METEOROLOGICAL DISASTERS,
PREPAREDNESS, MONITORING,
With Special Reference to
DROUGHTS
Y.K. REDDY
Director
Meteorological Centre,
HYDERABAD
1
INTRODUCTION
•A Disaster is a serious disruption of the functioning of a society,
causing widespread human, property or environmental losses
which exceed the ability of the affected society to cope using only
its own resources.
•Natural Disasters that commonly affect Indian Areas are:
•TROPICAL CYCLONES; - affect Agriculture Sector
•EARTH QUAKES;
•TSUNAMIS;
- affect Agriculture Sector
•FLOODS;
- affect Agriculture Sector
•DROUGHTS;
- affect Agriculture Sector
2
TROPICAL CYCLONES
Favourable conditions for a Cyclonic Storm
 Pre existing area of disturbed weather
 Sea surface temperatures greater than 80˚ Fahrenheit/26.5 ˚
Centigrade
 Warm ocean water must be at least 200 feet deep (waves can’t bring
up cold water)
 Absence of wind shear
 Not closer than 5˚ latitude from Equator
CYCLONE SEASONS
(For Indian Seas)
Pre-Monsoon Cyclone Season : March to May
Post Monsoon Cyclone Season : October to December
3
Dimentions of Tropical Cyclones
Size
Speed of Movement
Large (700-1000km dia)
10-14 kmph (Slow)
Medium (300-700km dia)
15-25 kmph (Moderate)
Small (<300km dia)
>25 kmph (Fast)
4
MONITORING OF CYCLONES BY IMD
•One of the most important functions of IMD
•A constant watch is kept on the Arabian Sea and the Bay of Bengal
for the likely genesis of tropical cyclones with the help of satellite
imagery.
•Data from ships and ocean buoys is also very valuable.
• When the systems come nearer to the Indian coastline, their
subsequent development and movement is monitored by a chain of
Cyclone Detection Radars.
•The likely movement of the storms is predicted with the help of
track prediction models(Computer Programs) and by reference to
past climatology which has been built up using 125 years of cyclone
data.
5
Potential Impact upon Landfall of a Tropical Cyclone
Flooding of LowLying Coastal Areas
Effect of local Tides
Erosion of Beaches
Effect of local Coastal
Configuration
Damage to onshore
& offshore
installations
Damage to Shipping
& Fishing Facilities
Low Atmospheric
Pressure in the Centre
Storm Surge
Loss of Soil
Fertility
from Saline
Intrusion
Land
Subsidence
Contaminatio
n of Domestic
Water Supply
Urban Bushfire
Loss of
Human Life:
Injuries
Wind
Destruction
of
Vegetation,
Crops,
Livestock
Damage to
structures &
Continent
Loss of
Communications
& Power
Rain
Flooding
6
A Storm Surge is an abnormal
rise of sea level caused by a
cyclone moving over a
continental shelf
7
Wind Distribution
in a Cyclone
Band of Maximum winds would be 20 – 50 Km from the Center.
(Variablility: 10 – 150 Km)
In this belt, Speed decreases rapidly towards eye.
But decreases slowly and in an irregular fashion outward from
eye.
The highest wind will be in the northeast sector.
8
Rainfall Distribution
in a Tropical Cyclone
Extensive Rainfall
In the Right forward sector in Recurving to East/NE
In the left forward sector in westerly moving
In the forward sector in north moving
Intensive Rainfall
Occurs to the left of the cyclone
Slow moving/Big size cyclones give more rainfall whereas fast moving/small size ones give
less rainfall
Intensity and Area of Rainfall depends on:
Intensity and size of Storm
Speed of the storm
Orography of Land/Orientation of Coast
Direction of movement of Storm
Rate of ascent of air in the storm circulation
Temperature & Lapse Rate in the System
Continuous moisture feed even over the land into the system
RESULT : FLASH FOODS IN LOW LYING AREAS, BREACHES OF RIVERS,
INUNDATION OF VILLAGES, STANDING CROPS ETC.
