the Coriolis effect in 1835 using mathematics.

The Coriolis effect can best be seen in hurricanes. In the northern hemisphere, or part of the earth, they spin clockwise, in the southern hemisphere they spin the other way. This happens because the earth spins on its tilt.

VIDEO: Coriolis effect

The Clifton Suspension Bridge

The world famous Clifton Suspension Bridge is a suspension bridge, which opened in 1864. Spanning the Avon Gorge and the River Avon. The Clifton Suspension Bridge was designed by the famous Victorian engineer Isambard Kingdom Brunel.

Work actually began in 1831, and by 1843, with only the towers completed, the project was abandoned. 

Brunel died aged only 53 in 1859, but the Clifton Suspension Bridge was completed as his memorial. 

Designed in the early 19th century for light horse drawn traffic, it still meets the demands of 21st century commuter with 11-12,000 vehicles crossing it every day.

Dimensions
Clearance:	75 m above high water level
Dip of chains:	21.34 m
Height of towers:	26 m above deck
Overall length:	412 m
Overall width:	9.45 m
Span:	214.05 m

Aral sea

Images of the Aral sea between Kazakhstan and Uzbekistan, taken in 1973, 1987, 1999, 2004, 2007 and 2009, show how it has virtually disappeared after the rivers that fed it were diverted by irrigation projects. The Aral sea was once one of the largest lakes on earth.

Favelas

A favela is the term for a slum or a shanty town in brazil. They are mostly found on the outskirts of urban areas. Most of the favela is on a very steep hill, with many trees surrounding it. 

The people living in the favelas are the poor, and the rich people live in the city. And the vast majority of the population is black.

Most of the buildings in favelas are made out of cheap materials, like wood, plastic, glass and scrap material. 

The people usually build their houses themselves and invite their friends to help them build. 

The favelas are illegal, because the people do not pay tax. Despite the attempts to cleanse Rio de Janeiro and São Paulo of favelas, the poor population grew at a rapid pace. 

In 1969, there were approximately 300 favelas in Rio de Janeiro; today there are twice as many. In 1950, only 7 percent of Rio de Janeiro's population lived in favelas, nowadays this number has grown to 19 percent or about one in five people living in a favela. 
Census data shows that in 2010, about 6 percent of the population lived in slums in Brazil. 

Crime (and especially the cocaine trade) is common in favelas, as many of the people have no other way to make money. The cocaine trade has affected the favelas. The favelas tend to be ruled by drug lords. Police in Rio de Janeiro are seeking to take back control of many of the cities main favelas from drug gangs before playing host to matches in the 2014 World Cup and the 2016 Olympic Games.

The photo above shows a resident who was shot and lies on the ground as others help him during a police operation at a slum in Rio de Janeiro

Regular shoot-outs between traffickers and police and other criminals, lead to murder rates in excess of 40 per 100,000 inhabitants in the city of Rio and much higher rates in some Rio favelas. 

The favela Rocinha (69,300 - number of inhabitants in 2010, 150,000 – estimated approximate true number of inhabitants of Rocinha) is the largest favela in Rio de Janeiro and in Brazil, and is located in Rio de Janeiro's southern part. Rocinha is built on a steep hillside overlooking Rio de Janeiro, and is located about one kilometre from a nearby beach.  

Las Vegas and the desert water pipeline

The city of Las Vegas wants to pump up to 300 billion litres of water a year out of the Nevada desert and transport it 480 kilometres south to the thirsty city.

In Las Vegas, where the population had been doubling every ten years, planners had an idea. What if there were a way of pumping the water towards Las Vegas? 

Water was ever an issue in the American west. For 100 years, Nevada and other south-western states have shared the waters of the Colorado river (and Lake Mead). 

But Lake Mead begins to decline in the past decade as Las Vegas expands. 

The city, which for years has been drawing more water from its Lake Mead reservoir than has been flowing in, could be at serious risk of going dry in 20 years, said Pat Mulroy, the manager of the Southern Nevada Water Authority. 

The city needed a new plan. When you have got a community of 2 million people and it is 90% reliant on the Colorado river you have to have a contingency plan, she said. The Water Authority has spent 79 million dollars to buy up water rights and they wants to pump up to 300 billion litres of water a year. A study last summer warning the pipeline would lower water tables in some valleys by up to 60 metres over the coming decades. Smaller springs would dry up completely and the animals that depend on them would die off.

Water in the Netherlands

Section 16  - Water in the Netherlands

40% of the Netherlands is below sea level.

The struggle against the sea / water (the fight against).

New landscapes are created.

• terps = protection against the rising sea level.

• dikes = initially only used as protection, later more offensive, to reclaim land. For example salt meadows (= kwelders) outside the dikes were reclaimed.

Polders

Water level is regulated. 

Types of polders:

• - sea polders
• - peat polders
• - “droogmakerijen”

Problem = outside water can seep through the dikes into the polder.

More space for water

In the past = ‘watermanagement’ = to keep the land dry.

In the future = ‘watermanagement‘ = water will be retained, areas will be deliberately flooded.

Why ? Climate change – (1) summers drier, winters wetter. (2) sea level is rising.

Space for rivers

• to keep the land dry water was discharged by (1) digging ditches and canals or (2) strainghtening out streams (3) pumping stations.
• in the future water will even be retained, certain areas will be deliberately flooded.

A permanent coast

• dikes must be reinforced due to the rising sea level.
• sand replenishment = due to erosion.

Dehydration

• dehydration (verdroging) drop in the ground water level.
• extinction of certain vegetation = drought.
• water table has dropped by 30 cm. 

Why?

1. farming (water extraction for irrigation)
2. drinking water (water extraction)
3. industry (water extraction)
4. asphalting = less water can subside into the underground (deceased infiltration / seep through) 

Managing and Reducing Losses from Water