SAO PAULO, Oct 24 (Thomson Reuters Foundation) - South America's biggest and wealthiest city may run out of water by mid-November if it doesn't rain soon.
São Paulo, a Brazilian megacity of 20 million people, is suffering its worst drought in at least 80 years, with key reservoirs that supply the city dried up after an unusually dry year.
One of the causes of the crisis may be more than 2,000 kilometers away, in the growing deforested areas in the Amazon region.
"Humidity that comes from the Amazon in the form of vapor clouds - what we call 'flying rivers' - has dropped dramatically, contributing to this devastating situation we are living today," said Antonio Nobre, a leading climate scientist at INPE, Brazil's National Space Research Institute.
The changes, he said, are "all because of deforestation".
Nobre and a group of fellow scientists and meteorologists believe the lack of rain that has dried up key reservoirs in São Paulo and neighboring states in southeastern Brazil is not just the result of an aberration in weather patterns.
Instead, global warming and the deforestation of the Amazon are altering the climate in the region by drastically reducing the release of billions of liters of water by rainforest trees, they say.
The severity of the situation in recent weeks has led government leaders to finally admit Brazil's financial powerhouse is on the brink of a catastrophe.
São Paulo residents should brace for a "collapse like we've never seen before" if the drought continues, warned Vicente Andreu, president of Brazil's Water Regulatory Agency.
Dilma Pena, chief executive officer of Sabesp, the state-owned water utility that serves the city, warned last week that São Paulo only has about two weeks of drinking water supplies left.
Critics say Sunday's presidential election, which pits the governing Workers Party (PT) against the Social Democracy Party (PSDB), has led São Paulo Governor Geraldo Alckmin, of the PSDB, to delay taking action on the water crisis for fear the party would lose votes.
Already at least 14 million residents of the 44 million that live in São Paulo state have been affected by shortages as more than 35 municipalities have been forced to ration water. Even the posh Jardins neighborhood in São Paulo city is suffering, as reduced water pressure means water doesn't always make it through the pipes to the city's highest areas.
The Cantareira system, the main water reservoir feeding the region, dropped to just 3.4 percent of its capacity on Oct. 21, according to Sabesp.
Elsewhere in Brazil's southeastern region, key crops such as coffee, sugarcane and oranges, some of the country's top exports, are expected to be severely hurt this year.
Sugarcane production will be at least 15 percent lower, according to Unica, Brazil's sugarcane industry association.
Dry conditions have delayed planting of the 2014-2015 soybean crop, threatening Brazil's goal to reach an output record for a third straight year.
Ironically, soybean production, as well as cattle ranching and logging, are responsible to a great deal of Amazon deforestation, scientists say.
Deforestation jumped by 29 percent in the last officially recorded period, between August 2012 and July 2013, marking the first increase since 2008.
A survey produced by INPE using satellite imaging showed that the Amazon lost 5,891 square kilometers, or 2,275 square miles, of forests in that period, an area almost five times the size of the city of New York.
With fewer trees, the Amazon's capacity to work as a water pump, absorbing moisture from the Atlantic Ocean and releasing millions of liters of humidity into the air, is being reduced, scientists say.
Brazilian meteorologist José Marengo, who has contributed to Intergovernmental Panel on Climate Change reports, coined the term "flying rivers" in the 1990s to describe air currents that carry water vapor - rising from the Amazon and blocked to the west by the Andes mountains - to central and southeast Brazil and all the way to northern Argentina.
About 20 billion tonnes of vapour evaporate from the Amazon region every day. A big Amazonian tree, with a crown measuring 20 meters, can evaporate up to 300 liters a day, compared with one liter evaporated by a square meter of ocean, according to Nobre.
In January and February this year, when rain is usually abundant in central and southern Brazil, the flying rivers failed to flow south, according to data from INPE's Center for Weather Forecasts and Climate Research.
"What's happening now highlights the importance of preserving and replenishing the Amazon if we want to prevent São Paulo from becoming a desert," Nobre said. (Reporting By Adriana Brasileiro; Editing by Laurie Goering)