Tag Archives: weather

Below Sea Level does not mean Below the Sea.

This post represents my own views and is not intended to represent the views of my employer, present or past.

I’ve been umm-ing and ah-ing for a couple of months now about whether to write this blog, but I think I have finally had enough. You see, in Hull, we are at risk of flooding from the sea, or more specifically, the Humber Estuary. This risk emerges when low pressure out in the North Sea, caused by the storms, which can be common in the winter, effectively suck up the sea causing it to raise a little. High winds whip up waves, and these add a little more height to the water. All of this has the potential to raise the level of the sea, for a few hours, by up to a couple of metres. On December 5th 2013, a storm surge (as these events are called) raised the water level in the Humber by 1.7 metres.

The added complexity to this are the tides. The difference in the water level between low and high tide at Hull, according to the Associated British Ports (ABP) is between 3.5 m for a neap tide, and 6.9 m for a spring tide – this staggers the level we have determined to be 0 m, or sea level. This means the risk of flooding is all a matter of timing. If, on December 5th 2013, the storm passed by a few hours earlier or later the surge would have aligned with the low tide, and the additional 1.7 m would have barely been noticed by anyone. However, it was timed with a high spring tide, resulting in record water levels in the Humber and caused flooding in Hull and around the Estuary.

Coastal flooding

Graphic showing how coastal, or tidal, flooding forms. This was the type of flooding which occurred around the Humber in 2013. Thanks to NERC for producing these great resources. 

When we design and build flood defences on the coast we don’t build them to just hold back tidal levels of the water, but also to defend against enhanced water levels produced by storm surges. Since 2013, the defences around Hull have been updated and a repeat of the event would result in little or no flooding in the city – I don’t know the exact level of the defence, but we can say that it is able to contain sea levels of at least 1.7 m higher than the highest natural tidal level.

A big issue facing Hull is sea level rise. Sea level has been rising since the end of last ice age, and is set to continue in the future. On top of this, the climate change caused by our industry is accelerating this. Our best estimates for the Humber area, assuming that as a species we continue increasing our influence on the climate, suggest the sea level will be around 1 m higher in 100 years than they are today – this will increase the risk of flooding and we need to ensure that the public understand this and that we continue to invest in improving the standards of our defences to keep pace.

On the first point, talking to residents of Hull about the risk of flooding from the Estuary provokes two responses. (1) There is a lack of appreciation of the risk from the Estuary, and when I start to talk about the 2013 flooding, people tend to share with me their experiences of the 2007 flooding (a surface flooding event). (2) People tend to feel that there is no point in doing anything as “Hull will be underwater in 100 years”. This latter point is what I want to discuss here, it’s a common perception and leads to a kind of apathy where people become disengaged with flood risk and actions to mitigate for it, but it is wrong.

It is a deeply held belief that goes beyond even the city – in 2015, Dr Hugh Ellis, the now Head of the Town and Country Planning Association (TCPA), made the claim that the city would be underwater in 100 years –

“We need to think about moving populations and we need to make new communities. We need to be thinking, does Hull have a future?” (Source – Daily Telegraph)

Ok, he was trying to make a valid point, one that sea level rise is going to increase the risk of flooding for coastal cities, but I don’t think bold, and inaccurate statements, like this are helpful, and they only result in residents of the areas becoming disengaged – why do anything about the problem if it is futile?

But where does this idea come from? Why are people convinced Hull will be underwater in 100 years? Why do people think it will become the “Venice of the North”? Well, look at the map below –

surging seas

Screenshot from Climate Central’s Surging Seas Risk Zone Map – this shows the Humber Region, UK, with a 1 m sea level applied.

This is map of ‘risk’ taken for the Humber area. For areas outside of the US, the Risk Map has been produced using a map of land heights obtained from space by the Shuttle Radar Topography Mission, which mapped the entire globe at resolutions between 30 m and 90 m. The areas shaded in blue are all those ‘below sea level’ – normally 0 m, but in the map above I’ve set it at 1 m to represent the predicted sea level in 100 years time. Hull isn’t labelled on that map, but it basically the large blue area between North Ferriby and Hedon – very clearly ‘under water’.

