Rainwater Harvesting- Water Conservation, Indian backdrop

Rainwater Harvesting- Water Conservation, Indian backdrop Rainwater Run off Geology, Groundwater, India Groundwater Recharge Rainwater Harvesting Methods Contact

Climate change 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.

Indian Monsoon

Monsoon is a season looked forward with great anticipation all over 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 Society of India, Selected Editorials)

Water Harvesting in Ancient India

Traditionally, 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 resources.

Flooding, a common feature of Urban calender

The core 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 losses.

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Movement of Water

RUN-OFF • EVAPORATION • INFILTRATION

Run-off – along slopes draining into watercourses

Evaporation – by the sun, into the atmosphere

Infiltration – soaks into the soil. Available water is stored in the soil pores.

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