The coastal city is the first major metropolitan area in India to deal with such an extreme water shortage, but several large cities around the world may soon face a similar crisis.

After weeks of soaring temperatures and drought, Chennai, India—the country's sixth largest city—is facing a dire water shortage. The four reservoirs that provide the majority of the city's water supply have dried up, forcing restaurants, businesses, and schools to close and leaving residents to wait in line for hours for water from municipal or private tankers.

The water crisis is hitting the region's poor particularly hard; wealthy residents can pay the premiums for water from private tankers that those living in slums can't afford.

Hundreds were arrested this week outside the municipal government's headquarters, where protesters gathered with empty water containers to blame the local authorities for mismanagement of the critical resource. The region relies on annual monsoons to replenish groundwater and reservoir supplies, but rain levels have been below average for several years, and the monsoon rains, which usually begin by June 1st, have yet to arrive. Chennai also receives some water from a desalination plant, according to Samrat Basak, the director of the World Resource Institute's Urban Water Program in India, but the plant doesn't produce enough water to supply the city's entire population.

"Only rain can save Chennai from this situation," one local official told BBC Tamil. Chennai has two monsoon seasons: One that typically stretches from June to September, and the main monsoon that begins in late October and ends in December. A good monsoon season could easily recharge the city's reservoirs, according to Basak, but the main monsoon season isn't until the fall, which means Chennai may have to secure water from neighboring states over the summer months.

Global warming is pushing the country's climate toward extremes; in 2015, massive floods, spurred by an unusually strong El Nino season, killed hundreds in Chennai and left the coastal city economically devastated.

"We are having extreme rainfall periods and then extreme dry and drought periods. During these extreme rainfall periods, we have to capture and recharge our groundwater as much as possible," Basak says. "The biggest challenge that not only Chennai, but most of India faces is very bad management of water."

India currently recycles only 15 percent of wastewater and captures less than 8 percent of rainfall—significantly less than the global averages, according to Basak. That's at least in part because of drastic urbanization. As cities expand, they've displaced wetlands and lakes that previously captured water and funneled it underground to recharge aquifers. Restoring and conserving urban water bodies could help cities in India prepare for future water shortages. Madras High Court, the high court in the state of Tamil Nadu, where Chennai is located, also criticized the state government for not taking more proactive actions to prevent the water crisis.

Smaller towns in India have run out of water before, but Chennai is the first major city in the country to grapple with so severe a water shortage. India in general is facing the worst water crisis on record, according to the National Institution for Transforming India, a government think tank, which released a report this month showing that, without drastic action, water demand in the country will exceed supply by 2030. The report found that 21 cities, including Chennai, Delhi, and Bengaluru, could run out of water as early as 2020.

"This is a situation a number of larger cities of India are facing," Basak says. "I think it's high time for the cities to look and develop their own resiliency plans to come out of such water shocks."

Water stress is increasing all over the world, as populations boom, urban development increases, and climate change intensifies. Since the 1980s, water use has climbed by roughly 1 percent a year, according to the United Nations' World Water Development Report. The 2019 report notes that four billion people already experience severe water scarcity during at least one month every year.

In 2017, Cape Town, South Africa, faced the prospect of becoming the first major city to shut off its taps after population growth and drought conditions left its reservoirs nearly too low to supply water to homes and businesses. A government campaign to raise awareness about the impending "day zero"—when the water would run dry—spurred drastic conservation efforts that, along with the arrival of much-needed winter rains, kicked the "day zero" date down the road.

The city of Chennai received its first major rainfall of the year on Thursday, though it brought little relief to the city's 4.5 million residents; it will still be many months before the reservoirs are replenished.

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