But the method is problematic, it’s too simple. An average measurement of land heights over a 30 m area is fantastic when considering it is for the whole planet, however for determining flood risk it’s a bit rubbish. It smooths the land surface, removing obstacles, like wall, roads and buildings, and crucially, flood defences. The method also ignores ‘hydraulic connectivity’*, basically meaning that for water to flood an area it has to have a source of water and a route for it to get there – flood defences work by removing this hydraulic connectivity and this is why today the Humber region, and much of Holland, is close to or below sea level, but not under the sea.

To understand the actually risk posed by sea level rise requires a more complex model, one which accounts for tides, contains more detailed data, and more importantly includes flood defences. Our model (paper here behind paywall) does this, and a version of it is incorporated into Humber in a Box – with both of these we observe no flooding around the Estuary for natural tides with a 1 m sea level rise. This is because the defences are built to hold back the much higher water levels caused by storm surges.

Climate Central have been careful to refer to this shading as ‘risk’, and not direct inundation by the sea, but the use of blue and not making this explicit anywhere opens this up to mis-interpretation where ‘below sea level’ means ‘below the sea’. This is clearly happening – see this article in the Conversation, which made the BBC Sports pages, which used the app to suggest Everton’s new stadium “could end up underwater” in the future, or this article shared by the awesome Geomorphology Rules  Facebook page, suggesting that coastal cities in the US will be “drowning in water”.

Sea level rise is going to increase the risk of flooding in coastal cities but they are not going to be under water. The risk does not emerge from the tidal water levels, which will most likely be contained by present defences, or those to be built in the future. However, the risk from storm surges will increase – the likelihood of events like December 5th 2013 is set it increase, both in strength and frequency, and with 1 m extra sea level in 100 years our defences will need to be updated to cope with the enhanced levels. This will take a lot of money, a lot of effort, a lot of political will, and this requires the buy in and support of the residents of these areas. Telling them, or suggesting, that they will be required to relocate will only achieve the opposite.

Sea level rise and the related flood risk is a complex issue and we can’t keep trying to find simple answers.

*For areas within the US, the method uses much higher resolution height data, and accounts for hydraulic connectivity by shading areas differently.

Another Storm Surge? Keep your eye on the forecasts!

There are warnings emerging of a storm surge along the East Coast of England for this Friday (13th January 2017). At the time of writing these are a low risk warning, but the situation can change so keep your eyes open for updated warnings from the MetOffice and Environment Agency, such as the Flood Information Service.

If you’ve read this blog before you will know that I have performed plenty of computer model simulations of the 2013 storm surge in the Humber Estuary. Thankfully, it does not look like this Friday’s surge will result in flooding, and not on the scale of 2013, but I thought I’d share a simulation of the latest model anyway. This is a simulation of the 2013 storm surge –

There still, as ever, more work to do but it’s getting there.

OTD Humber Storm Surge – 05/12/2013

No score and three years ago the storm surge of December 5th 2013 swept along the East Coast of England, and the Humber Estuary. There was flooding in Grimsby and Hull, and the port at Immingham was also badly flooded. One of the worst affected areas of the village of South Ferriby on the South Bank of the Humber, a few miles away from my home town of Barton-upon-Humber.

Since the event, my colleagues and I have done a lot of research and work based on this event. This post will briefly highlight some of this, how you can find out out more, and what we have planned for the future.

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At the time I was working on a project called Dynamic Humber helping to develop the CAESAR-Lisflood model. Although the original intention was to use the model to predict long-term geomorphic trends in the Estuary, basically how we can expect the mud and sediments to move and change over time, the storm surge changed the focus to flood risk.

We published our work on this in early 2015 – see the academic paper here.

The modelling technique was developed for other areas by my colleague Jorge Ramirez, and this research can be seen here.

This research led to us using our modelling to help the Environment Agency, and this work is ongoing still. We are also seeking to further the work of simulating the sediment processes within the Estuary,and understanding how this might influence future flood risk.

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One of the enduring images of the event was the breach it punched in the spit-like feature at mouth, Spurn Point. For nearly two centuries Spurn has essentially been a man-made structure, and its origins, true nature, and hence its future, are largely a mystery. Read more on this here.

In Easter 2015, a PhD project was begun to try and model the future of Spurn Point, merging a model of the North Sea with our model of Humber.

