On top of this, there is the related question of climate change. Most researchers are extremely reluctant to attribute any single weather event to global warming.
But Dr Peter Stott, a leading climate scientist at the UK Met Office, says that since the 1970s the amount of moisture in the atmosphere over the oceans has risen by 4%, a potentially important factor.
That does not sound like much but it does mean that extreme rain storms may bring more rain than before - with more moisture in the air, what goes up must come down, and the odds are worse.
"That could make the difference between a place getting flooded or not getting flooded," he said.