INDIA METEOROLOGICAL DEPARTMENT
(BHARAT MAUSAM VIGYAN VIBHAG)
SOUTH-WEST MONSOON 2000-AN END OF THE SEASON REPORT
An end-of-the-season assessment of the performance of southwest monsoon during the period 1 June to 30 September, 2000 is given below:
For the country as a whole, the rainfall during the south-west monsoon (June-September 2000) has been normal making the year 2000 the 12th successive normal monsoon year. Quantitatively, the rainfall for the monsoon season as compared to the long-period average was as follows:
Country as a whole : 92%
North-East India : 96%
North- West India : 95%
Peninsular India : 89%
The normal date of onset of the southwest monsoon over Kerala is 1 June. This year, the monsoon advanced over Kerala on its normal date as per IMD's prediction. With the formation of a low pressure area in the Bay of Bengal and its movement over land, the monsoon advanced rapidly into South Peninsula, Maharashtra, Orissa, northeastern States, West Bengal & Sikkim, Bihar and some parts of Madhya Pradesh, Uttar Pradesh and Himachal Pradesh by 9 June. The further progress of the monsoon started on 23 June and it covered the entire country on 2 July, about a fortnight earlier than the normal date.
The performance of the monsoon rainfall over the country is monitored by evaluating the departures from the normal rainfall for each meteorological sub-division and district. The rainfall is classified as excess, normal, deficient or scanty as per the following criteria based upon the departure from normal:
Excess : +20% or more
Normal : +19% to -19%
Deficient : -20% to -59%
Scanty : -60% to -99%
At the end of the monsoon season, 28 out of 35 meteorological sub-divisions, covering 70% area and 66% districts of the country received normal to excess rainfall ( Fig. 1 and Table 1 ). The following meteorological sub-divisions received deficient rainfall:
Saurashtra & Kutch ( -44% )
West Madhya Pradesh ( -35% )
Andaman & Nicobar Islands ( -31% )
Gujarat Region ( -31% )
East Rajasthan ( -30% )
East Madhya Pradesh ( -28% )
West Rajasthan ( -22% )
The number of meteorological sub-divisions and percentage of districts with excess/normal rainfall during monsoon for the period 1991 to 2000 is shown in Fig 2(a) and 2(b) respectively. This year's situation is comparable with that of 1991 and 1999.
During this monsoon season, a total of 15 low pressure areas were formed. Of these 11 developed over the Bay of Bengal and moved inland, giving good rains over eastern and peninsular India. Out of these, 5 low pressure areas formed in the west central Bay and crossed into Orissa-Andhra Pradesh Coasts. This movement resulted in normal/excess rains over the peninsula.
One of the low pressure areas in the west central Bay became organised on 22 August and concentrated into a depression that crossed Andhra Pradesh coast on the night of 23 August near Kakinada. Exceptionally heavy rains were reported from isolated places in Andhra Pradesh in association with this system that led to severe flood situation. Flooding also occurred in some areas of East Uttar Pradesh, Bihar and West Bengal in the month of September.
A well marked low formed over northwest Bay off West Bengal coast on 30 August. It crossed West Bengal coast and concentrated into a depression over land over Gangetic West Bengal on 1 September close to Bankura. It moved northwestward and weakened into a low pressure over central Bihar on 3 September. It activated monsoon conditions over Gangetic West Bengal during this period.
Another low pressure system persisted over Bihar and adjoining Gangetic West Bengal on 18 September and became a well marked low over Gangetic West Bengal and neighbourhood on 19 September. Under its influence, monsoon was active/vigorous over this area from 17 to 23 September, and exceptionally heavy falls were experienced, giving rise to severe flooding.
As a consequence of the pattern of development and movement of the low pressure systems and their intensity, the rainfall activity over Rajasthan and Madhya Pradesh remained deficient during the second half of the monsoon season. Gujarat Region and Saurashtra & Kutch, however, did receive some spells of good rain in August, but not in September. Barring this, the rainfall distribution over the country has not been marked by prolonged dry spells.
5. WITHDRAWAL OF MONSOON
The southwest monsoon withdrew from west Rajasthan and some parts of Kutch on 13 September 2000. It further withdrew from Jammu & Kashmir, Himachal Pradesh, Punjab, Haryana, rest of Rajasthan, Gujarat, most parts of Madhya Pradesh, Uttar Pradesh, some parts of Bihar Plains and most parts of north Maharashtra by 29 September. Further withdrawal of monsoon is likely to take place as per its normal schedule.
India Meteorological Department issued its operational Long Range Forecast for the southwest monsoon season of 2000 on 25 May 2000 which was as follows:
( a ) In 2000, the rainfall over the country as a whole for the entire southwest monsoon season ( June to September ) is likely to be normal, thus making the year 2000 the 12th normal monsoon year in succession. The normal is defined as rainfall within ± 10% of its long period average.
( b ) Qualitatively, the rainfall over the country as a whole for the southwest monsoon is likely to be 99% of its long period average with an estimated model error of ± 4%.
( c ) Over the broad homogeneous regions of India the rainfall for the 2000 southwest monsoon season is likely to be 102% of its long period average ( LPA ) over Northwest India, 98% of the LPA over the Peninsula and 100% of the LPA over Northeast India, with an estimated model error of ± 8%.
The monsoon rainfall over the country as a whole during June to September, 2000 was normal ( 92% of its long period average value ). The realised rainfall in northeast India ( 96% ) and northwest India ( 95% ) has been within the predicted limits. However, the rainfall in Peninsular India and for the country as a whole has been marginally on the lower side of prediction.
During the southwest monsoon season of 2000 ( June to September ), 28 out of 35 meteorological sub-divisions covering 70% area and 66% districts of the country received normal to excess rainfall. Seven meteorological sub-divisions received deficient rainfall. As meteorological drought is defined as a large-scale rainfall deficiency of more than 25 %, Gujarat Region, Saurashtra & Kutch, East & West Madhya Pradesh and East Rajasthan fall under this category.
For the country as a whole, the total rainfall during the entire season was 92% of its long period average value, making 2000 the 12th successive normal monsoon year.
only in 3 meteorological Sub-divisions, namely Kerala ( -21% ),
and Lakhshadweep ( -24% ).
The rainfall realised during the season was as follow:
Country as a whole : 92% of L.P.A
Northwest India : 97% of L.P.A
Northeast India : 95% of L.P.A
Peninsular India : 89% of L.P.A