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Lessons from São Paulo’s Water Shortage

March 17, 2015

Jaguari Reservoir, one of five in São Paulo’s Cantareira System, which is at about 13 percent of capacity. Image acquired on February 11, 2015. Image Credit: NASA Earth Observatory.

Jaguari Reservoir, one of five in São Paulo’s Cantareira System, which is at about 13 percent of capacity. Image acquired on February 11, 2015. Image Credit: NASA Earth Observatory.

It’s getting harder and harder to separate nature’s role in disasters from our own, and the dire water predicament confronting São Paulo, Brazil, is no exception.

But as with the ongoing drought in California, there are important lessons from São Paulo’s grim situation that can help us prepare for the “new normal” that’s unfolding.

It’s indisputable that São Paulo, the economic heartbeat of Brazil, is in trouble. The megacity of 20 million people is suffering its worst drought in eight decades. The five reservoirs in the Cantareira system, which provides nearly half the city’s drinking water, are at a dangerously low 13 percent of capacity. That’s up from even lower levels thanks to some recent rains, and while more precipitation could arrive in the coming weeks, historically the driest period of the year is April through September, just around the corner.

Some São Paulo residents have gone without tap water for days at a time. Others have fled the city, creating a new brand of “water refugees.”

As Brazil gears up to host the 2016 summer Olympics, businesses are suffering from the lack of water. Economists say the drought could shave 2% off of Brazil’s GDP.

Meanwhile, a “clandestine drilling fever” is taking place across the city, according to an NPR report. As people and businesses worry about rationing, they are drilling their own wells to access groundwater. This unregulated, wildcat drilling threatens to pollute underground supplies, worsening the drought’s long-term impact and raising public health risks.

Unlike Los Angeles, São Paulo is not a desert city. Whereas LA averages just 15 inches (381 millimeters) of rain a year, São Paulo averages 57.3 inches (1455 mm). With more than 12% of the world’s renewable freshwater, Brazil is sometimes called the “Saudi Arabia of water.”

So what’s going on, and what can we learn from São Paulo’s dire situation?

Land Use and Climate Links to Water Supply

First, although droughts are a natural phenomenon, their origin and consequences can be influenced by human actions. Land use, for example, greatly impacts how water moves and cycles through a watershed.   In the case of São Paulo and southeastern Brazil, the long-term deforestation of the Amazon rainforest may have played a significant part in the origin of the drought.

It’s been known for three decades that the forests of the Amazon recycle about half of the precipitation that falls in the basin. Easterly winds bring moisture inland from the Altantic coast, and then evapotranspiration from the forest vegetation re-circulates that moisture westward until it meets the high-elevation Andes.

Although the rate of Amazon deforestation has slowed considerably*, some 224,000 square miles of forest– an area nearly one-and-a-half times the size of California – have been cleared since 1980.

In a 1984 article published in the journal Science, researchers Eneas Salati and Peter Vose of the University of São Paulo describe this “unique precipitation and water recycling regime” and warned of the dangers of massive tree-cutting.

“Continued large-scale deforestation,” the scientists wrote, “is likely to lead to increased erosion and water runoff with initial flooding in the lower Amazon, together with reduced evapotranspiration and ultimately reduced precipitation.”

Indeed, while São Paulo has been gripped by drought, the Bolivian Amazon has experienced massive flooding. Besides deforestation, another cause of these two extremes has been a high-pressure atmospheric “block” that has shunted rainfall back through the lower Amazon and away from São Paulo and the southeastern portion of the country.

This Brazilian anomaly is not unlike the high-pressure “ridge” off the U.S. Pacific Coast that blocked rains from falling in California, exacerbating the drought there. Researchers at Stanford University found that the formation of this atmospheric ridge is “very likely” linked to human-caused climate change.

Building a Resilient Water System

Slowing both Amazonian deforestation and global greenhouse gas emissions might help prevent the number or severity of future droughts in southeastern Brazil.

But the most important take-away lesson for São Paulo is that the future is unlikely to look like the past, and so it should work now to create a more resilient water system.

More than 30 percent of São Paulo’s drinking water is estimated to be lost to leaks in the distribution network or to outright theft. Those are costly losses at any time, but especially during a severe drought. Finding and repairing leaks is a cost-effective conservation measure that could be implemented now to shore up the water system.

Second, the city should not only regulate well drilling, but plan strategically for conjunctive use and management of its surface and underground supplies. Groundwater reserves can be life-savers in times of drought, as long as the volumes pumped and used during dry years is replenished during wet ones.

Third, if extreme droughts are more likely in the future, city water managers need to adjust their risk formulas and take action sooner to avoid catastrophic outcomes. That means declaring drought emergencies and instituting restrictions on water use (for example, on landscape irrigation) earlier than done in the past. The possible human and economic consequences are just too great to allow reservoir levels to get so low before issuing restrictions on discretionary water uses.

And fourth, São Paulo could benefit from investments in stormwater capture and wastewater recycling to boost local water supplies. Along with conservation, such measures can help meet water demands without the need for costly long-distance water transfers. Los Angeles, for example, has set a goal of halving its reliance on imported water within a decade by implementing measures such as these.

Meanwhile, the drumbeat of drought goes on in South America’s largest city. It may take some Olympian feats to escape the water predicament in which it now finds itself.


*Three days after posting this piece I came across an interview with Philip Fearnside, a leading authority on Amazonian deforestation, in Yale Environment 360, who said that deforestation in the Amazon has surged in the last six months, with the period September 2014 to January 2015  showing forest clearing rates more than  double the same period a year earlier.