9
Impact of Cyclonic Storms and Suggested
Mitigation Actions
Category /
T.No. / Wind
Speed
Structures
Communi
cation &
power
Road/Rail
Agriculture
Marine
Interests
Coastal Zone
Overall
Damage
Category
Suggested
Actions
Deep
Depression
T2.0
28-33 Knots
52-61 Kmph
Minor
damage to
loose/
unsecured
structures
Minor
Some
breaches in
Kutcha
road due to
flooding
Minor
damage to
Banana
trees and
near coastal
agriculture
due to salt
spray.
Damage to
ripe paddy
crops
Very
rough
seas. Sea
waves
about 4-6
m high.
Minor damage
to Kutcha
embankments
Minor
Fishermen
advised not
to venture
into sea.
Cyclonic
Storm
T2.5-T3.0
34-47 Knots
62-87 Kmph
Damage to
thatched
huts.
Minor
damage to
power
and
communi
cation
lines due
to
breaking
of tree
branches.
Major
damage to
Kutcha and
minor
damage to
Pucca
roads.
Some
damage to
paddy
crops,
Banana,
Papaya trees
and
orchards.
High to
very high
sea waves
about 6-9
m high.
Sea water
inundation in
low lying areas
after erosion of
Kutcha
embankments
Minor to
Moderate
Fishermen
advised not
to venture
into sea.
10
Impact of Cyclonic Storms and Suggested
Mitigation Actions
Category /
T.No. / Wind
Speed
Structures
Communi
cation &
power
Road/Rail
Agriculture
Marine
Interests
Coastal Zone
Overall
Damage
Category
Suggested
Actions
Severe
Cyclonic
Storm
T3.5
48-63 Knots
88-117 Kmph
Major
damage to
thatched
houses /
huts.
Roof tops
may blow
off.
Unattache
d metal
sheets
may fly.
Minor
damage to
power
and
communi
cation
lines.
Major
damage to
Kutcha and
some
damage to
Pucca
roads.
Flooding of
escape
routes.
Breaking of
tree
branches,
uprooting of
large
avenue
trees.
Moderate
damage to
Banana and
Papaya
trees. Large
dead limbs
blown from
trees.
Phenomen
al seas
with wave
height 914 m.
Movement
in motor
boats
unsafe.
Major damage
to coastal
crops. Storm
surge upto
1.5m (area
specific)
causing
damage to
embankments/
salt pans.
Inundation
upto 5 Km in
specific areas.
Moderate
Fishermen
advised not
to venture
into sea.
Coastal
hutment
dwellers
advised to
move to
safer
places.
Other
people in
the affected
areas to
remain
indoors.
11
Impact of Cyclonic Storms and Suggested
Mitigation Actions
Category /
T.No. / Wind
Speed
Structures
Communi
cation &
power
Road/Rail
Agriculture
Marine
Interests
Coastal Zone
Overall
Damage
Category
Suggested
Actions
(a) Very
Severe
Cyclonic
Storm
T4.0-T4.5
64-90 Knots
118-167 Kmph
Total
destructio
n of
thatched
houses/
extensive
damage to
Kutcha
houses.
Some
damage to
Pucca
houses.
Potential
threat
from
flying
objects.
Bending/
uprooting
of power
and
communi
cation
poles.
Major
damage to
Kutcha and
Pucca
roads.
Flooding of
escape
routes.
Minor
disruption
of
railways,
overhead
power lines
and
signaling
systems.
Widespread
damage to
standing
crops
plantations,
orchards,
falling of
green
coconuts
and tearing
of palm
fronds
Blowing
down bushy
trees like
mango.
Phenomen
al seas
with wave
heights
more than
14m.
Visibility
severely
affected.
Movement
in motor
boats and
small
ships
unsafe.
Storm surge up
to 2 m,
Inundation up
to 10 Km in
specific areas.
Small boats,
country crafts
may get
detached from
moorings.
Large
Fishermen
not to
venture
into sea.
Evacuation
from
coastal
areas needs
to be
mobilized.
People
advised to
remain
indoors.
Judicious
regulation
of rail and
road traffic
needed.
