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Whats happening to the monsoon?
N. Gopal Raj
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Researchers are noticing changes in the established patterns of
monsoon rainfall.
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Photo: PTI
still Hopeful: The contribution of July rainfall to the annual
rainfall showed amarked decline.
Last year, heavy rains in southern India led to the south-west
monsoon ending withabove-average nationwide rainfall. In striking
contrast, this year large parts ofthe south as well as Maharashtra
and Gujarat are suffering a drought. While Juneended with surplus
rains for the country as a whole, poor rains in July havepushed the
national average into a deficit.
Upto July 15 this year, the south had received 34 per cent less
rain than usualwhile central India had a deficit of three per cent,
according to the IndiaMeteorological Department (IMD). The
north-western States, which fared badly lastyear, had a surplus of
77 per cent by mid-July. The eastern parts of the countrytoo have
been getting ample rain.
Rain is never evenly distributed across the country during the
monsoon. Indeed, ashas happened this year, parts of the country can
be flooded after receiving toomuch rain while other places bake in
the sun. Predicting how various regions ofthe country will fare
during a monsoon is hugely problematic. But over longperiods of
time, some typical patterns emerge. The north-eastern states and
thewest coast, for instance, usually get plenty of rain each year
while places likeRajasthan get far less of it and are
drought-prone.
However, some researchers are noticing changes in the
established patterns ofmonsoon rainfall.
India receives about three-quarters of its annual rainfall
during the south-westmonsoon. Data for the last 100 years shows
that close to one-third of thenationwide monsoon rainfall occurs in
July. August gets around 29 per cent of allthe monsoon rain while
June and September each receive about 19 per cent.
But when P. Guhathakurta and M. Rajeevan of the IMDs National
Climate Centreclosely analysed the rainfall distribution between
1901 and 2003, they found that
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the contribution of June and August to the annual rainfall
exhibited significantincreasing trends. The contribution of July
rainfall, on the other hand, showed amarked decline.
In addition, there were strong regional patterns to this change.
The contributionof June rainfall had gone up all along the western
side of the country while ithad fallen in some central and eastern
parts. The contribution of July rainfallhad reduced in central and
west peninsular India, covering much of Karnataka and
Maharashtra, the Konkan-Goa region, and eastern Madhya Pradesh.
Interestingly, thesame regions were receiving more rain than before
in August.
Over the last 10 years or so, July rainfall has often been below
par, remarked Dr.Rajeevan, who recently moved to the National
Atmospheric Research Laboratory atTirupati in Andhra Pradesh. But
neither the annual rainfall nor the rains duringthe south-west
monsoon for the country as a whole showed any clear trend either
ofincrease or decrease, he added.
However, Dr. Guhathakurta and Dr. Rajeevan noted in their paper
that Jharkhand,Chhattisgarh and Kerala were now getting
significantly less rain than beforeduring the south-west monsoon.
On the other hand, much of West Bengal, west UttarPradesh, Jammu
& Kashmir, Konkan and Goa as well as parts of Maharashra and
Andhra
Pradesh were getting more rain during the monsoon.
Meanwhile, K. Krishna Kumar of the Indian Institute of Tropical
Meteorology inPune is finding that the annual cycle of rainfall is
beginning some two weeksearlier than before across much of northern
India in the last two to threedecades.
Places where the monsoon used to set in only at the end of June
now regularly getrain much earlier in the month, he told The-Hindu.
This year was a classic caseof many places in northern India
receiving a lot of rain in June itself.
Prominent shifts
In many northern states, the May-June rainfall has been
increasing in recentdecades while the July-August rainfall has
declined. These shifts have beenparticularly prominent in the
north-western and eastern parts of the country, headded.
Dr. Krishna Kumar is working with Balaji Rajagopalan of the
University of Coloradoat Boulder in the United States to try and
understand why these changes areoccurring. Global warming by itself
does not appear to explain the changes,observed Dr. Krishna
Kumar.
Research carried out for a Masters thesis at the Indian
Institute of Science tooindicated that the annual cycle of rainfall
could be changing in central India
over the last two decades. In her thesis, Charu Singh used
mathematical techniquesto define the rainy period and its salient
characteristics. Her work suggestedthat the rainy period in central
India could be ending earlier and that theduration of the rains
might therefore be somewhat shorter than before. These,however,
were only preliminary findings and more work was being done to make
sureof their robustness, cautioned her thesis supervisor, V.
Venugopal.
Whatever be the underlying reasons, as Dr. Krishna Kumar points
out, such changesin rainfall patterns will have profound
implications for farmers and the cropsthey are able to grow.
