So what are super tides?
Tides are governed by the gravitational pull of the moon and, to a lesser extent, the sun. Because the sun and moon go through different alignment, this affects the size of the tides.
When the gravitational pull of the sun and moon combine, we see larger than average tides – known as spring tides. When the gravitational pulls offset each other, we get smaller tides known as neap tides. We see two periods of spring and neap tides roughly every month.
However there is a longer cycle at work too, associated with the gravitational pull of the planets in the solar system. This means we can see additional, albeit relatively small, increases and decreases in the size of spring and neap tides over long periods of time.
We are currently at the height of those increases, so the astronomical tide is at an 18-year peak – although this is only a few centimetres bigger than a more average spring tide.
What is the role of the weather in sea levels?
Large astronomical tides don’t necessarily cause the highest sea levels we’ve seen – even in the last few years. That’s because the weather can have a much bigger impact on sea level than the 18-year tidal cycle.
Strong winds can pile up water on coastlines, and low-pressure systems can also cause a localised rise in sea level. Typically, the difference in water level caused by the weather can be between 20 and 30cm, but it can be much bigger.
On the 5th December 2013, for example, the weather created a storm surge that increased the water level by up to 2 metres. Although an estimated 2,800 properties flooded, more than 800,000 properties were protected from flooding thanks to more than 2,800 kilometres of flood schemes. The Environment Agency also provided 160,000 warnings to homes and businesses to give people vital time to prepare.
This highlights the importance of the Met Office and the Environment Agency working together to look at the combined impact of astronomical tides, wind, low pressure and waves on flood schemes to assess the potential impacts for communities around our coast.
© Met Office / Environment Agency
