CC 606 : HYDROLOGY
Chapter 2 :Type Of Rainfall
REG NO :
NORFARHANA AIN BINTI ZAINAL ARIFF
ZURHAYATI BINTI MAT ESA
NURUL HUSNA BINTI MOHAMED ROSHIDI
SOLEHUDDIN BIN JAMAL ABD NASER
NORSYAMIMI BINTI KHOSIDI
SITI RASHIDAH BINTI ABD RAZI
• Artificial rainfall is also known as Cloud Seeding.
• Cloud seeding is a weather modification system that aims
to boost precipitation or rain by introducing condensation
nuclei such as salt or dry ice
The first stage is Agitation. That is using chemicals to
stimulate the air mass upwind of the target area to rise and
form rainclouds. The chemicals used during this stage are
calcium chloride, calcium carbide, calcium oxide, a
compound of salt and urea, or a compound of urea and
ammonium nitrate. These compounds are capable
of absorbing water vapor from the air mass , thus
stimulating the condensation process
The second stage is called Building-up stage. Here the
cloud mass is built up using chemicals such as kitchen
salt, the T.1 formula, urea, ammonium nitrate, dry ice,
and occasionally also calcium chloride to increase nuclei
which also increase the density of the clouds
In the third stage of bombardment chemicals such as super-cool
silver iodide and dry ice are used to reach the most unbalanced status
which builds up large beads of water (Nuclei) and makes them fall
down as raindrops. The process is called seeding
The Chemicals used in the production of artificial rain could affect
climatic patterns, ecosystem, water sources and the soil.
Once started this process is uncontrollable.
Cloud Seeding causes Flood's, Hurricane's and Thunderstorm's which
result's in loss of many lives.
• Convection occurs when the Earth's surface,
mainly in the equatorial region, within a
conditionally unstable, or moist atmosphere,
becomes heated more than its surroundings,
leading to significant evaporation.
• It falls as showers with rapidly changing intensity.
• Convective precipitation falls over a certain area
for a relatively short time, as convective clouds
have limited horizontal extent.
• The word "orographic" means that it is related to mountains.
• Orographic rainfall is when a parcel of air containing water
vapor gets to a mountain ,it is then forced upwards (the
mountain blocking its way ).
As the parcel of air is forced upwards, it expends (adiabatic
expansion ) and also cools. As it cools ,it becomes saturated
because the amount of water it can hold decreases ,so the
water vapor begins to condense and finally falls as rain.
At mountainous regions, air drops down over the
high ground, gaining temperature and increasing the
amount of water it can hold.
That is why the flat regions below mountains hardly
experience rain, and this area is known as rain
What is Frontal Rainfall?
Frontal rainfall can be defined as the rising of a warm air mass over a
cool air mass. This is then followed by condensations and felling of rainfall.
Frontal rain is rain that occurs as a result of meeting the hot air mass and
cold air mass.
Frontal Rainfall occurs when
Two air masses meet, one a warm air mass and one a cold air mass.
The lighter, less dense, warm air is forced to rise over the denser, cold
This causes the warm air to cool and begin to condense.
As the warm air is forced to rise further condensation occurs and rain is
Frontal rain produces a variety of clouds, which bring moderate to
An area of warm air meets and area of cold air.
The warm air is forced over the cold air
Where the air meets the warm air is cooled and
water vapour condenses.
Clouds form and precipitation occurs
What is Cyclonic Rainfall???
Cyclonic or 'frontal' rain occurs where two
air masses meet and form a 'front'. The
warmer, moisture laden air rises over the
colder air as a 'warm front'. As the air rises
it cools, and its relative humidity
increases. Clouds form as water vapour
condenses, and then fall as rain
Where does frontal/cyclonic rain fall occur?
"Frontal/Cyclonic rain is caused by cyclonic activity and
occurs along fronts.
It is formed when two air masses of different
temperature, humidity and density meet such as the
meeting of a tropical maritime air mass and a polar air
A zone called a front separates them. At the warm
front, the lighter warm air rises gently over the heavier
cold air which remains close to the ground.
As the warm air rises, it expands and cools and
condenses to form clouds (altostratus). The rain falls
steadily for a few hours to several days.
At the cold front, the cold air forces warm air up
aggressively, causing it to rise quickly and condense,
forming cumulonimbus clouds.
The heavy rain that falls is of short duration. Such
rain is usually associated with temperate depressions
Cyclones form in which month?
from May till June and then from
September till October
15 April to 15 Julyand also after its
withdrawal that is 15 September to 15
DESTRUCTIVE ELEMENTS IN TROPICAL CYCLONES
Cyclone producing heavy rainfall and
A mosque is submerged after Cyclone
Yemyin made landfall in Balochistan
Fully formed tropical cyclone with an eye, eyewall, and
circulating rain bands