12
Impact of Cyclonic Storms and Suggested
Mitigation Actions
Category /
T.No. / Wind
Speed
Structures
Communi
cation &
power
Road/Rail
Agriculture
Marine
Interests
Coastal Zone
Overall
Damage
Category
Suggested
Actions
(b) Very
Severe
Cyclonic
Storm
T5.0-T6.0
91-119 Knots
168-221 Kmph
Extensive
damage to
all types
Kutcha
houses,
some
damage to
old badly
managed
Pucca
structures.
Potential
threat
from
flying
objects.
Extensive
uprooting
of power
and
communi
cation
poles.
Disruption
of rail /
road link at
several
places.
Extensive
damage to
standing
crops
plantations,
orchards.
Blowing
down of
Palm and
Coconut
trees.
Uprooting
of large
bushy trees.
Phenomen
al seas
with wave
heights
more than
14m.
Movement
in motor
boats and
small
ships not
advisable.
Storm surge up
to 2 – 5 m,
Inundation may
extend up to
10-15 Km over
specific areas.
Large boats
and ships may
get torn from
their moorings,
country crafts
may get
detached from
moorings.
Extensive
Fishermen
not to
venture
into sea.
Evacuation
from
coastal
areas
essential.
Diversion /
suspension
of rail
traffic may
be
required.
13
Impact of Cyclonic Storms and Suggested
Mitigation Actions
Category /
T.No. /
Wind
Speed
Structures
Communic
ation &
power
Road/Rail
Agriculture
Marine
Interests
Coastal
Zone
Overall
Damage
Category
Suggested
Actions
Super
Cyclonic
Storm
T6.5 and
above 120
Knots and
above 222
Kmph
Extensive
damage to
non
concrete
residential
and
industrial
building.
Structural
damage to
concrete
structures.
Air full of
large
projectiles.
Uprooting
of power
and
communica
tion poles.
Total
disruption
of
communica
tion and
power
supply.
Extensive
damage to
Kutcha roads
and some
damage to
poorly repaired
pucca roads.
Large scale
submerging of
coastal roads
due to flooding
and sea water
inundation.
Total
disruption of
railway and
road traffic due
to major
damages to
bridges, signals
and railway
tracks.
Washing away
of rail / road
links at several
places.
Total
destruction
of standing
crops /
orchards,
uprooting
of large
trees and
blowing
away of
palm and
coconut
crowns,
stripping of
tree barks.
Phenom
enal
seas
with
wave
heights
more
than
14m. All
shipping
activity
unsafe.
Extensive
damage to
port
installations.
Storm surge
more than
5m,
Inundation
up to 40 Km
in specific
areas and
extensive
beach
erosion. All
ships torn
from their
moorings.
Flooding of
escape
routes.
Catastrophic
Fishermen
not to venture
into sea.
Large scale
evacuations
needed. Total
stoppage of
rail and road
traffic needed
in vulnerable
areas.
14
TROPICAL CYCLONE FORECASTING
Of Movement : Various Techniques are available for Track
Prediction of the storm.
i)*
Methods based on climatology
ii)*
Methods based on Persistence & Climatology
iii)*
Synoptic Techniques – Empirical Techniques
iv) *
Satellite Techniques
v)*
Statistical Techniques using climatology,
persistance and Synoptic
vi)*
Analogue Techniques and
vii)
Dynamical Techniques
* Used in Operational Mode.
Of Intensity and Associated Weather:
No reliable
objective techniques. Subjective techniques like Climatology,
Synoptic and Satellite are used. Good Techniques are
available for Storm Surge predictions. But accuracy depends
on the accuracy of input data.
15
CYCLONE
WARNINGS & BULLETINS
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
Four Stage Cyclone Warnings
Fisheries warnings
Weather and Sea bulletins
Port Warnings (Storm Warning Signals)
Coastal bulletins (upto 75 Kms from the coast line)
Aviation Warnings
Bulletins for Indian Navy “Fleet Forecast”.
Bulletins for Departmental Exchange.
Bulletins for AIR/DD
Bulletins for Press
Album page Warnings- to important govt/pvt agencies
16
CYCLONE WARNING
FOUR STAGES:
•I Stage -PRE-CYCLONE WATCH: 72 Hrs in Advance
•Early warning about development of a cyclone, its likely intensification, coastal
belt likely to be affected etc.
