You would not generally associate Chennai, the capital of Tamil Nadu, with floods. A bustling metropolitan that is home to more than 7 million people, it faces water shortages year after year. However, in November 2015, a cyclonic weather cycle began to affect the state, with the city receiving 1,049 mm (41.3 in) of rain in that month alone, the highest since November 1918, when 1,088 mm (42.8 in) of rainfall had been recorded. The Chennai International Airport recorded 266 mm of rainfall in 24 hours on 15 November. By 17 November, much of the city had flooded, even though the rains had stopped.

The rains brought Chennai to a standstill. Schools, colleges and offices were closed for the most part, while lakes that had been absolutely dry for more than two decades breached their banks, leading to submerging surrounding areas. Water rose up to the second floor in some localities, with intermittent power cuts and limited mobile connectivity across the city.

And then came the 1 December deluge. On that fateful day, in just a span of 12 hours, Chennai received a record- breaking 272 mm of rainfall. By 8 December, Chennai had recorded 539 mm of rain, as opposed to the monthly average of 191 mm. The incessant rain put pressure on the already overburdened drains and, by the afternoon of 1 December, power supplies had been suspended to 60 per cent, while several city hospitals had stopped functioning. For the first time since its inception in 1878, The Hindu did not publish a print edition on 2 December as workers were unable to reach the press. The Southern Railways cancelled all major train services and the Chennai International Airport was closed until 6 December. Chennai was officially declared a disaster area on the evening of 2 December.

It was in this crisis that individuals mobilised on social media like never before.

Mobile connectivity was not as damaged as other information services, and social media, accessed on smartphones, became the number one source of information during the crisis. Having a fully charged mobile phone became such a critical asset that, along with food, water and other relief materials, power banks were distributed to allow people to charge their phones.

Several emergency numbers had been set up, but getting through to those numbers was difficult. The veracity of the numbers also became an issue. As a result, Twitter and Facebook became the “go-to” places for everything related to rescue efforts, from keeping track of the worst-affected areas and their requirements, to putting out SOS calls or volunteering for help.

Facebook activated its “safety check” feature – which allowed users to mark themselves as “safe” on their profile during a crisis – while several Facebook groups like Chennai Rain Relief provided basic tips on how to rescue people and lists of dos and don’ts, apart from coordinating rescue efforts. Facebook also became a hub for those who were trying to contact their families.

One ingenious resource that was circulated widely during the floods was a crowdsourced effort that mapped inundated roads in the city. Over 2,500 flooded roads were added to the city’s map via social media, which was put together by engineer and information designer, Arun Ganesh.

The Chennai floods were a superb example of the power of collective effort. Users across social media channels came together to offer shelter, food, transport, and even a place for people to charge their phones. SOS messages asking ground teams to rescue stranded family members also went back and forth, and there were many who offered their homes and offices to those who were stranded.

Perhaps the most simple yet effective tool during the floods was the website

It began as a simple Google spreadsheet. Sowmya Rao was trying to help her uncle and aunt figure out whether it was safe to stay in their house in suburban Chennai or move to a friend’s place. When she found out that the area they lived in was under severe risk of flooding, she relayed the message to them. But she felt helpless about the countless others who were facing the same plight as her relatives. Acting on a suggestion by another Twitter user, she created the Google spreadsheet that went on to become the website

The idea was simple: crowdsource details about those who could offer shelter, and pass it on to those who were tweeting about rising waters. A hastily put-together spreadsheet soon blossomed into a multi-faceted, volunteer-driven, highly energetic online movement to help Chennai, and ended up being used by the general public, police officers, government officials and celebrities alike.

Rao later wrote in a blog on Twitter India that the entire operation was run “almost exclusively on Twitter”.

To segregate pleas for help from updates on rain and volunteering efforts, users attributed tweets to one of the three hashtags: #ChennaiRainsHelp, #ChennaiRescue, and #ChennaiVolunteer to systematically organise all incoming tweets. Twitter was also active in ensuring that this information reached as many people as possible by promoting it on its official India page.

Karthik Balakrishnan, the web developer behind, told an English daily that he got the idea to make the website after he privately messaged Sandhya Ramesh, another Twitter user who was actively coordinating relief efforts on Twitter at the time. She, in turn, linked him to Sowmya Rao’s Google spreadsheet. Balakrishnan and Rao discussed turning the spreadsheet into a website at 2 am on 2 December, following which Balakrishnan booked the domain and posted the site by 3.30 am.

Raheel Khursheed, head of news, politics and government, Twitter India and South East Asia, says, “Twitter is the first port of call for people responding to a disaster as we’re a live, real-time public platform. The advantages are manifold. You can have conversations around organising relief at scale, you can form groups quickly, you can group DM with 10 or 15 people and start a conversation around coordinating relief efforts.”

Twitter tied up with all the volunteer groups who were working together on the #ChennaiRainsHelp campaign ­ including InCrisisRelief, The News Minute, Airtel, Zomato, Goonj, Bhumi, Uday Foundation and Practo – with data support from Delhi-based SocialCops. “The partners we were working with were responding to the disaster in their own way, so we thought it may be a good idea to just get everyone onto the same page, and help them with data,” Khursheed says.

By 5 December, the team began facing a new issue. They had data from the beginning of the floods, but did not know how many of those who had requested help still needed it. With Exotel, a cloud telephony provider, developed an SMS system which sent out messages to the listed numbers. Balakrishnan told a website, “The SMS basically said you have three numbers here. If you still needed help with food and aid, please give a missed call on one number. If you were safe, give a missed call on another number, and if you were in urgent need of help, a third number was given. All this data was tied into our database, and we coordinated people to drive relief efforts accordingly.”

A volunteer team of at least 50-60 people kept track of everything online, manually matching relief efforts on a rotation basis 24 hours a day.

It required knowledge of the city and the language: Tamil. Getting a location from a plain text address to marking it on Google Maps also required manual effort.

“For about 75 to 80 percent of the areas, the team was able to get the latitude-longitude coordinates on a map by searching on Google’s Location API. For the [remaining] 20 percent, where the landmarks were vague, the team coordinated over phone calls. On average, each person of the now 200-member team made about 200 to 250 phone calls over a period of four days. The phone calls were made to coordinate with people on the ground, to verify and find out if people had gotten any assistance,” Balakrishnan said.

Rao says in her blog post, “In less than 7 days, the crowd- sourcing effort taught many of us the importance of efficient coordination as well as [the] veracity and authenticity of data. The biggest advantage of using Twitter and other online media here was real-time data relaying. People on the ground got to know updates from other areas almost instantaneously thanks to tweets. This enabled efficient volunteer coordination, not only on the field, but also with outstation supplies and distribution. This was a great demonstration of how information is truly powerful.”

Excerpted with permission from India Social: How Social Media Is Leading The Charge And Changing The Country, Ankit Lal, Hachette India.