There may be differences about the cause of climate change and related issues, but it is a fact that global climate is set to change. And it is not for the first time it is happening. It has happened several times in the geological past and also during the hominid (human ancestors) and human evolution and history. Several civilizations flourished and then suddenly vanished because of environmental factors. Past droughts forced man to develop ways and means of storing rainwater - which we now call as Rainwater Harvesting. Extremes of climate like sudden floods, drought, heat wave, cyclone, story rainfall or hurricane leave a greater impact on the human society than gradual climate change. Realising the significance of climatic impacts on cultures D.N. Pandey, of Indian Institute of Forest Management, Bhopal, A.K. Gupta, IIT Kharagpur and Davi M. Anderson of University of Colorado, USA reviewed the human adaptations world over to meet the climate vicissitudes and particularly the rainwater harvesting practices in India in a paper in the Current Science. Here is a report.
It is known to everyone that in the historical past civilsations vanished, people were dislocated due to prolonged drought. There was widespread migration of human beings to safer areas. Even in those primitive years some communities resorted to rainwater harvesting and survived the vagaries of weather while those who didn’t, migrate and or perished. But in those eras scientific thought had not emerged and technology was not there in the present form. Now armed with best scientific data and information and technology to meet any challenge instead of fleeing the areas in times of severe prolonged droughts better strategies can be used to harness rain water for bad times.
Water means life. Since times immemorial our ancestors selected spots close to water bodies as locations for developing habitats. The craving continues-even now ‘River View and Sea Front’ apartments sell like hot cakes. It is worth mentioning that Hominids the precursors of the humans preferred to live around water bodies some 6 and 7 million years ago. Modern humans evolved around 150000 years ago. By then they knew very well the significance of water bodies. They got their food (game) easily near water holes, rivers acted as means of traveling apart from the availability of water for drinking and later on when they began to sow, they developed techniques for irrigation as well.
Once the hunter-gatherer humans discovered the secret of sowing, they intuitionally developed an uncanny sense about the ups and downs of climate. They also developed ways and means to adapt according to climatic vicissitudes. Climate change and rainwater harvesting practices have been going on in India since times immemorial. However, Pandey and Gupta tried to gather the information and put it in a chronological order to show how the society adapted and faced the climate change since 4500 B.C.
In a scientific review one can not depend upon only the historical records. Corroborating scientific evidence is also necessary. Pandey and Gupta collected multi-proxy collateral data to decipher the climate change in the past 10000 years. Globigerina, a marine microfossil is often used for measuring the oxygen isotope 18O content in the shells. This helps in recreating a picture of climatic fluctuations (especially the temperature changes) in the history and prehistory. It is the climate history of past ~11000 years which matters most to us, because it was during this period humans faced the maximum brunt of climate changes. Extreme climate events like aridity, drought, flood, cyclones, stormy rainfall happened routinely during these tears. But a unique cold spell also known as the Little Ice Age (1300-1850AD) makes one ponder about the scare of global warming. Earlier article Return of the Ice Age elaborates the details of its impact especially in the Himalayan Region.
The Little Ice Age reduced the subtropical sea-surface temperatures by 3 to 4 degrees centigrade. Studies have revealed that these climate shifts of extreme cold or heat have occurred in a cyclic pattern almost 1470 plus-minus 500 years. Such changes in the past 11000 years have highly influenced evolution of cultural diversity, domestication of medicinal plants, crops and animals and adaptive innovations through socio-economic development in human history, say Gupta and Davi.
