Rainfall occurs when water vapor in the atmosphere condenses into droplets. The water cycle describes the process by which water evaporates from bodies of water, rises into the sky as vapor to form clouds, condenses into rain or other precipitation and falls back to earth. Rain is measured using rain gauges, which collect rainfall and some record amounts electronically or on charts driven by clockwork mechanisms. The document discusses different rain intensities, types of rainfall formation, and factors that influence rainfall amounts.

3. DEFINITION OF
RAINFALL

4. Rainfall is a form of Precipitation.
It occurs when water vapor in the
atmosphere condenses into droplets that can
no longer be suspended in the air.

5. FORMATION OF
RAIN

6.  It is called as Water Cycle or Hydrological Cycle.
 The process of Hydrological Cycle are as follows –
1. Water in the water bodies evaporate due to the
heat energy provided by Solar Radiation.

7.  It is called as Water Cycle or Hydrological Cycle.
 The process of Hydrological Cycle are as follows –
1. Water in the water bodies evaporate due to the
heat energy provided by Solar Radiation.
2. The water vapor moves upwards and forms
clouds.

8.  It is called as Water Cycle or Hydrological Cycle.
 The process of Hydrological Cycle are as follows –
1. Water in the water bodies evaporate due to the
heat energy provided by Solar Radiation.
2. The water vapor moves upwards and forms
clouds.
3. While much of the clouds condense and fall
back to the oceans as rain, a part of the clouds
is driven to the land areas by winds.

9.  It is called as Water Cycle or Hydrological Cycle.
 The process of Hydrological Cycle are as follows –
1. Water in the water bodies evaporate due to the
heat energy provided by Solar Radiation.
2. The water vapor moves upwards and forms
clouds.
3. While much of the clouds condense and fall
back to the oceans as rain, a part of the clouds
is driven to the land areas by winds.
4. There they condense and precipitate onto the
land mass as rain, snow, hail, drizzle, etc.

11. SIZE & INTENSITY

12. Size of Rainfall
Minimum size of Raindrop is 0.5 mm.
Maximum size of Raindrop is about 6 mm.
Intensity of Rainfall
TYPE INTENSITY
Light Rain up to 2.5 mm/hr
Moderate Rain 2.5 mm/hr to 7.5 mm/hr
Heavy Rain > 7.5 mm/hr
Violent Rain > 50 mm/hr

13. TYPES OF
RAINFALL

14. Following three are the types of rainfall –
1. Convective Rainfall
2. Orographic Rainfall
3. Frontal or Cyclone Rainfall

15.  A packet of air which is
warmer than the
surrounding air due to
localized heating rises
upward and
consequently undergo
cooling, condensation
and precipitation.

16.  The moist air masses
get lifted up to
higher altitudes due
to the presence of
the mountain barriers
and consequently
undergo cooling,
condensation and
precipitation.

17.  When two air
masses meet, they
do not mix readily
due to differences
in temperature and
density. A front is
an imaginary line
separating two
contrasting air
masses.

18. MEASUREMENT OF
RAINFALL

19.  The rainfall is collected and measured in a raingauge.
 Terms such as pluviometer, ombrometer and hyetometer are also
sometimes used to designate a raingauge.
 For sitting a raingauge the following consideration are important:-
1. The ground must be level and in the open and the instrument
must present a horizontal catch surface.
2. The gauge must be set as near the ground as possible to reduce
wind effects but it must be sufficiently high to prevent flooding,
etc.
3. The instrument must be surrounded by an open fenced area of at
least 5.5 m X 5.5 m.
4. No object should be nearer to the instrument than 30 m or twice
the height of the obstruction.

20. Raingauge can be broadly classified into two categories –
NON RECORDING GAUGES-
o Symon’s Gauge
RECORDING GAUGES-
o Tipping Bucket Type
o Weighing Bucket Type
o Natural Syphon Type

21. NON RECORDING GAUGE
(SYMON’S GAUGE)
 It is extensively used in India.
 Water contained in the
receiving vessel is measured
by a suitably graduated
measuring glass with an
accuracy up to 0.1 mm
 The rainfall is measured
everyday at 8:30 AM(IST) and
is recorded as the rainfall of
that day.
 The receiving bottle normally
does not hold more than 10 cm
of rain.

22. RECORDING GAUGE
(Tipping Bucket Type)
 The catch from the funnel
falls onto one of a pair of
small buckets.
 When 0.25 mm of rainfall
collects in one bucket, it tips
and bring the other one in
position.
 The tipping actuates an
electrically driven pen to trace
a record on clockwork driven
chart.

23. RECORDING GAUGE
(Tipping Bucket Type)
 The water collected on
the bucket exit from
drain hole.
 Then the water collected
in a storage can.

24. RECORDING GAUGE
(Weighing Bucket Type)
 The catch from the
funnel empties into a
bucket mounted on a
weighing scale.
 Its contents recorded on
a Clockwork driven
chart.
 The clockwork
mechanism has the
capacity to run for as
long as one week.

25. RECORDING GAUGE
(Natural Syphon Type)
 The rainfall collected
causing the float to rise.
 A pen attached to the
float records the
elevation on a rotating
drum driven by a
Clockwork mechanism.
 A syphon empties the
chamber by a syphonic
action.
 It is adopted as the
standard recording type
rain gauge in India.

26. FACTORS AFFECTING
THE AMOUNT OF
RAINFALL

27. Factors which affect the amount of rainfall are –
• Latitude
• Temperature
• Moisture
• Air Masses
• Frontal Activity
• Differential Heating
• Mountain Barriers
• Distribution of Land & Water