"India receives most of its rainfall in just 100 hours out of 8760 hours in a year. If this water is not captured or stored, their will be no water for the rest of the year"
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| Picture By Edal Anton Lefterov (Own work)via Wikimedia Commons |
Just the simple richness of rainwater availability that few of us realise because of the speed with which water, the world’s most fluid substance, disappears. Imagine you had a hectare of land in Barmer, one of India’s driest places, and you received 100 mm of water in the year, common even for this area. That means that you received as much as one million litres of water — enough to meet drinking and cooking water needs of 182 people at a liberal 15 litres per day. Even if you are not able to capture all that water — this would depend on the nature of rainfall events and type of runoff surface, among other factors — you could still, even with rudimentary technology, capture at least half a million litres a year.
It is, in fact, only with this rudimentary technology that people came to inhabit the Thar desert and have made it the most densely populated desert in the world. And assuming you could capture the 2000 mm annual rainfall that is common in eastern India, you would need only 500 square metre of land (a 21 metre by 21 metre plot) to capture one million litres. It is also interesting to note that rural population density follows intensity of annual rainfall. Barmer, for instance, has less rainfall but few people and a lot of land available per person whereas 24-Parganas in West Bengal has much more rain but more people and less land available per person.
Even in the villages suffering from drought this year, it is not as if there was no rain. But the people let the water go. It does not matter how much rain you get, if you don’t capture it you can still be short of water. It is unbelievable but it is true that Cherrapunji which gets 11,000 mm annual rainfall, still suffers from serious drinking water shortages.
In fact, we have consistently argued that there is no village in India that cannot meet its basic drinking and cooking needs through rainwater harvesting. Figures speak for themselves. India’s average annual rainfall is 1170 mm. It varies from 100 mm in the deserts of Western India to 15,000 mm in the high rainfall hills of the Northeast. Nearly 12 per cent of the country receives an average rainfall of less than 610 mm per annum while 8 per cent receives more than 2500 mm. But more than 50 per cent of this rain falls in about 15 days and less than 100 hours out of a total of 8760 hours in a year. The total number of rainy days can range from a low of five days in a year in the desert regions of Gujarat and Rajasthan — though on some of these days there can be high-intensity rainstorms — to 150 days in the Northeast. Therefore, it is very important to capture this rainwater which just comes and goes in a few hours.
Recognising this fact that almost all the rain comes down in a few years, our ancestors had learnt to harvest water in a variety of ways:
(a) They harvested the rain drop directly. From rooftops, they collected water and stored it in tankas built in their courtyards. From open community lands, they collected the rain and stored it in artificial wells.
(b) They harvested monsoon runoff by capturing water from swollen streams during the monsoon season and stored it in zings in Ladakh, ahars in Bihar, johads in Rajasthan and eris in Tamil Nadu, to name a few.
(c) They harvested water from flooded rivers in places like north Bihar and West Bengal.
The strategy for drought proofing would be to ensure that every village captures all the runoff resulting from the rain falling over its entire land and the associated government revenue and forest lands, especially during years when the rain was normal, and store it in tanks or ponds or use it to recharge the depleting groundwater. It would then have enough water in its tanks or in its wells to cultivate substantial lands with water-saving crops like millets and maize.
source:downtoearth.org
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