The London Riots (also other Cities in England) were essentially quite predictable. The spark that lit the touch paper to kick off the riots wasn't predictable at all. The UK government was essentially caught of guard (many were vacationing in the south of France and Caribbean) by the way the riots grew and expanded to other areas through Internet social media communications and even by the normally law abiding people that ended up getting involved in the looting and criminality. But I suspect that the USA is quite a different to England due to the fire arms situation and the risk to life being involved in an actual Riot.

The US Federal Government internal security agencies within the USA has some very effective intelligence gathering networks and its recent ammunition purchases indicate that they are possibly preparing for a very serious potential situation on a scale previously unknown.

For example the electronic Food rationing system (administered by a well known Wall Street Banking Firm), which have almost 1/6 of the countries population dependent in the US could be subject to systemic economic failure. Even if this hand to mouth system was recoverable even after a week or two, this could be too late.

I really wouldn't dismiss this as not being a serious issue requiring at least some preparation planning out of hand.