King Tide – What It Is and When It Occurs

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King Tide

A king tide is a non-scientific term that describes the highest high tides that occur along coastlines. These extreme tides cause unusually high water levels, often leading to coastal flooding, erosion, and other environmental impacts. While the term “king tide” is popular in the media and among the public, it does not have a precise scientific definition. Instead, it refers to the natural peak in the tidal cycle when the sun and moon’s gravitational forces align most strongly.

  • King tides are the highest tides of the year, typically occurring twice a year.
  • King tides occur at a new moon or full moon (supermoon) when the Moon is at its closest approach to Earth (lunar perigee).
  • The proximity of the Moon plays the biggest role in determining when a king tide occurs, but the winter king tide tends to be bigger because the Earth is closer to the Sun (perihelion).

Why Is It Called a King Tide?

The term “king tide” describes the “king” or the most prominent of tides, indicating the highest of the high tides. The word “king” emphasizes the tide’s magnitude and the significant impact it can have on coastal regions. The use of “king” also conveys the idea of something that reigns supreme, much like how these tides dominate over all others in height and intensity.

What Causes a King Tide?

King tides result from the combined gravitational forces of the moon and the sun on Earth’s oceans. While regular tides are the result of these gravitational interactions, king tides occur when the alignment and proximity of the moon and sun to Earth amplify these effects.

The main factors contributing to king tides include:

  1. Lunar Perigee: This is the point in the moon’s elliptical orbit when it is closest to Earth. During perigee, the moon’s gravitational pull on Earth’s oceans is stronger, leading to higher tides.
  2. Solar Perigee (Perihelion): This is the point in Earth’s orbit when it is closest to the sun, typically occurring in early January. The sun’s gravitational pull is stronger during this time, contributing to higher tides.
  3. Syzygy: This term refers to the alignment of the Earth, moon, and sun. Syzygy occurs during new moons and full moons when the gravitational forces of the moon and sun combine to produce the highest tides, known as spring tides. King tides are extreme spring tides that occur when syzygy coincides with the lunar and solar perigees.

Conditions That Produce a King Tide

King tides occur when several specific conditions align:

  • Full or New Moon: King tides usually occur during full or new moons, when the gravitational forces of the moon and sun work together to create higher tides.
  • Lunar Perigee: If a full or new moon coincides with the moon being at its closest point to Earth, the tide is even higher.
  • Solar Perigee: When Earth is closest to the sun, the sun’s gravitational effect on the tides is at its peak, further increasing tide levels.
  • Local Topography and Weather: Local coastal features, weather patterns, and ocean currents also influence the height of king tides. Storm surges, strong winds, and atmospheric pressure exacerbate king tides, leading to more severe coastal flooding.

King Tide vs Spring Tide

All king tides are spring tides, but not all spring tides are king tides. King tides are the most extreme version of spring tides, occurring when additional factors such as the moon’s perigee and Earth’s perihelion combine to create the highest possible tide levels:

Spring Tide:

  • Definition: A spring tide or syzygy tide occurs when the sun, moon, and Earth align during a full or new moon, which happens approximately twice a month. The term is not connected with the spring season, but instead relates to “springing forth” like a water spring or artesian well. The alignment of the sun, moon, and Earth amplifies the gravitational forces exerted on Earth’s oceans, leading to higher high tides and lower low tides than usual.
  • Frequency: Spring tides occur twice a month, during every full and new moon.
  • Magnitude: While spring tides are higher than normal, they are part of the regular tidal cycle and not necessarily extreme.

King Tide:

  • Definition: A king tide is an informal term describing the highest of the high tides that occur during the year. King tides are extreme spring tides that usually occur when a spring tide coincides with the moon being at its closest point to Earth (lunar perigee) and/or when the Earth is closest to the sun (perihelion).
  • Frequency: King tides typically occur twice a year, during specific times when the gravitational forces of the moon and sun are particularly strong.
  • Magnitude: King tides are the most extreme high tides, much higher than regular spring tides.

Duration of a King Tide

King tides are typically short-lived, lasting for a few hours at a time. However, the period of high tides associated with king tides often extends over several days. The peak of a king tide may occur twice a day, following the natural pattern of high tides, but the exact duration depends on local conditions and the timing of the moon’s orbit.

