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King tide is a popular term used to refer to an especially high tide. ‘King tide’ is not a scientific term, nor is it used in a scientific context. Use of the term ‘king tide’ originated in Australia, New Zealand and other Pacific nations to refer to an especially high tide that occurs only a few times per year. The term has now come to be used in British Columbia and the United States as well.
King tides are simply the very highest tides. Conversely, the low tides that occur at this time are the very lowest tides. They are naturally occurring, predictable events. Tides are actually the movement of water across the Earth’s surface caused by the combined effects of the gravitational forces exerted by the moon and the sun and the rotation of the earth which manifest in the local rise and fall of sea levels. Tides are driven by the relative positions of the earth, moon, and sun, the elliptical orbits of the celestial bodies, land formations, and relative location on the earth. In the lunar month, the highest tides occur roughly every 14 days, at the new and full moons, when the gravitational pull of the moon and the sun are in alignment. These highest tides in the lunar cycle are called spring tides.
The proximity of the moon in relation to the earth and the earth in relation to the sun also has an effect on tidal ranges. The moon moves around the earth in an elliptical orbit that takes about 29 days to complete. The gravitational force is greatest when the moon is closest to the earth (perigee) and least when it is farthest from the earth (apogee – about two weeks after perigee). The moon has a larger effect on the tides than the sun but the sun’s position also has an influence on the tides. The earth moves around the sun in an elliptical orbit that takes a little over 365 days to complete. Its gravitational force is greatest when the earth is closest to the sun (perihelion – early January) and least when the sun is farthest from earth (aphelion – early July).
The king tides occur when the earth, moon and sun are aligned at perigee and perihelion, resulting in the largest tidal range seen over the course of a year. Alignments that are ‘near enough’ occur during approximately three months each winter and again for three months in the summer. During these months, the high tides are higher than the average highest tides for three or four days. The predicted heights of a king tide can be further augmented by local weather patterns and ocean conditions. Winter king tides may be amplified by winter weather making these events more dramatic. In the northern hemisphere, the term king tide is used to describe each of these winter high tide events. On Australia's East Coast, the highest of each of these periods (i.e., one in winter and one in summer, totaling two per year) are known as the king tides. In this region of the world, the winter king tide usually occurs at night and therefore goes unnoticed. Consequently the summer king tide usually catches the most attention.
Photo initiative 
The King Tide Photo Initiative educates people about the potential effects of rising sea levels due to climate change. During this initiative, organizations reach out to the general public to photograph local areas inundated by king tides and then encourage them to post the photos online for others to see. These photos can help people visualize the way sea level rise may affect our communities in the future. The photos generate information that can be used by coastal communities to inform people about the anticipated effects of sea level rise and perhaps lead to policy change and local adaptation.
King tides are a natural part of the tidal cycle and are not a result of climate change but they do provide a view of the locally highest tides, which may occur more frequently as sea levels rise due to the effects of climate change.
The initial event was conducted by the NSW Department of Environment, Climate Change and Water and run throughout NSW on the east coast of Australia during the king tide on 12 January 2009. King Tide Photo Events in North America are modelled on this initial event and a similar event conducted by British Columbia’s LiveSmart BC campaign.
See also 
- "A snapshot of future sea levels: photographing the king tide". NSW Government, Office of Office of Environment and Heritage. Retrieved 7 Sep. 2012. Unknown parameter
- "California King Tides Initiative". Retrieved 7 Sep. 2012.
- "King Tides in Washington State". State of Washington, Department of Ecology. Retrieved 7 Sep. 2012.
- "BC King Tide Photo Initiative". LiveSmart BC. Retrieved 7 Sep. 2012.
- King tides photo initiative - British Columbia, Canada
- King tides photo initiative - Washington State, USA
- King tides photo initiative - Oregon, USA
- King tides photo initiative - California, USA
- King tides photo initiative - Long Island Sound, USA
- King tides photo initiative - Barnegat Bay, USA
- King tides photo initiative - Australia
- King tides photo initiative - New South Wales, Australia
- King Tide | The Sinking of Tuvalu