•Issued by DGM himself and addressed to Cabinet Secy of GOI and Chief Secy
of concerned State Govts
•II Stage – Cyclone Alert :
•At least 48 Hours in advance of adverse weather by concerned ACWCs/CWCs
•Contains location of storm, direction of movement, intensifi-cation, coastal districts
likely to be affected, adv to fishermen
17
CYCLONE WARNING Cont’d
•III Stage – Cyclone Warning :
•At least 24 hrs in advance by ACWCs/CWCs at 3 hrly
•Contains latest position of cyclone, its intensity, maximum sustained surface wind speed,
forecast of landfall point, time of landfall , impact of strong winds, heavy rain and advice to
fishermen and general public.
•IV Stage – Post Landfall Outlook:
•Issued 12 hrs in advance of expected time of land fall
•Issued by concerned ACWC
•Contains likely direction of movement after landfall, adverse weather likely to be
experienced in the areas away from coast
18
PORT WARNINGS
 IMD maintains a port warnings service by which the Port
officers are
warned about disturbed weather likely to
affect their Ports.
 On receipt of warnings, Port officials hoist appropriate
visual signals so
that they are visible from a distance.
 Ports are warned 5 to 6 times a day during period of
cyclonic storm.
 Warning contains information about location, intensity,
expected
direction, expected land fall point and type of
signal the Port
should hoist.
19
FISHERIES WARNINGS
Criteria
1.
2.
3.
4.
Strong off-shore and on-shore winds (or with appropriate direction),
speed exceeding 45 kmph
SQUALLY Weather – Frequent Squalls with rain; or persistent type of
strong gusty winds (>20kts; 36kmph) accompanied by rain.
Gales
State of sea very rough or above.
Information
1.
2.
3.
Through ports
XXW landline telegrams to fisheries officials and
AIR broadcast daily three / four times in local language.
Bulletin contains information about
1.
2.
3.
Synoptic situation
Signals hoisted and
Advice not to go out in to the sea.
20
CYCLONE PREPAREDNESS
BEFORE CYCLONE (WHEN EXPECTED)
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Check doors, windows, bolts etc., Fix glass windows if loose.
Check defects in tiled/sheets roof.
Clean loose metal tins/sheets around house.
Shift from very old/damaged house.
Keep radio with batteries to hear cyclone warnings.
Store Kerosene, keep ready lamps, candles, match sticks,
battery lights etc.
Store drinking water and provisions for a week. Ready to
eat/easy to cook foods will further help in such situations.
Move to cyclone shelters if necessary. Move cattle to safety,
secure boats & nets.
Be optimistic and prepared for cyclone.
Give adequate weightage for Cyclone Warnings even if no wind
or rain is present. Some cyclones move fast and cause great
damages.
21
CYCLONE PREPAREDNESS
1.
2.
3.
4.
DURING CYCLONE
Don’t be afraid. Hear to Cyclone Warnings. Don’t
spread rumors.
Don’t move around outside. Don’t leave cyclone
shelters till told to do so.
Don’t open doors and windows. If required open
windows which are not facing the wind
When cyclone passes over your place it will be
calm and clear during the cyclone eye. Keep
waiting for another spell of bad weather.
22
CYCLONE PREPAREDNESS
1.
2.
3.
4.
5.
AFTER CYCLONE CROSSED
Move out of cyclone shelters after consulting
concerned officers.
Don’t touch electric wires on the way / road.
Inform APSEB officials.
Beware of big trees. Branches may break.
Take vaccines and cholera injections.
Drink water after adding chlorine tablets
23
TSUNAMIS
24
Tsunamis
A series of traveling ocean waves of extremely long length generated
primarily by earthquakes, volcanic eruptions, outer-space meteorite splash or
landslides occurring below or near the ocean floor.
Tsunamis are a threat to life and property for all coastal residents living near
the ocean.
Although 80% of the tsunamis occur in the Pacific, they can also
threaten coastlines of
countries in other regions, including the Indian
Ocean, Mediterranean Sea, Caribbean region, and even the
Atlantic Ocean.
