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1

EARTH’S ATMOSPHERE

The atmosphere is a thin Gaseous-Layer, Air, which surrounds or envelops the earth, extending

up to 1,600 km above the surface.

Weather and climatic patterns are the results of changes and variations in the behaviour of the

atmosphere. The different kinds of atmospheric behaviour produce different weather at different

times.

CLIMATE & WEATHER

Weather and climate are not exactly the same, though they both describe atmospheric conditions.

Weather is the short term, normal day-to-day, atmospheric conditions which prevail at a given

place at a given time. The weather can be described as; stormy, rainy, hot, windy, humid, and

sunny.

Climate on the other hand is the "average weather" of an area over a much longer time span.

Often, hundreds or thousands of years

CLIMATE CHANGE

Climate change is a significant and lasting change in the statistical distribution of weather

patterns over periods ranging from decades to millions of years. It may be a change in average

weather conditions, or in the distribution of weather around the average conditions

Climate Change is a shift in long-term weather patterns:

Temperature, Precipitation (rain/snowfall etc), Wind and more

There is scientific consensus that it is largely as a result of human activities. These human

activities include the combustion of fossil fuels, which increases atmospheric concentrations of:

Carbon dioxide (CO2)

Methane (CH4)

Nitrous oxide (N2O)

Other heat-trapping (green house) gases

These greenhouse gases form a blanket of pollution that traps heat in the atmosphere and causes

climate instability characterized by severe weather events.

SEVERE WEATHER EVENTS Storms,

Droughts,

Floods,

Heat Waves and

Rising Sea Levels

EVIDENCE OF PAST CLIMATE

The four main types of evidence indicating climatic conditions that existed in the past are;

Geological

Geomorphological

Chemical

Paleontological

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2

Geological

Observations of aerial photographs of desert areas reveal that the desert areas were once

occupied by vegetation.

Geomorphological Geomorphology is the study of the earth’s surface and the changes that occur there.

e.g. River deltas

Chemical Variations in the ratios of isotopes in fossils present in sediments and sedimentary rocks and

ocean sediment cores

Paleontological Changes in the geographical distribution of fossils

Palaeontology is the study of prehistoric plants and animals based on fossils.

Fossil is a relic or trace of living thing preserved in rocks

Past Climates (e.g. Ice Age)

Ice Age - time in recent geologic past when extensive continental glaciers covered larger areas

than they do now.

Ice Age and their possible causes

Ice age may be caused by;

Fluctuations in the amount of incoming solar radiation, OR

Blocking of incoming solar radiation by particles such as volcanic dust or sulphuric-acid droplet

in the atmosphere

Once these phenomena happen, the earth cannot trap enough heat to warm its atmosphere. This

can result in the cooling which can induce the start of an ice age.

THE SUN/RADIATION

The main and chief source of energy to the earth is the sun. The sun’s energy travels through the

earth’s atmosphere to reach the earth’s surface in the form of electromagnetic radiations (rays of

light, heat, and charged particles etc.)

These radiations are made up of x-rays, Ultraviolet (UV), Visible light, Infrared (IR),

Microwave, Radio and TV broadcast wave and other forms of energy.

Of major concern are

Ultraviolet (UV) rays

Infrared (IR) rays

GREENHOUSE EFFECT & GLOBAL WARMING

The temperature of the earth depends on the amount of energy we receive from the sun and the

amount of energy lost back out to space.

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3

The atmosphere influences the temperature at earth's surface. (Average temperature is 140C).

Sunlight

When the sun’s rays are incident towards the earth, the incoming sunlight (UV, IR, etc.) heats the

earth directly. A significant portion of the UV which is very harmful to humans and other forms

of life is absorbed in the atmosphere by some of the gases and the ozone layer before it reaches

the earth. The ozone layer is a layer in Earth's atmosphere that absorbs most of the Sun's UV

radiation. It contains relatively high concentrations of ozone (O3), although it is still very small

with regard to ordinary oxygen, and is less than ten parts per million, the average ozone

concentration in Earth's atmosphere being only about 0.6 parts per million. The ozone layer is

mainly found in the lower portion of the stratosphere from approximately 20 to 30 kilometres (12

to 19 mi) above Earth, though the thickness varies seasonally and geographically.

Infrared (IR)

In turn heat (IR) rays, radiating outward from the earth’s surface heats the atmosphere.

Thus, the earth surface absorbs the solar radiation and releases it back to the atmosphere as

infrared radiation, some of which goes back into space.

This process helps to keep the temperature of the earth at a level conducive to life.

The problem however has to do with the increase in the concentration of greenhouse gases such,

Nitrous oxide,

Methane (CH4)

Chlorofluorocarbons (CFCs),

Carbon dioxide (CO2) and

Ozone in the atmosphere

Some of the infrared radiation emitted by the earth is absorbed by these gases in the atmosphere

that subsequently re-emit the energy as heat back towards the earth’s surface

Trapping of infrared radiation in the atmosphere is known as enhanced greenhouse effect and it

increases the average temperature of the earth.