How Often Do King Tides Occur?

King tides typically occur twice a year, although they are more common in some years. These events are tied to the Earth’s position relative to the sun and moon, particularly when the Earth is closest to the sun (perihelion) and when the moon is closest to the Earth (perigee). The exact timing varies depending on the specific geography of a region, but in general, the two occurrences are:

  1. Winter (Northern Hemisphere): Around January, when the Earth is at perihelion.
  2. Summer (Northern Hemisphere): Around July, when the moon’s influence is strongest during its perigee.

These high tides are part of the natural tidal cycle, so while king tides occur predictably, the exact dates and intensity vary slightly each year based on the specific alignment of the sun, moon, and Earth.

King tides in summer and winter are not always the same in magnitude. Several factors influence the height and intensity of these tides:

  1. Lunar Perigee and Apogee: The timing of the lunar perigee (when the moon is closest to Earth) varies each year. If a lunar perigee coincides with a new or full moon during the summer or winter, the resulting king tide is more intense. For example, the August 2024 king tide was associated with the Super Moon, even though the Earth was closer to aphelion than perihelion.
  2. Solar Perigee (Perihelion): The Earth is closest to the sun in early January (perihelion), which generally contributes to stronger tides during winter in the Northern Hemisphere. However, if a Super Moon occurs during another part of the year, such as in August, it can result in a particularly high summer king tide.
  3. Local Topography and Weather Conditions: Local conditions, such as atmospheric pressure, wind, and regional geography, can affect the intensity of king tides differently in summer and winter.

Common Effects of King Tides

The impact of king tides can be significant, especially in low-lying coastal areas. Common effects include:

  • Coastal Flooding: King tides raise water levels above normal high tide levels, leading to flooding in coastal communities. This affects homes, roads, and infrastructure.
  • Erosion: The force of king tides accelerates coastal erosion, especially in areas with fragile shorelines.
  • Saltwater Intrusion: King tides push saltwater into freshwater systems, contaminating drinking water supplies and affecting agricultural land.
  • Infrastructure Damage: Roads, bridges, and other infrastructure near the coast can be damaged by the force of king tides, especially when combined with storm surges or strong winds.
  • Increased Debris: The high water levels and strong currents associated with king tides increase the debris being washed ashore, including logs, seaweed, and man-made materials.

Locations and Occurrence of King Tides

King tides occur along coastlines around the world. However, certain locations are more prone to experiencing significant impacts from king tides due to their geographical features, population density, and coastal development.

Common Locations and Impacts:

  1. United States (West Coast and East Coast):
    • California: Coastal cities like San Francisco and Los Angeles often experience king tides that produce localized flooding, particularly in areas with low-lying infrastructure and beaches.
    • Florida: Miami and other cities in Florida are prone to king tides. The tides exacerbate flooding issues, especially in conjunction with rising sea levels.
  2. Australia:
    • Queensland and New South Wales: Coastal cities like Brisbane and Sydney see king tides that cause flooding in rivers, estuaries, and coastal roads.
  3. United Kingdom:
    • South Coast: The south coast of England experiences significant king tides, leading to coastal flooding and erosion.
  4. New Zealand:
    • Auckland and Wellington: Coastal regions of New Zealand are affected by king tides. Water levels rise dramatically in harbors and estuaries.
  5. Pacific Islands:
    • Fiji and the Marshall Islands: Low-lying Pacific islands are particularly vulnerable to king tides.

Additional Facts About King Tides

  • Climate Change Connection: While king tides are natural occurrences, they are a proxy for understanding and visualizing the future impacts of rising sea levels due to climate change. As sea levels rise, the effects of king tides become more pronounced and frequent.
  • Public Awareness: Many regions affected by king tides have public awareness campaigns to educate communities about the risks and to encourage preparedness for coastal flooding.
  • Citizen Science: Some coastal communities engage in “king tide projects,” where citizens document king tides by taking photographs and recording data. This information helps scientists and policymakers understand and plan for the impacts of sea level rise.

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