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One theory about why the population of Easter Island plunged around the turn of the 18th century is that islanders ran out of timber.
Anthropologists suggest they decimated their forests which, in turn, wreaked havoc on the island's ecosystem. With less food available and a narrower diet, Easter Island's population shrank.
Another is that stowaway rats arrived in canoes and destroyed vegetation, and that islanders had to eat the animals as a source of protein. Yet another is that visiting European sailors introduced disease.
Take your pick.
The first two theories suggest that we as a species can adjust to unfavorable conditions, albeit, in the case of Easter Island, not without huge effects on population levels. The first theory also implies humans are not the sharpest of tools in the box.
But we would be the bluntest of chisels if we didn't learn from past experiences.
And that is what the drought-stricken urban area of São Paulo must do. It is irrelevant whether its main reservoir system, Cantareira, operated by utility Sabesp, fully recovers. It is at around 20% of capacity, including emergency reserves, compared with around 60% two years ago. And we cannot predict when, or if, it will return to similar healthy-ish levels.
What lawmakers must do is consider the current situation as the new normal.
Money is being spent on infrastructure to bring in water from other parts of the region and reduce leakage, but sucking more water from rivers and mending pipes is not the panacea for São Paulo's water woes. It's just part of the solution – especially as demand is likely to keep increasing and climate patterns appear to be changing. The International Panel on Climate Change said that under the IS92a CO2 emissions scenario, a "business-as-usual" type scenario, there could be a high risk of summer droughts in south-central Brazil.
According to the IMF's latest economic forecast, Brazil's GDP will contract 1% this year but will expand 1% in 2016 and slowly pick up pace. The fund predicts that the country will register GDP growth of 2.5% in 2020. And as the nation's economic engine stops sputtering, the population growth rate of industrial urban areas such as São Paulo, home to around 20mn, will probably move up a gear. Indeed, by 2025 the population will have increased by an estimated 5mn.
Along with greater prosperity comes greater demand for water. To secure supplies for generations to come, steps must be taken.
Contributors to a debate in the New York Times offer suggestions about what water-hungry California – also suffering from a crippling drought – can do in the short and long-term to tackle water scarcity.
Among the proposed remedies are some that could work in Brazil. NYT contributor Heather Cooley, director of the Pacific Institute's Water Program, suggests adopting water prices and pricing structures that effectively communicate the value of water, modernizing monitoring systems, expanding education and outreach efforts and promoting the adoption of efficient technologies and practices.
What everything boils down to is that the bitter pill that needs to be swallowed is innovation and conservation. This needs to be achieved in a way that has the least impact on consumers and industry.
But action needs to be taken and politically tough decisions made and stuck to. Cantareira reached critically low levels in February – this cannot happen again.
Federal and state lawmakers have got a mountain to climb but climb it they must to make sure the São Paulo urban area, a key engine room of the Brazilian economy, does not seize up decades down the road and leave industry and householders high and dry.