Thus, the more greenhouse gases we have in the atmosphere, the likelihood is that global

warming will increase

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4

CONTRIBUTION OF HUMANS TO THE GREENHOUSE EFFECT

The burning of natural gas, coal and oil, including gasoline for automobile engines, raises

the level of carbon dioxide in the atmosphere and hence leads to global warming.

Long-lasting industrial gases that do not occur naturally are produce by factories,

contribute significantly to the enhanced greenhouse effect and global warming.

Deforestation also contributes to global warming. Trees use carbon dioxide and give off

oxygen in its place, which helps to create the optimal balance of gases in the atmosphere.

Some farming practices and land-use changes increase the levels of methane and nitrous

oxide

Population growth is another factor in global warming, because as more people use fossil

fuels for heat, transportation and manufacturing the level of greenhouse gases continues

to increase.

As more farming occurs to feed millions of new people, more greenhouse gases enter the

atmosphere.

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5

EFFECTS OF GLOBAL WARMING

Sea Level Rise – increase in temperatures may cause ice (especially at the polar regions)

to melt into water which then flows into the oceans and seas, increasing water level.

Extinction: Rising temperatures would change the habitats of endangered species,

leading to their extinction.

Spread of Disease Certain vector-borne diseases carried by animals or insects, such as malaria, would

become more widespread as warmer conditions expand their range.

MEASURES ADOPTED TO REDUCE GLOBAL WARMING

Cutting down on use of fossil fuels (e.g., coal, petroleum and natural gas),

Increasing the use of renewable energy (e.g., solar, wind, and geothermal heat),

Expanding forests,

Making lifestyle choices that help to sustain the environment

FLOODS

Heat trapped in the atmosphere can causes climate instability characterized by severe weather

events such as flooding. Floods are probably the most widely experienced catastrophic

geological hazards. Some floods may be the result of unusual events such as collapse of a dam.

The vast majority of floods are however normal, and predictable. A part of the functioning of the

Hydrological Cycle

FLOODS IN GHANA

In Ghana, Floods are classified as:

Rainfall-Runoff Flooding

River Flooding

Lagoon Flooding

Tidal flooding

Man-made flooding ( blocking of river courses etc)

EARTH’S HYDROSPHERE A hydrosphere is the total amount of water on a planet. The hydrosphere includes water that is on

the surface of the planet, underground, and in the air. A planet's hydrosphere can be liquid,

vapor, or ice.

All bodies of water and ice, as well as water vapour in the atmosphere make up the earth’s

hydrosphere.

Oceans blanket nearly 71 percent of Earth’s surface and account for more than 97 percent of

Earth’s water.

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6

The hydrosphere also includes the fresh water found:

Underground

In Streams,

Lakes,

Glaciers

Composition of the hydrosphere Oceans ……… ` 97.2%

Glaciers ……… 2.15%

Groundwater ………. 0.62%

Freshwater Lakes ……… 0.009%

Saline Lakes and Inland seas ………. 0.008%

Stream Channels ……….. 0.001%

Water Vapour in the Atmosphere ……… 0.001%

THE HYDROLOGIC CYCLE

All the water in the hydrosphere is caught up in the Hydrologic Cycle.

The water cycle, also known as the hydrologic cycle or the H2O cycle, describes the continuous

movement of water on, above and below the surface of the Earth. The mass water on Earth

remains fairly constant over time but the partitioning of the water into the major reservoirs of ice,

fresh water, saline water and atmospheric water is variable depending on a wide range of

climatic variables. The water moves from one reservoir to another, such as from river to ocean,

or from the ocean to the atmosphere, by the physical processes of evaporation, condensation,

precipitation, infiltration, runoff, and subsurface flow. In so doing, the water goes through

different phases: liquid, solid (ice), and gas (vapor).

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7

Floods – The Hydrologic Cycle

The hydrologic cycle begins with precipitation in the form of snow or rain, representing the

initial input into the hydrologic system.

The main processes of the hydrologic cycle are:

Evapotranspiration

Surface Runoff

Infiltration

Streams Systems

Oceans

EVAPOTRANSPIRATION

Evapotranspiration is the sum of evaporation and plant transpiration from the Earth's land surface

to atmosphere.

A fraction of the precipitation is returned to the atmosphere by two processes;

Evaporation and Plant Transpiration Evaporation, driven by solar energy, is the physical conversion of some of the precipitation to

water vapour that is returned to the local atmosphere.

