rainfall in kerla
TRANSCRIPT
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Presented by,Akash
SatyajeetSarathJewelMerin
Ubaid
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The normal annual rainfall of Kerala is 3,107mm
On an average the number of rainy days is inthe range of 120-140 in a year
annual yield of water in Kerala in a normalyear is around 7,030 crores cubic metres
The utilizable water resource is around 4,200crore cubic metres.
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Two principal rainy season South-west monsoon (June ,September)
North-east monsoon (October , November)
75% of the annual rainfall during the south-west monsoon
25% of the annual rainfall during the south-east monsoon
75% of the annual rainfall during the south-west monsoon in north kerla
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Main rainy season
75% of annual rain contribution
Begins by the end of May or early june next few months are periods of torrential rain
In western Ghat max rain
The southwest monsoon in Kerala lasts till the
end of September
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Also known as the Retreating Monsoon or theReverse monsoons
northeast monsoon hits Kerala during thereturn of the southwest monsoon winds
Starts from October and ends in December
Heavy afternoon rains accompanied by
thunder and lightening Days are warm and humid but there is not
much variation in temperature.
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South West Monsoon in Kerala :
Average Temperature during this season :
Maximum : 30C
Minimum : 19C
Average Rainfall during the season :
2250 - 2500 mm
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North East Monsoon in Kerala:
Average Temperature:
Maximum : 35C
Minimum : 29C
Average Rainfall during the season :
450 - 500 mm
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monsoon rainfall progresses from south tonorth along the west coast
South-west monsoon the primary rain-giving
season North Kerala is in the cyclonic shear area of the
Low level Jet during this monsoon
south Kerala is in the anti cyclonic shear zone
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under weak monsoon conditions there isdivergence over south Kerala causing little orno rain
There is convergence resulting in rain over
north Kerala on many occasions.
25 to 30% of the annual rainfall during the pre-monsoon and north-east monsoon season
Precipitation during pre-monsoon is mainlyfrom thundershowers
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increased thunderstorm activity in the southerntip of Kerala state during this period
March onwards this increases progressively
with the advance of the season
May makes the maximum contribution to therainfall of the pre-monsoon period
south-west monsoon advances over southKerala between 11th and 31st May
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This is a contributory factor for the pronouncedrainfall maximum over south Kerala duringthis season
Most of the rainfall during north-east monsoonis closely associated with the westwardpassage of storms and depressions
T
he tapering shape of the peninsulaand the lower elevation of the Western Ghats in
the south are the main reasons for rainfall during
this season in south Kerala.
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The meteorology of Kerala is profoundly
influenced by its orography.
heavy annual rainfall (> than336 cm) areas arelocated on the windward slope of the Ghats
On the windward side of mountains moist airis forced up the slope
it cools and condenses, leading to precipitation
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These peaks also provide convection points ofinstability
This instability will be triggered when the or
graphic lifting is strong enough to force airparcels to ascend to their level of freeconvection
T
hus heavy rainfall over the windwardslopes depends on stability
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It also depends on wind velocity perpendicularto the mountain range and on the moist staticstability.
Other Factors:-
Punalur, a station in south Kerala, issurrounded by rocky terrain on its four sides
and this station experiences very highthunderstorm activity.
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Areas lie on the leeward slope of the Ghats andstations situated in the Palghat Gap receivevery less mean annual rainfall(
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lack of direct relationship between the height ofa station and its rainfall
There are high altitude stations that receive
below normal rainfall Vythiri (945 m) experiences heavy rainfall
Kuttiyadi (20 m) lie on the windward slope ofthe Western Ghats experience heavy rainfall
both the stations are situated at markedlydifferent elevations
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The spatial variability of mean annualprecipitation depends upon the topographicfactors
Factors are exposure of the station to theprevailing wind, elevation, orientation andslope of the mountain
Manathavady, a high altitude station (900 m),also situated on the windward slope of themountains in north Kerala, receivescomparatively less rainfall
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Nerimangalam (200 m) receives very heavyrainfall during south-west monsoon,
Kumily (1140 m)situated on the windward
valley of the Anamalai receives below normalrainfall
Isolation heats the peaks much faster
than the valleys below which are shaded by themountains
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Vandanmettu in Anamalai, a high altitudestation(900 m) lying in a valley which receivesrelatively less of rainfall.
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Southern Hill top Tropical Evergreen Forest:
This type of forest abounds in the Andamansand Western Ghats
reaching to a maximum height of only 10 m
Locality factors:
High winds, less favourable soil and climatic
conditions restrict the formation of a climax Rainfall is usually high, over 4500 mm
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Enjoys a wide distribution over the WesternGhats
These are dense evergreen forests with lofty
trees of 45 m or more height.
It is seen in an altitudinal range of about 250-1200 m
The rainfall varies from 1500-5000mm.
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wet evergreen forests are mostly confined tothe windward side of the WG
low (0-800m), medium (800-1450m) and high
(1400-1800m) altitude
The medium elevation forests in some placesmay appear at lower elevation (650 m ) due tolocal variations in the moisture and exposure.
the rainfall is above 2000mm.
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Primary deciduous forests are found in isolatedpatches between the Anamalai and Wayanadplateaus
Denser part of this type is the form ofwoodland and savanna woodland
The rainfall varies from 875 mm 1125mm ondry sites and soils
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The percentage discharge during SW monsoondecreases steadily from north to south
The percentage discharge during SW monsoon
decreases steadily from north to south
the northeast (NE) monsoon yields about 14 %discharge for the rivers from NZ, whereas thepercentage increases to 32 % for the SZ rivers
The Muvattupuzha river shows 23 % yieldduring non-monsoon season
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