What are king tides?

It's that time of the year again for the South Coast,where winter storm surges and kingtides can lead to flooding for low-lying coastal areas.

King tideis a colloquial term for the highest tides. These kinds of tides happen due to extra gravitational forces on Earth's oceans that are produced by specific alignments of the sun and the moon.

• PHOTOS:Vancouver getting out the sandbags to help fight winter flooding

Every two weeks, the moonand the sun align on the same side of our planet toproduce gravitational forces onEarth that result in tides that are about 20 per centhigher than normal.This isknown asa springtide (although it has nothing to do with the season).

About three or four times a year, the moon will be at its closest approach to Earth on its elliptical orbit. This is called a perigean tide.

If these two astronomical events line up,then you get a perigean spring tide otherwise known as aking tide. In this situation, the sun and the moon line up on the same side of Earth,and the moon is also at its closest approach to Earth.

This usually happens around late December or early January, atime when Vancouver also gets storms. When you factor in a storm surge, which is the rising waters that comes with low-pressure systems, plusthe forward push of water thanks to the winds around the low-pressure systems that's a lot of extra water.

And that's why there is so much concern whena winter storm lines up with King tides.While the king tides can be calculated ahead of time,predicting winter storms much farther out than a week is a different story.

Global warming will continue to mean rising sea levels and a future for B.C. that will include more extreme weather events. All the more reason for the South Coast to start preparing for bigger annual floods.