São Paulo, in southeast Brazil, is the largest city in South America and the 7th largest metropolitan region in the world, with more than 21 million people. It's the engine behind Brazil's richest state, which is responsible for one-third of the country's GDP.

And right now, the region is running dangerously low on water, thanks to the worst drought in eight decades.

officials are warning the region could face 'collapse' if the drought continues

São Paulo's reservoirs have dwindled to less than 5 percent of their original capacity, 13 million people are facing water outages, and officials are warning that the area could face "collapse" if it doesn't rain soon — with businesses and households struggling to find fresh water.

NASA's Earth Observatory recently posted satellite photos showing just how dire the situation has gotten. Water levels in the Jaguari Reservoir — one of five reservoirs that supplies water to some 10 million people — have plummeted between 2013 and 2014. The slider tool below helps you see the change:

São Paulo's Jaguari Reservoir in 2013 (left) and 2014 (right)

"The drought began last austral summer (December to February), when São Paulo state received about one-third to half of its usual amount of rain during what should have been its wettest season," NASA says. "In the seven months since, rainfall has been about 40 percent of normal." Some scientists have blamed the drought on the lack of vapor clouds from the Amazon that usually carry rain to south and central Brazil. (The problem, they say, may be exacerbated by deforestation and global warming.)

At least 60% of residents have now had their water cut — some for more than 6 hours

The water shortages are starting to cause severe disruptions. According to Bloomberg, 60 percent of São Paulo's residents have now reported that they've had their water cut at least once in the last 30 days — with many of the outages lasting more than 6 hours.

The region's economy is also taking a hit. The Wall Street Journal reports that coffee and sugarcane harvests are withering, while manufacturers are struggling to find cooling water and one major meat-packing plant has had to shut down temporarily. (Indeed, the drought in southeastern Brazil is one big reason why global coffee prices are expected to rise in the future.)

"If the drought continues, residents will face more dramatic water shortages in the short term," said Vicente Andreu, president of Brazil’s National Water Agency, according to Weather.com. "If it doesn’t rain, we run the risk that the region will have a collapse like we’ve never seen before."

If the drought continues, officials have warned, states across Brazil may have to resort to energy rationing — since there won't be enough water to feed the hydroelectric plants that provide most of the nation's electricity.

Did São Paulo mismanage its water supplies?

São Paulo's woes have also become a major issue in Brazil's presidential campaign, which is holding a final run-off on Sunday, October 26. Current President Dilma Rousseff has criticized the region's handling of water issues — her challenger, Aecio Neves, hails from the party that governs the region.*

Among other things, critics charge that São Paulo failed to institute conservation measures until it was much too late — possibly out of fear of angering voters. Two months ago, the region's state-run water utility Sabesp declined to implement water-rationing measures despite orders from federal officials. Water managers insisted that smaller measures — like offering discounts to people who cut their water use or redirecting water from surrounding reservoirs — would suffice.

And experts warn that few of Brazil's cities are ready to deal with future water shortages. "It is now clear that our policies on management of water resources are unsustainable," climate scientist Marcos Heil Costa told NASA. "No city in southeast Brazil seems prepared to handle a drought like this one. It is a mix of a lack of preparation for low levels of rain and a lack of environmental education in the population. Most people continue to use water as if we were in a normal year."

* Correction: Aecio Neves hails from the party that governs São Paulo state, but he is not from the state himself.

Further reading

This piece from Jan Rocha of the Climate News Network offers more on the science behind Brazil's wicked drought.

A recent brief from the Center for Climate and Security explained why Brazil may continue to suffer water woes as the population grows and global warming advances. By one estimate, 73 percent of the country could face water shortages in the coming decade.

Deforestation in Brazil is surging again — after years of decline.

Why you're going to be paying more for coffee soon. (Drought in Brazil is one reason.)