25
MORE ABOUT TSUNAMIS
•Earth quakes of intensity >7 on Richter scale have potential for generating
Tsunami
•Tsunamis travel outward in all directions from the generating area
•In the deep and open ocean, they travel at speeds of 500 to 1,000 kilometers per
hour
•The distance between successive crests can be as much as 500 to 650
kilometers
•In the open ocean, the height of the waves may be no more than 30 to 60
centimeters (1 or 2 feet), and the waves pass unnoticed
•The passing waves produce only a gentle rise and fall of the sea surface.
•Upon reaching shallower water, the speed of the advancing wave diminishes, its
wave length decreases, and its height may increase greatly, owing to the piling up
of water
•Configuration of the coastline, shape of the ocean floor, and character of the
advancing waves play an important role in the destruction wrought by tsunamis
26
TSUNAMI SAFETY RULES
1.
All earthquakes do not cause tsunamis, but many do. When you hear that an
earthquake has occurred, stand by for a tsunami emergency.
2.
An earthquake in your area is a natural tsunami warning. Do not stay in low-lying
coastal areas after a strong earthquake has been felt.
3.
A tsunami is not a single wave, but a series of waves. Stay out of danger areas until
an "all-clear" is issued by competent authority.
4.
Approaching tsunamis are sometimes preceded by a noticeable rise or fall of coastal
water. This is nature's tsunami warning and should be heeded.
5.
Small tsunami at one point on the shore can be extremely large a few miles away.
Don't let the modest size of one make you lose respect for all.
7.
All tsunamis like hurricanes are potentially dangerous, even though they may not
damage every coastline they strike.
8.
Never go down to the shore to watch for a tsunami. When you can see the wave you
are too close to escape it. Never try to surf a tsunami; tsunamis do not curl or break like
surfing waves.
10. During a tsunami emergency, your local civil defense, police, and other emergency
organizations will try to save your life. Give them your fullest cooperation.
27
TSUNAMI Monitoring and EARLY WARNING IN INDIA
•A Network sensors being established by participating countries to share data
•A Multi Departmental setup involving IMD, DOD, DOS etc
•National Tsunami Warning Centre at INCOIS, Hyderabad
•Network if 17 Real Time Seismo Monitoring Stations being installed by IMD
which transmit data to IMD and INCOIS
•12 Nos Bottom Pressure Records being installed in BOB
•50 Nos tide guages being installed along east coast, 8 along AP coast
•Tsunami Modelling (N2 of Japan, MOST by US) to be used to work out quickly
the wave heights, wave speed etc.
•INCOIS processes data and issued warnings to MHA at Delhi
•MHA at Delhi co-ordinates dissemination
28
EARTH QUAKES
29
EARTHQUAKES
ARE ONE OF THE
WORST NATURAL HAZARDS
CAUSING
WIDESPREAD DISASTER AND
LOSS OF HUMAN LIVES
PRIMARILY DUE TO COLLAPSE
OF STRUCTURE
OR
BUILDINGS.
30
EARTHQUAKE MONITORING
• India Meteorological Department Is The National
Agency For Detecting And Locating Arthquakes And
Evaluation Of Seismicity In Different Parts Of The
Country
•A network of Seismological sensors is maintained by
IMD
•National Centre for Earthquakes in IMD HQ receives
realtime data.
•Data is analysed using computer based systems and
parameters like Epicentre, Intensity etc are computed.
•Data disseminated to INCOIS, MHA etc
31
EARTHQUAKE PREDICTION
•NO GLOBALLY ACCEPTED AND APPLICABLE METHOD FOR EARTHQUAKE
PREDICTIONS HAS YET BEEN EVOLVED
•EFFORTS ARE AFOOT TO STUDY VARIOUS PRECURSORY PHENOMENA
WHICH COULD HELP IN DEVELOPING A SCHEME TOWARDS EARTHQUAKE
PREDICTIONS. SOME OF THE PROMISING PRECURSORS ARE:
EARTHQUAKE SWARMS, SEISMIC GAPS, CHANGES IN SEISMIC WAVE
VELOCITY, ELECTRICAL RESISTIVITY, MAGNETIC PROPERTIES, SURFACE
TOPOGRAPHY, RADON MEASUREMENT etc.