Climate has had a tremendous influence on our cultures in the past 11000 year (Holocene). Laguna Pallacacocha in southern Ecuador has sediments which speak aloud about El Nino Southern Oscillation or ENSO variability on a millennial scale, throughout the Holocene. During the pre-historic era a monumental temple construction activity started on the Peruvian coast some 5,8000 years ago. Due to an increase in El Nino frequency some 3200 to 2800 years ago the construction of monumental temples was abandoned. This was just an example. Asia, Africa, North America and South America had had their share of several extreme arid events and droughts. But all major events had taken place much before the industrial revolution of 1850. In the recent years Green House Gas forcing due to oceanic changes caused droughts during 1998-2002 period over the Northern Hemisphere and mid-latitudes across the United States, the Mediterranean, southern Europe and Southwest and Central Asia. These droughts again were due to oceanic changes and not merely due to anthropogenic impacts. Pandey and his co-workers conclude that during the 20th century terrestrial temperatures may have been higher because of natural variability.
Whenever arid events have taken place in the past the society switched over to water harvesting, including rainwater harvesting. Our ancestors may not have been scientists, but they had enough common sense about conserving water for the posterity. For example, 10 to 8000 years ago the southwest monsoon was quite powerful and active. But it began to weaken in the past 8000 years.
The remnants of primitive water harvesting structures found in the Thar Desert in Rajasthan, dated to be 4500BC point to the human intelligence and innovativeness for saving water in a land turning to be water scarce. There was further weakening of southwest monsoon in 2600 BC as a result people in Dholavira (Harappan civilization) developed large open tanks as rainwater harvesting structures. Similarly during 2300 to 1750 BC Urban Harappan Civilization developed earliest wells. They were rich people because they had stored enough rain water in tanks and made conjunctive use of the wells for irrigation.
The list of rain water harvesting techniques adopted through the ages is endless and each date coincides with a prolonged drought. Climate fluctuations in the past few thousand years may have given rise to traditional village tanks, ponds and earthen embankments numbering more than 1.5 million that still harvest rainwater in 660, 000 villages in India say Pandey and his co-researchers. Ancient Indian texts like Rigveda (1500BC), Atharva Veda (800BC), Kautilya’s Arthashastra (300 BC), Varahmirira’s Brihatsamhita (AD 550) and Kalhan’s Rajtarangini (AD 11548-1150) reveal the emphasis given to rainwater harvesting systems in the years of the yore. It is also seen from geological evidences that during the periods when rainwater harvesting was been emphasized there have been prolonged droughts or arid phases.
Today rainwater harvesting appears to be most practical and sound way of conservation of water. Quoting R.B Jackson et al Pandey says there are several reasons to support this contention, such as; over one half of the accessible freshwater runoff globally is already appropriated for human use; more than 1 X 109 people currently lack access to clean drinking water and almost 3 x 109 people currently lack basic sanitation services; because the human population will grow faster than increases in the amount of accessible freshwater, per capita availability of fresh water will decrease in the coming century; the climate change will cause a general intensification of the earth’s hydrological cycle in the next 100 years, with generally increased precipitation and evapotranspiration. New dams that will come up in the next 30 years will increase accessible runoff by about 10%, whereas the population is projected to increase by more than 45% during that period. Thus except rainwater harvesting there seems to be no other sound alternative to survive on this planet.
Demand of water for drinking and recreation has increased and in that race there is less water available for food production. Rain god is not going to be happy anymore and one should expect erratic rainfall-sudden, heavy downpours likely to occur more and sudden droughts in some regions can not be ruled out.
India has faced such erratic upheavals of climate in the historic past as well. That is why we have rainwater harvesting systems since early times. The havelis of Jabalpur, (M.P.) bandh and bandhulia of Satna, (M.P.), virda of Gujarat, khadins of Rajasthan, ahar-pynes of Bihar, eri of Tamil Nadu and dhora of Aravalis and similar other earthworks found throughout the country speak about the ingenuity and foresight of our ancestors. The sediment cores of these ancient rainwater harvesting systems need to be studied using 14C dating so that a precise relationship between the ancient practices and climate relationship could be established.
Traditional systems may have been very effective in the days of the yore, but those now combined with modern techniques water harvesting can be made a fruitful tool to save the humanity and other organisms and plants from dying for want of water. It is better to catch the bull by horns, rather than meet a gory end!
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