and Rainwater Harvesting
| Holocene (~ 11 kyr
BP to present) climate fluctuations, including large spatial variation in Holocene
monsoon and temperature over
India are now well-resolved from various climate change proxies. A somewhat coherent,
although unresolved, picture that emerges for India is as follows: as the aridity
increased in the region as is evident from palaeoclimatic studies, people intensified
rainwater harvesting as is seen from archaeological and historical evidences.
Folk sayings such as ‘capture rain
where it falls’ may have originated in response to the increased aridity in the
Indian region over the last few millennia. Such climate fluctuations 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 and encourage growth of vegetation in commons and agro-ecosystems.(Deep Narayan
Pandey, et al, CURRENT SCIENCE,
VOL. 85, NO. 1, 10 JULY 2003)
Indeed, a specific emphasis through
the long sweep of history on management of rainwater harvesting systems in ancient
texts, such as Rigveda (1500 BC), Atharva Veda (800 BC), Kautilya’s
Arthasastra (300 BC), Varahamihira’s Brihatsamhita (AD 550), and Kalhana’s
Rajatarangini (AD 1148–1150) may document adaptation to fluctuating climate.
There is other evidence of climate change– rainwater harvesting hypothesis. Majority
of palaces and forts (perhaps all) constructed during the 13–18th century developed
elaborate water-harvesting systems.
Addressing water problem holds the
promise in future for a world compounded by climate change, growing population and
decreasing water-impounding area of traditional tanks due to urbanization. We will
have to take into account the large-scale, natural climate variations as well as
human-induced climate change in the management of natural, social and economic systems.
Alternative to ecologically damaging, socially intrusive and capital-intensive water
management projects that fail to deliver their desired benefits, it would be useful
investing in decentralized facilities, efficient technologies and policies, and
human capital to improve overall productivity rather than to find new sources of
water supply. Such efforts would need to be encouraged with innovative policy regimes
that concurrently promote rainwater harvesting.
Monsoon is a season looked forward with great anticipation
India. Cool winds begin to blow from the southwest often with gale-like intensity,
followed soon after by welcome showers of copious rain. Skies remain cloudy for
nearly three months, the whole scene of
India gets transformed and tremendous activity is witnessed all over the country.
Sometimes, the starting of the southwesterly winds may get delayed, the quantum
of water received may get reduced and there may be long breaks in the monsoon current
causing anxiety among the people wholly dependent on this heaven-born resource.
Monsoon, therefore, is of vital concern to all of us.
During the summer months (June-September) cool winds charged with moisture blow
from the SW. Due to the existence of the high Sahya¯dri barrier across their flow
path, the low-lying moisture-rich currents are forced to rise, become cooled, condense
and precipitate in the form of rain on the windward slopes of the Sahya¯dri. The
Sahyadri has played an important role in fashioning the climate of
India and the timing of elevation of this mountain range is therefore crucial to
our understanding the periodicity and predictability of the Indian monsoon.
Similarly, the winds blowing northward over the Bay of Bengal are obstructed and
diverted westwards by the Hima¯laya causing copious amounts of rainfall all along
the foothill region and the Gangetic valley in front of the mountains. These features
point to the important role played by oceans, and the major mountain ranges of
India – the Sahya¯dri and the Hima¯laya – in the distribution of rainfall which
is characteristically Indian and termed therefore the Indian summer monsoon. (Geological
India, Selected Editorials)
|Water Harvesting in Ancient India
such systems have been integrated with agro-forestry and ethno-forestry practices,
and remain useful in contemporary conservation and ecological restoration of degraded
ecosystems. A systematic support to local innovations on rainwater harvesting could
provide substantial amounts of water.
Rural and urban water use, restoration
of streams for recreation, freshwater fisheries, and protection of natural ecosystems
are all competing for water resources earlier dedicated to food production. Under
such circumstances, decentralized rainwater harvesting adaptations prove efficient.
Traditional systems would become more efficient if scientific attempts are combined
to enhance the productivity of local knowledge. With
an insightful policy, rainwater harvesting can be promoted as a core adaptation
strategy for achieving the global security and sustainability of water resources
in an era of anthropogenic climate change.Rainwater harvesting in response to climate extremes enhances
the resilience of human society. In a world confronting local and global changes,
building resilience of human society to absorb shock, learn and develop, would depend
on sound knowledge of the historical adaptive processes that are still functional.An integrated perspective of traditional
knowledge on adaptation strategies, such as the rainwater harvesting system, is
particularly useful to comprehend vulnerability and adaptation to environmental
stresses at the local scale. I believe that neither the water policy nor the climate
policy discussions seem to notice the worth of rainwater harvesting as an adaptation
to climate change, especially in urban areas where water resources are fast depleting
due to rapid increase in population and unrestricted use of water. Studies of historical
societal adaptations to climate fluctuations provide insights into possible responses
of modern societies to future climate change and sustainable management of water
|Flooding, a common feature of
of the present SWD system in city (Mumbai) is about 70 year old, comprising of about
400 km of underground drains and laterals built on the basis of population and weather
conditions. The old SWD system is capable of handling rain intensity of 25 mm per
hour at low tide. If the rain intensity is more than 25 mm per hour and high tide
occurs, there is always a possibility of water logging.
Since the discharge of all the storm water and treated
sewage is into the
Arabian Sea, tidal variation has a major bearing in the system of storm water drainage
(SWD) resulting in flooding and water logging during heavy rains and recession of
water during low tide.
There was heavy rainfall in July 2005 when entire
City was flooded rail & road traffic was disrupted and industry suffered heavy
|Movement of Water
RUN-OFF • EVAPORATION • INFILTRATION
– along slopes draining into watercourses
– by the sun, into the atmosphere
– soaks into the soil. Available water is stored in the soil pores.