32
FLOODS
Floods are mainly triggered by severe thunderstorms, cyclones or
monsoons.
In low-lying coastal areas, storm surges, tsunamis or rivers swollen by
exceptionally high tides can cause flooding.
Floods can threaten human life and property.
Floods affect Agriculture sector
Flood water can become a breeding ground for mosquitoes, tsetse fly creating
an increased risk of malaria, sleeping sickness, typhoid, cholera and dengue
fever outbreak;
33
Monitoring of Floods
• IMD monitors Flood situations through a network 10 Flood Met Offices located in
various states and as per river basins.
• FMOs collect rainfall data from rain gauges of IMD, CWC, State Govt networks and
compute sub-basin wise Aerial Average Precipitation.
•FMOs issue sub-basin wise QPF to CWC.
•CWC issues flood alerts/warnings.
34
DROUGHTS

Classification of droughts

Monitoring drought: Physical, Biological
and Social Indicators

Drought monitoring by IMD

New Initiative : Drought Forecasting
Classification of droughts
 Droughts are commonly classified into four categories
which are mostly based on different parts of the
hydrological cycle.
 Meteorological drought: Droughts generally start with a
lack of precipitation, possibly in combination with high
evapotranspiration, resulting from the natural variability
of the weather. This is called a meteorological drought.
 Agricultural drought : The meteorological drought causes
a lack of soil moisture, which is called a soil moisture
drought and which affects agricultural crops and/or the
natural vegetation. The soil moisture drought is also
frequently called agricultural drought.
Classification of droughts
 Hydrological drought :
 Lack of precipitation may also cause low stream flows:
the stream flow drought. The soil moisture drought
causes a decrease in the amount of recharge, which in
turn causes lower groundwater levels and decreasing
groundwater discharge to the surface water system,
which is a groundwater drought.
 Both the stream flow drought and the groundwater
drought are part of the hydrological drought.
 Socio-economic drought:
 The socio-economic drought expresses the deficit of
water as an economic good and addresses the damage
caused by all the different types of drought.
Measurement/indication of Four different ways
of drought
 Meteorological-a measure of departure of
precipitation from normal. Due to climatic
differences, what might be considered a drought in
one location of the country may not be a drought in
another location.
 Agricultural-refers to a situation where the amount of
moisture in the soil no longer meets the needs of a
particular crop.
 Hydrological-occurs when surface and subsurface
water supplies are below normal.
 Socioeconomic-refers to the situation that occurs
when physical water shortages begin to affect
people.
Classification of droughts
Drought differs from aridity, which is characterized by a dry climate with
low precipitation and high evaporation losses..
Drought characteristics vary significantly from one region to another, e.g., some days
without receiving rainfall in a tropical region might be considered a drought
occurrence, whereas in dry regions a drought may first be recognized after some
years without rain.
Drought at a glance
Sequence of Drought Impacts:
 When drought (i.e. meteorological drought ) begins, the
agricultural sector is usually the first to be affected because of its
heavy dependence on stored soil-water.
 Those who rely on surface water (i.e, reservoirs and lakes) and
subsurface water (i.e,ground water) are usually the last to be
affected.
 A deficit of precipitation has different impacts on the ground water,
reservoir storage, soil moisture, snowpack, and streamflow. Soil
moisture conditions respond to precipitation anomalies on a
relatively short scale, while ground water, streamflow, and reservoir
storage reflect the longer-term precipitation anomalies.
Monitoring drought: Physical, Biological and Social
Indicators
 Physical indicators include
Rainfall, Effective soil moisture, Surface water availability, Depth to
groundwater, etc.
 Biological/ Agricultural indicators comprise
Vegetation cover & composition, Crop & Fodder yield,
Condition of domestic animals, Pest incidence, etc.
 Social indicators are mostly impact indicators and include
Food and Feed availability, Land use conditions,
Livelihood shifts, Migration of population, etc.
