Spring Tides
The Earth, moon, and sun are in near-alignment approximately every 29.5 days. When this happens, the moon is in a Full or New phase and the gravitational pull of the sun is ‘added’ to the pull of the moon, exerting a force on the oceans that causes high tides to be higher and low tides to be lower.
Perigean Spring Tides
Sometimes, the moon is in its New or Full phase at the same time as its orbit is closest to Earth. This causes the highest predicted tides of the year because the moon is exerting its greatest gravitational pull. Some people will refer to these tides as King Tides.
Sea Level Rise
The average height of the world’s oceans is increasing. The major driver of sea level rise is global warming, which is causing warm ocean water to expand and polar ice to melt. Locally, we have observed over a foot of sea level rise in the past 100 years and the rate of increase is accelerating. Our daily tides are getting higher, with or without the presence of spring tides or storm effects.
Coastal Storms
Onshore winds and changes in barometric pressure from coastal storms often lead to coastal flooding and erosion. Storm surge results from an abnormal rise in sea level above the predicted astronomical tide. This results in a Storm Tide, which is a combination of storm surge and the astronomical tide.
Did You Know?
Delaware has the lowest average land elevation in the entire United States! High tides can cause beach erosion and flood low-lying roads and properties, even in the absence of storms.
Danielle Swallow is a certified climate change professional with Delaware Sea Grant (www.deseagrant.org). Delaware Sea Grant utilizes research, education, and extension work in support of resilient communities, economies, and coastal resources. Danielle provides technical assistance and outreach to communities on emergency preparedness and building resilience to weather and climate hazards. She is co-founder of the Resilient and Sustainable Communities League (RASCL – www.derascl.org) and loves hiking the Gordons Pond Trail in Cape Henlopen State Park.
