I'm from Chennai, and was caught in the Dec 2015 floods at Defence Colony. Luckily, I was in a 2-storey house with a covered 3rd-floor landing as well, and we were able to move documents and minimal utensils and edibles quickly to the higher floors. Eventually, 6 people in total remained on the first floor until the Adyar river water receded after 36 hours, and we slept and remained there for almost 2 weeks. Almost everything downstairs, in the garage and two vehicles were fully immersed above roof level. Some lessons from this event:
1. Keep all your critical documents, bank passbooks, share certificates, computers, etc. safely upstairs. It will help you recover quicker after a disaster if your documents are intact. Otherwise, it takes *years* of work to get replacement documents. You can easily replace furniture, appliances, clothes and so on, but original documents are indispensable to get your life back in order.
2. Keep one bubble-top can of drinking water upstairs, along with dry edibles like biscuits and so on, the moment there is heavy rainfall and the likelihood of flooding. Even better to have one kerosene or gas stove upstairs for use in an emergency.
3. Have a rain-water harvesting setup on the top floor - it was a life saver for us. All the other sources of water were contaminated, and the tubewell was also flooded and contaminated. However, a roof on the top floor had an overflow pipe that allowed us to collect maybe several hundred litres of water whenever it rained over the next few weeks, and that water is potable in an emergency. If you have Chlorine tablets (Isocyanuric Acid) tablets, you can add one to a bucket of water to chlorinate it and drink it. Keep chlorine tablets safely away for use in an emergency - Chennai Corporation distributed a small quantity to residents after about 48 hours, but it's better to have a few in hand at all times.
4. if you have the time, disconnect the battery cables of vehicles the moment waters start entering the compound. A vehicle with a disconnected battery can be repaired with a bit of effort. If the battery remains connected, a lot of the electronic modules will be destroyed by electrolysis, and the repair costs will be prohibitive. The more the electronics, the lower the chance of a repair. One Ertiga was totaled, but a 2003 Wagon R was successfully repaired with the help of an expert independent Maruti mechanic. Cheap, simple cars can be repaired after a flooding, but expensive cars will likely be total losses.
5. Keep one LED lamp and one feature phone with a long battery life for emergencies. Smartphones will be dead within 12 hours due to dead batteries, but an old SMS-capable feature phone can retain battery life for a week or longer. I managed to keep my Nokia X2-01 going for about 9 days by switching it on and off, and using it mainly for sending/receiving SMSes (both for ourselves, and for marooned neighbours without working phones). We were lucky that there was one BSNL cell tower on high ground that remained operational throughout the flooding.
The long-term lessons are simple, but people will forget it quickly, within a few months: don't build residential habitations on flood plains of rivers, however small they may appear to be. Flood plains are often 10s of km in width - the Adyar river is normally about 100m wide, but its flood plain extends from Arumbakkam to Guindy National Forest, and includes almost all of Central Chennai. Every square inch has been built on over the last 80+ years without any regard for the possibility of extreme flooding. Floods are natural and cyclical, but flooding disasters like Chennai and Kerala are 100% man-made.