 In most cases only those indicators that measure the rainfall needs of
following sectors are considered:
(a) agricultural need,
(b) drinking water supply, and
(c) storage of reservoirs and ground water
Drought monitoring by IMD
 During 1965 and 1966, major parts of India were under
prolonged and severe drought conditions due to
deficient monsoon rainfall.
 On the recommendations of the Planning commission,
India Meteorological Department (IMD) has started
Drought Research and monitoring at Pune in 1967.
 IMD monitors drought by using three well established
drought indices. One of which is purely meteorological
drought, the second one is agricultural drought and the
third one started last year covers meteorological,
agricultural as well as hydrological droughts.
1. Percent of Normal
 The percent of normal precipitation is one of the simplest
measurements of rainfall departure/deficiency for a location.
 Analyses using the percent of normal are very effective when used
for a single region or a single season. Percent of normal is also
easily misunderstood and gives different indications of conditions,
depending on the location and season.
 It is calculated by dividing actual precipitation by normal
precipitation i.e. long period average and multiplying by 100%.
 This can be calculated for a variety of time scales. Usually these
time scales range from a single month to a group of months
representing a particular season, to an annual or water year.
Normal precipitation for a specific location is considered to be
100%.
IMD Criteria on meteorological drought
IMD describes meteorological drought from rainfall departure from
its long term averages (normal) and declares meteorological
drought on SEASONAL basis for a geographical region.
Departure of actual rainfall from normal (%)
-26 to –49
Moderate drought
-50 or more
Severe drought
In India, a year is considered to be a DROUGHT YEAR in case the area
affected by moderate and severe drought, either individually or
together, is 20 - 40 % of the total area of the country and seasonal
rainfall deficiency during south-west monsoon season for the country
as a whole is at least 10% or more. When the spatial coverage of
drought is more than 40% it will be called as ALL INDIA SEVERE
DROUGHT
Merit :
Simplicity makes this index popular in India.
Demerit : Average precipitation is not always the same as median
precipitation.
Rainfall Monitoring by IMD
 India Meteorological Department through it’s wide network
of observations (around 3000 rain gauges) routinely
monitor rainfall situation over the country throughout the
year in different spatial scales
(districts/states/meteorological subdivisions and all India)
in daily/weekly/monthly/seasonal scales and prepares
rainfall reports for the use of different state/central
government agencies.
 Hopefully we can start monitoring rainfall situation eve
taluka/block level
Rainfall Monitoring in met subdivision scale
Monthly scale
Weekly scale
Seasonal scale
Daily time scale
Weekly time scale
Seasonal time scale 2014
SW
Rainfall Departures in Monsoon 2014
Specified period
Cumulative period
Actual
Normal
Dep(%)
Actual
Normal
Dep(%)
ANDHRA PRADESH
0.5
5.5
-92
435.2
609
-29
COASTAL ANDHRA PRADESH
EAST GODAVARI
0
7.6
-100
397.3
703.9
-44
GUNTUR
0.4
6
-94
411.2
543
-24
KRISHNA
0.1
5.9
-99
373.2
701.4
-47
NELLORE
1.1
6.9
-84
298.3
352.4
-15
PRAKASAM
1.6
5.7
-72
262.7
382.5
-31
SRIKAKULAM
0
6.5
-100
805.4
745.7
8
VISHAKHAPATNAM
0
6.3
-100
588
674.4
-13
VIZIANAGARAM
0
5.3
-100
721.8
726.1
-1
WEST GODAVARI
1.2
5.2
-77
637.6
783.9
-19
SUBDIVISION RAINFALL
0.6
6.2
-90
448.7
580.8
-23
RAYALASEEMA
ANANTAPUR
0.3
6
-95
213.4
322.8
-34
CHITTOOR
0.2
7.7
-98
314.4
417.1
-25
CUDDAPAH
0
6.3
-100
266.9
404.1
-34
KURNOOL
0
5.6
-100
442.9
460.2
-4
SUBDIVISION RAINFALL
0.1
6.3
-98
308.6
398.6
-23
TELANGANA
ADILABAD
0
4.2
-100
683.1
958.9
-29
HYDERABAD
0
4.4
-100
423.3
643.5
-34
KARIMNAGAR
0
4.2
-100
571.8
800.3
-29
KHAMMAM
0.5
4.5
-88
616
860.4
-28
MAHBUBNAGAR
0
4.1
-100
421
559.7
-25
MEDAK
0.2
4.5
-96
330.5
743.9
-56
NALGONDA
3
5.9
-50
345.8
554.7
-38
NIZAMABAD
0
5.9
-100
440.7
920.1
-52
RANGAREDDY
0.1
3.8
-96
414.4
653.7
-37
WARANGAL
0.6
3.6
-83
546.1
796.6
-31
SUBDIVISION RAINFALL
0.5
4.5
-88
498.5
755.1
-34
In CAP
SRK,VZM & VSK
Normal rainfall
Remaining
Districts Moderate
Drought
In RYSM
KRN
Normal rainfall
Remaining
Districts Moderate
Drought
In TLNG
MDK & NZB Severe
Drought
Remaining
Districts Moderate
Drought
Areas and dates of high impact weather events during the 2014southwest monsoon
.
