Houston expected to get 17 times more rain than fell on Calgary during the 2013 flood

As Tropical Storm Harvey continuedto pound southeastern Texas on Monday, the U.S. National Weather Service issued an ominous forecast.

Some parts of Houston are now expected to receive an almost inconceivable 1.3 metres of rain, in total, by the time the storm finally blows through.

• 'I'm not complaining, we're alive': Houston battling Harvey but much more rain to come

To put that in perspective: It's nearly 17times the amount of rainthat fell on Calgary over a period of three days during the June 2013 flood.

It's not an apples-to-apples comparison, though, as Calgary's flooding was amplified by even heavier rainfall and snowmeltin the mountains upstream that accumulated andcarried a surge of high water down the Bow and Elbow rivers.

In the Canmore area, more than 200 millimetres fell over a 48-hour period, and much of that precipitation rapidly made its way downstream to Calgary, about 100 kilometres to the east.

Compare that to the 1,270 millimetres ofrain that Harvey is expected to dump on Houston, and you can seehow quickly cars and trucks were replaced by boats and rafts on the Texas city's streets.

That's more rain than Houston normally receives in an entire year, and it would be the largest amount of rainfall ever recorded in Texas froma single storm.

"The breadth and intensity of this rainfall is beyond anything experienced before," the National Weather Service said in a statement.

BrockLong, the director of the Federal Emergency Management Agency, predicted the aftermath of the storm would require FEMA's involvement for years.

"This disaster's going to be a landmark event," Long said.

• MORE FLOOD NEWS |Alberta floods: before and after photos
• MORE FLOOD NEWS |How Calgary has prepared for the next big flood since 2013's disaster