Plant Transpiration - the process by which plants lose water in the form of vapour through their

stomata in leaves into the atmosphere

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8

SURFACE RUNOFF

Surface runoff is water, from rain, snowmelt, or other sources, that flows over the land surface,

and is a major component of the water cycle.

The runoff tends to move toward sinks or storage locations such as;

Streams/rivers

Lakes

Wetlands

The Oceans

The runoff fraction is a major factor leading to river flooding.

INFILTRATION

Infiltration is the process by which water on the ground surface enters the soil

A fraction of the precipitation moves down into the ground, and infiltrate into the subsurface.

Unsaturated Zone: the upper part of the ground in which the pore spaces of the rock/soil is

partially filled with air and partly with water.

Saturated Zone: this is the zone between the base of the unsaturated zone and an impermeable

rock below, within which water accumulates.

STREAMS SYSTEMS AND THEIR FEATURES

A stream is body of flowing water confined within a channel, regardless of size. It flows

downhill through local topographic lows, carrying water away over the earth’s surface

In addition to that, the size of a stream is influenced by the following factors;

Climate, including the amount of precipitation and evaporation

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Vegetation or lack of it

The underlying geology

CONSEQUENCE AND DEVELOPMENT OF FLOODPLAINS

Large volumes of water flowing in streams often leads to flooding

The over flow of a streams banks due to higher discharge is termed flood.

Flood occurs when a stream runs out of its confines and submerges surrounding areas.

A majority of stream floods are linked to precipitation. However, when rainfalls or snow melts,

some of the water infiltrates, or sinks into the ground. It may then percolate through soil and rock

at greater depths.

FACTORS AFFECTING FLOODING

Dam & Levee Failures

The Role of Precipitation

Porosity and permeability of the underlying rock

Topography

Vegetation

FLOOD CHARACTERISTICS

The elevation of the water at any point is termed the stage of the stream.

A stream is at flood stage when the stream stage exceeds bank height.

Upstream floods are floods that affect only small localized areas (streams draining small basins).

They are caused by sudden, locally intense rainstorms and by events like dam failure.

Downstream floods are floods that affect large stream systems and large drainage basins. They

result from prolonged heavy rains over a broad area or from extensive regional snowmelt.

EFFECTS OF DEVELOPMENT ON FLOOD HAZARDS

Floods are normally caused by one or a combination of the following activities and

processes.

Materials used to cover the ground when cities are built, such as roads asphalt and

concrete, are relatively impermeable and greatly reduce infiltration.

Buildings in a floodplain also can increase flood heights. The buildings block the original

river channel and occupy volume that water formally could fill, and a give discharge

corresponding to a higher water level

Both farming and urbanization also disturb the land, by removing natural vegetation, and

thus, exposing the soil to erosion

Indiscriminate dumping of garbage and other solid materials into drains is common, thus

impeding the flow of water.

It is also common to observe drains that have experienced siltation, where silt- and sand-

sized particles settle in the drains, and subsequently reducing its volume.

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10

HAZARDS ASSOCIATED WITH FLOODS

Primary effects include injury, loss of life, and damage caused by swift currents, debris, and

sediment to farms, homes, building, railroads, roads, bridges and urban communication and

supply systems.

Secondary effects may include short-term pollution of rivers, hunger and disease, and

displacement of persons who have lost their homes.

In addition, fires may be caused by cuts in electrical circuits or gas mains broken by flooding and

associated erosion.

STRATEGIES FOR REDUCING FLOOD HAZARDS

Restrictive Zoning and ‘’Floodproofing’’ – this involves identifying an area threatened by

floods of different recurrence intervals. Once this is done, the land might best be restricted to

land uses not involving much building.

Retention Ponds and Diversion Channels - ponds are large basins that trap some of the surface

runoff, keeping it from flowing immediately into the stream. Diversion channels come into play

as the water level in streams rises.

The channels are used to redirect some of the water flow into areas adjacent to the stream where

flooding will cause minimal damage.

Channelization – This refers to the modification of a stream channel itself intended to increase

the velocity of water or volume of the channel, or both.

Levees – These are raised banks along a stream channel.

Flood-Control Dams and Reservoirs

Removal of waterweeds, garbage and other obstacles that block the drains and prevent free flow

of water

CLIMATE-RELATED HAZARDS IN GHANA

Wind/Rain storm: Country wide especially rural areas

Other Climate-Related hazards in Ghana

Flooding:

Low lying areas in towns and cities - e.g. Accra, Kumasi,

Along major rivers and the Volta lake - eg. Northern Ghana, Western Region, Eastern

Region etc.

Tidal Waves and Sea Level rise: (Keta, Ada, Busua)

Bush/Wild Fires: Northern sector and transitional zone- Brong Ahafo, Northern volta and

Afram Plains

Desertification: Northern Regions

Drought/famine: Northern sector and transitional zone

Extreme temperatures: Northern regions