Rainfall Monitoring in District scale
Seasonal scale
Weekly scale
All India southwest monsoon rainfall and percentage of
districts affecting drought during 2003-2013
Year
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
ALL India SW monsoon Moderate
RF % Departure from Drought (%
normal
Districts)
2.3
14.4
-13.8
28.7
-1.3
20.1
-0.4
29.1
5.7
17.8
-1.7
14.3
-21.8
42.4
2
22.8
1.6
16.1
-7.1
27.6
5.6
18.1
Severe
Drought
of
(%
Districts)
4.7
7.2
3.4
6.1
5.6
3.4
11.1
4.2
2.5
8.0
5.8
of
Every year even in good monsoon year more
than 15 % of the districts (80-85 districts) of
India experience drought
Agricultural drought
IMD monitors agricultural drought on a real-time basis during the
main crop seasons (kharif and rabi) of India using Aridity Anomaly
Index.
 Based on the aridity index, Biweekly Aridity Anomaly Reports and
maps for Southwest Monsoon Season for the whole country and
for Northeast Monsoon Season for the five meteorological
sub-divisions, viz. coastal Andhra Pradesh, Rayalaseema, south
Interior Karnataka, Tamil Nadu & Pondicherry and Kerala are
prepared.
 These maps are sent to Ministry of Agriculture and Co-operation,
New Delhi and other government agencies on operational basis for
the use in Agricultural Planning and advisory.
 The maps are also routinely uploaded in IMD website
Aridity Anomaly Index (contd..)
Aridity index (AI) is developed on the lines of Thornthwaite’s concept to
monitor the incidence, spread, intensification, and recession of drought.
Real time rainfall for about 210 stations network in considered for
calculating Aridity index. AI is given as ─
PE - AE
AI = ----------- × 100
PE
where PE is potential evapotranspiration calculated with the help of Penman’s
formula, which takes into account mean temperature, incoming solar
radiation, relative humidity, and wind speed.
 AE
is actual evapotranspiration calculated according to Thornthwaite’s
water balance technique, taking into account of actual rainfall, and field
capacity of the soil.
Aridity Anomaly Index (contd..)
 The Normal Aridity Indices (NAI) are calculated using
the climate normal values.

Aridity anomalies (Actual - Normal) are worked
out and classified into various categories of aridity
conditions viz. 'mild', 'moderate' and 'severe' for
monitoring and assessment of agricultural droughts
over the country.
The arid areas are demarcated as follows:
Aridity Anomaly
0 or negative
1 – 25
26-50
> 50
Areas
Non-arid
Mild arid
Moderate arid
Severe arid
Aridity Anomaly Index (contd..)
With the help of aridity anomalies, crop stress conditions in
various parts of the country can be monitored during the
monsoon season. These anomalies can be used for crop
planning and in the early warning system during
drought/desertification.
This is an useful index for monitoring agricultural drought at
15 days interval.
Aridity Anomaly Maps during Southwest
Monsoon Season 2013
Thank You