Monsoon Woes Recorded in the Caves

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 Historical documents and also other proxy records of vegetation, pollen and spores and tree ring analysis have been in vogue as proxy records of the past climates.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.


More by :  V. K. Joshi (Bijji)

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