THE SEASON OF RETREATING MONSOON & THE DISTRIBUTION OF RAINFALL IN INDIA TEMPERATURE PRESSURE AND WINDS CYCLONES PRECIPITATION AREAS OF HEAVY, MODERATE AND SCANTY RAINFALL IN INDIA

INTRODUCTION THE MONTHS OF OCTOBER AND NOVEMBER ARE KNOWN AS THE SEASON OF RETREATING MONSOON. DURING THIS SEASON THE TEMPERATURE IN THE NORTHERN PLAINS BEGINS TO DECREASE BECAUSE THE SUN’S RAYS NO LONGER FALL DIRECTLY AT THE TROPIC OF CANCER. THE LOW PRESSURE TROUGH BECOMES WEAKER AND IS NO LONGER STRONG ENOUGH TO ATTRACT THE MONSOON WINDS. THIS RESULTS IN THE RETREAT OF THE MONSOON.

TEMPERATURE IN THE RETREATING MONSOON THERE IS A MARKED RISE IN TEMPERATURE AND HUMIDITY IS HIGH. DUE TO HIGH TEMPERATURE AND HUMIDITY , THE WEATHER BECOMES OPPRESSIVE. THIS IS COMMONLY KNOWN AS ‘ THE OCTOBER HEAT’.

PRESSURE AND WINDS IN RETREATIN MONSOON AS THE MONSOON RETREATS THE ELONGATED TROUGH OF LOW PRESSURE WHICH ONCE PREVAILED OVER NORTH-WESTERN INDIA GETS TRANSFERRED TO THE CENTRE OF BAY OF BENGAL BY EARLY NOVEMBER. THIS IS THE SEASON WHEN SOUTH-WEST MONSOON GIVE PLACE TO THE NORTH –EAST MONSOONS.

CYCLONES IN THE RETREATING MONSOON CYCLONIC DEPRESSIONS ORIGINATE OVER THE ANDAMAN SEA. AREAS MOST VULNERABLE TO THESE CYCLONES ARE THE COASTAL PARTS OF TAMIL NADU, ANDHRA PRADESH AND BANGLADESH.

PRECIPITATION IN RETREATING MONSOON MOST PARTS OF INDIA REMAIN DRY IN THE RETREATING MONSOON SEASON. OOTY, KERALA, TAMIL NADU,AND ANDHRA PRADESH RECEIVE RAINFALL. THE NORTH-EAST MONSOON WINDS ABSORB MOISTURE WHILE PASSING OVER THE BAY OF BENGAL AND CAUSE RAIN IN THE SOUTH- EASTERN COAST OF INDIA.

DISTRIBUTION OF RAINFALL IN INDIA

FACTORS ON WHICH THE DISTRIBUTION OF RAINFALL DEPENDS THE RELIEF THE DIRECTION MOISTURE-LADEN WINDS THE PATH OF CYCLONIC DEPRESSION DETERMINED BY PRESSURE GRADIENT.

AREAS OF HEAVY RAINFALL THE WESTERN SLOPES OF THE WESTERN GHATS, THE WESTERN COASTAL PLAINS OF MAHARASHTRA, GOA, KARNATAKA , KERALA, SOUTHERN SLOPES OF THE EASTERN HIMALAYAS, PARTICULARLY THE GARO, KHASI, JAINTIA, PATKAI, NAGA AND LUSHAI HILLS, COMMONLY REFERRED TO AS THE ASSAM HILLS, RECEIVE HEAVY RAINFALL OVER 200 CENTIMETRES.

WESTERN GHAT REGION MOISTURE LADEN WINDS FROM THE ARABIAN SEA BRANCH OF SOUTH- WEST MONSOON ARE FORCED TO RISE BECAUSE OF THE WESTERN GHATS. CONDENSATION AND HEAVY RAINFALL OF MORE THAN 200 cm OCCURS ON THE WINDWARD SIDE OF THE WESTERN GHATS. THE AMOUNT RECEIVED DECREASES NORTHWARDS AND EASTWARDS – THIRUVANANTHAPURAM, GOA, MUMBAI AND CHENNAI IN A DECREASING ORDER. THE ARABIAN SEA BRANCH OF SOUTH-WEST MONSOON, AFTER SHEDDING HEAVY RAINFALL ON THE WINDWARD SIDE[ MANGALORE, GOA, MUMBAI] OF THE WESTERN GHATS, DESCENDS ON THE LEEWARD SIDE. BY THIS TIME VERY LITTLE MOISTURE IS LEFT and therefore, low rainfall occurs in pune, Hyderabad, Bengaluru and Chennai.

Assam region Warm moisture laden south-west monsoon winds from bay of Bengal branch enter into a funnel- shaped depression, but not moisture is lost as it is a humid delta region. The high Himalayas and assam hills force them to rise very high, resulting in heavy rainfall. Cherrapunji and mawsynram situated on the windward slopes of khasi-jaintia range receive more rainfall, whereas shilling on the leeward side of the shilling plateau is the rainshadow area and receives lesser rainfall comparatively.

Moderate rain regions Moderate rainfall of about 100 to 200 CM annually is experienced in the middle ganga valley in bihar, jahrkhand, west Bengal, Orissa, some parts of the western ghats, eastern Maharashtra, Madhya Pradesh, chattisgarh, northern Andhra Pradesh and southern tamil nadu.

Scanty rain regions Scanty rains of 50 to 100 cm Year is received in areas of upper ganga valley, eastern rajasthan, parts of Punjab and Haryana, and jammu Kashmir. The monsoon duration in these areas is very short as these areas are last to receive the rainfall and first to see it retreat. Large parts of the deccan plateau and the indus plain also receive scanty rainfall.

Desert and semi-desert Less than 50 centimetres of rain is experienced in the northern parts of Kashmir, southern Punjab, parts of Haryana, western rajasthan, thar, the kutch peninsula and the rain-shadow region of the western ghats.