rainfall in kerla

8/8/2019 Rainfall in Kerla

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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

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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

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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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rainfall in kerla

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