Indian
economy sustains on monsoon. A good monsoon ushers happiness for one and
all from the farmers to politicians. A good monsoon means crops to the
farmer and his bread and butter for the year, more earnings for the
businessmen; even the stock exchange shows a rise and stability for the
ruling political party. The relationship of the monsoon and the farmer
is perhaps as old as the development of the agrarian society in our
country.
Each year the
weathermen make forecasts about the monsoon based on several parameters
and mathematical modeling. Often the forecasts fail sometimes leading to
suicide by the farmers and the ruling government has to face the public
flak. Since it is everyone's problem it has been bothering the
climatologists and the geologists alike. Geologists rely on past
experiences to visualize the possible future conditions. Thus past
chapters of the climate are always invaluable for the future
predictions.
Problem
in knowing about the past climates is that though an instrumental
record of past 150 years is available but beyond that there is no
scientific record as such. Historical documents and also other proxy
records of vegetation, pollen and spores and tree ring analysis have
been in vogue as proxy records of the past climates. These records,
though not very precise did help the scientists is working out the
past climate patterns on centennial or decadal scales. In the past
decade development of refined instruments to date the rocks and to
study the oxygen isotopes from the rocks revolutionized the concepts
of studying the patterns of past climates.
Recently Ashish Sinha of Department of Earth Sciences, California
State University, Dominguez Hills, Carson California; K.G.
Cannariato and Lowell D. Scott of Department of earth Sciences,
University of Southern California, L.A. California, USA; Hai Cheng
and R. Lawrence Edwards of Department of Geology, and Geophysics,
University of Minnesota, Minneapolis, Minnesota, USA; M.G. Yadav of
Physical Research Laboratory (PRL), Ahmedabad, India and Indra Bir
Singh, Department of Geology, Lucknow University, Lucknow, India
published an interesting paper in Geophysical Research Letters (34,
L16707, doi:10.1029/2007/GL030431) narrating their findings on the
monsoon pattern of 900 years between 600 to 1500 AD.
This international collaboration between the scientists brought to
light many hitherto unknown facts. For example they were able to
establish a correlation between the past famines and social unrest
during the above period with the rainfall. The story develops around
a stalagmite, normally taken as a freak of nature and it is really
amazing to know how much information an inanimate object like a
stalagmite can hold!
Famines have been a part of the Indian society since ages. As late
as late 1960s El Nino related Indian Summer Monsoon (ISM) failure
for consecutive three years led to 1.5 million deaths says Sinha.
Problem due to mismanagement of storage of grains for emergencies
was overcome and the famines on large scale ended. The famines were
overcome with better planning, but the problem of the farmers
remained the same. The southwest ISM contributes to 80% of seasonal
rainfall of Southeast Asia each year. A disruption of pattern and
large tracts go dry. The cropping pattern is based upon the monsoon
and if the rain god is angry the poor farmer has no other recourse
but to starve.
In order to assess the future of rainfall a past record is a great
help. But a record of mere 150 years (instrumental record) is not
enough to postulate the future rainfall patterns. Recently
speleothems (stalagmites) have gained significance as excellent
archives of past monsoons. W. Dansgaard of Geophysical Isotope
laboratory in Copenhagen had established in 1964 the significance of
stable isotopes in precipitation of water. We know the stalagmites
in the wombs of the limestone caves are nothing but precipitates of
water over thousands of years. Thus Dansgaard had revolutionized the
very concept of studying the rates of precipitation of water with
the help of oxygen isotopes.
Taking cue from this work researchers like S. Burns and his
co-workers established a 780 year old record of Indian Ocean monsoon
precipitation from a speleothem from Oman in 2002 in Journal of
Geophysical Research; D. Fleitmann and his co-workers also reported
Holocene (past10000 years) forcing of ISM from same area in 2003 in
Nature and A. Sinha and co-researchers reported the variability of
past ISM based on isotope studies in 2005 in 'Geology'.
The present record of Sinha becomes interesting and significant as
it opens up a yearly record from the pages of the history of monsoon
from a Speleothem from Dandak caves.
In order to know about Dandak caves readers are requested to turn
back the pages of boloji.com and read the article 'Secrets of
mystery caves' published on 27th May, 2007. Briefly these caves are
located in Kanger valley National Park in Bastar district of
Chattisgarh. The area is densely forested and difficult to approach.
The caves have evidences of inhabitation some 5042-5318 Cal years
B.P. in the form of trace of hearth fire and seeds. No bones have
yet been discovered. Stalagmites are abundant in these caves and
they lured the geologists.
Dandak area falls in the core of the ISM. The proxy methods used for
studying ISM also included the marine sediments of the Arabian Sea.
Problem with those sediments is that the results do not match with
the core area like Dandak. Country's 75% population lives in the
core area, and sustains on agriculture. Thus the study of monsoon
over such area becomes all the more significant.
In order to establish the authenticity of the rainfall pattern
obtained from the speleothems, Ashish and his friends compared their
results with the past instrumental records available from the
nearest meteorological station at Jagdalpur. It was found that the
results show a strong correlation with the instrumental records of
past one century.
Dandak Cave consists of two chambers connected by a low, narrow
tunnel. One has to crawl through to cut across. A stalagmite 27 cm
high from this narrow passage at a distance of ~220 m from the cave
entrance caught the fancy of the geologists and was collected. Such
spots are least contaminated by external sources. That is why the
fancy. The stalagmite layers were separated in the laboratory and
Dated with the help of Uranium and Thorium isotopes in them. The
dates obtained and the information on rainfall patterns gathered via
the percentage of oxygen isotope δ18 O gave amazing results.
Here it is pertinent to mention that the value of δ18 O is inversely
proportionate to rainfall. Based on them they found two prolonged
periods in which the annual rainfall fell by about 30%. Thus there
was a period of famine and drought that lasted for 30 years in 14th
century (1350 AD onwards) and 15 years in 15th century. Both periods
correlate with devastating historical famines buried in the pages of
the history. Their study has also brought to fore 'Durga Devi famine
of Mahrashtra which lasted for 11 years at the turn of the 14th
century. The century must have been a real dreadful century for the
human and animal life on our sub-continent! Sinha says, 'Our results
suggest that the instrumental record seriously underestimates the
magnitude of monsoon variability, and that in the past extreme
droughts occurred relatively frequently, or for extended period of
time.'
The period from ca 1400 to 1850 AD is known as the Little Ice age (LIA).
This was a repetition of the earlier Ice Ages with a smaller extent.
The LIA had almost brought life on the affected areas to a
standstill. Consequent to the beginning of the warm phase the human
population in the Indian monsoon region has soared from 200 million
to over one billion. It means if there is a recurrence of a weak
monsoon as it had happened in the past centuries, the affect of the
humanity would be tremendous. The economic sustainability of the
region plus the life both would be at stake.
The report of Dr Ashish Sinha and his co-workers should not be taken
as a mere academic addition, but it should be an eye-opener for the
planners and executives to create more sustainable land-use patterns
and water management. We do not know about the future but we
certainly know that the nature always repeats the past events from
time to time. It is time to take the past warnings seriously.
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