That's the question asked by the BBC in a very interesting analysis of how dependent we are on electricity for our very survival in urban areas. It looks at Venezuela's real-life experience of prolonged blackouts, and extrapolates from that to the situation in most major cities. Here's an excerpt to show you the scale of the problem.
In our modern world, almost everything, from our financial systems to our communication networks, are utterly reliant upon electricity. Other critical infrastructure like water supplies and our sewer systems rely upon electric powered pumps to keep them running. With no power, fuel pumps at petrol stations stop working, road signs, traffic lights and train systems go dead. Transport networks grind to a halt.
Our complex food supply chains quickly fall apart without computers to coordinate where produce needs to be, or the fuel to transport it or refrigeration to preserve it. Air conditioning, gas boilers and heating systems also rely upon electricity to work.
A little over 100 years ago, our cities ran on human and animal muscle power to ferry goods and waste around. Modern infrastructure is now utterly reliant upon electricity.
. . .
Putting measures in place to counter all of these potential threats is difficult and expensive ... But there are some events that cannot be planned for and the complex, interconnected nature of our electricity grids are remarkably vulnerable. Take what happened in September 2003 when a fallen tree brought down a power line in Switzerland’s Lukmanier Pass over the Alps into Italy and 24 minutes later another tree came down onto a line in the nearby Great St Bernard pass. The sudden failure of these two key lines caused other connections to Europe’s electricity network to trip, which triggered power plants across Italy to shut down. The whole of Italy was left without power because of two fallen trees starting a cascade of events.
Modern electricity grids are increasingly interconnected and complicated, making failures like this difficult to predict.
There's more at the link. Bold, underlined text is my emphasis.
There's also the sociopolitical aspect of major blackouts, of course. We've addressed that in these pages before. Remember the New York City blackout of 1977?
That was in a city where the laws and regulations effectively disarmed its citizens, preventing them from defending themselves and their property against such criminals. I'm glad I don't live there! In my part of the world, any such mob reaction would be solved very quickly by local residents, with the police required only to clean up the mess.
I highly recommend reading that BBC analysis, then planning for what you're going to do in a similar situation. You'll find some helpful hints in the series of articles on emergency preparedness linked in the sidebar; and for those who are a little more paranoid (or perhaps realistic!), you'll find lots of advice like this out there. Even in a city efficiency apartment, you should be able to store enough food and water for a week for everyone living there. That should - hopefully! - be long enough for assistance to reach you. Two weeks would be better; a month, better still. I'd also want some way of defending myself and my loved ones, and a way to fight fires, because they're likely to be started by the rabble (see the video clip above).
Remember the old acronym: PPPPPPP. Take it to heart, particularly when it comes to planning ahead for disasters. Plan what to do about such foreseeable emergencies before they happen. It might save your life.