Finally, SeriousGeoGames emerged as a direct consequence of this event and our modelling of it. The first application, Humber in a Box, shows a simplified version of our Humber model in an attractive, immersive, virtual reality environment. By raising the sea level we can see how flood risk in the Estuary is likely to change over time.

Humber in a Box

If you have a Cardboard-style headset, try the YouTube demo here.

I’m currently working with some talented students from SEED Software on the second iteration of Humber in a Box, called TideBox. We hope to make the application more ‘self-led’ and more generic about estuaries and tide, making more accessible.

There are likely to be lots of exciting developments in 2017 and I will bring you them as soon as I can.

 

 

Hurricane in the Humber : Modelling the Unthinkable

We’ve all been stunned by the images of Hurricane Matthew tearing through the southern States of the east coast of the USA, and the footage of the resulting storm surge sweeping into these coastal areas. We should not forget Haiti and the carnage once again unleashed on this nation, and the ongoing struggles the people will have there for years to come. The power of nature can simultaneously be awe inspiring and horrendously destructive.

In the UK we are relatively blessed in our sheltered position from natural disasters – it is difficult to imagine just what it is like as a nation to suffer an event on this magnitude, just as we could scarcely imagine what the impact of an earthquake or a volcano might be. But what if the unthinkable did happen? What if Hurricane Matthew did hit the UK with the full force of a Category 4 or 5 storm? How would the storm surge look like?

My research involves using numerical (computer) models to understand how nature works, in particular the movements of water. In the past I have used these models to simulate the workings of the Humber Estuary, UK, and some of that work includes simulating “worst case scenarios”. Before the 2013 storm surge this was often thought to be equivalent of the 1953 event, but now the baseline is 2013. On December 5th 2013, a storm in the North Sea caused a storm surge of around 1.8 m to form, coinciding with a high-tide resulting in the storm tide1.

1To pose a threat a storm surge needs to coincide with a high-tide. This combination is called a storm tide. A surge which coincides with a low-tide probably will not pose a risk, and the peak water levels will usually be lower than that of a normal high-tide. This obviously depends on the size of the surge and local difference between low- and high-tides.

A category 4 or 5 hurricane hitting the Humber and the UK at that strength is way beyond our “worst case scenario”, and reveals little to us about the nature of the Humber and the state of our defences. However, simulating it does provide prospective of the scale of the event and helps us understand just how powerful and destructive they are. At St Augustine, Florida, the surge was estimated to be 2.75 m, adding this swell to the tidal sea level – looking at the surge from 2013 this is nearly 1 m greater.

The represent this in our Humber model I have done nothing more sophisticated than simply adding 1 m height to all the water level data we use to simulate the 2013 flooding. The video below shows the results – it looks pretty bad and it would be, but we need to consider some aspects of the model to fully understand what we are seeing. The model uses a smooth representation of the land surface, as in it has no buildings, walls, roads, hedges, tree etc which would stop or slow the flow of water, although it does have a representation of flood defences. This means once the water levels exceed the defences and spill over on to the land the water can just keep flowing, when in reality it would be stopped by obstacles – so the area flooded in the model is larger, yet probably shallower, than we would expect.

This is truly an unthinkable event and we would not expect a surge of 2.75 m to be seen in the Humber. However, global sea levels are rising and our best predictions suggest that the base sea level in the Humber will be around 1 m higher in 100 years time – from this point, the 1.8 m surge from the 2013 event would cause water levels of the same height as a 2.75 m surge in the present day. As our climate warms, providing more energy to the atmosphere, we can also expect our weather to become more stormy and events like 2013 will become more common. This paints a bleak picture and presents coastal areas like the Humber a major challenge for the rest of this century.

The good news is that those responsible for our flood defences are aware of this challenge and are developing their plans to help us face it. Our model is already out of date as several areas around the Humber have had their flood defences improved since 2013, and there are plans for more – this process will be continuously assessed and developed in the future to keep people and property safe. Models such as our will be used to test those plans and the contribute to designing new schemes. The challenge is great but we can meet it.

Musical Rain-gauges at the Prague Quadrennial 2015 @PQ2015 #PQ2015

A couple of weeks ago I used some of my annual leave to accompany my wife, Amy, to the Prague Quadrennial of Performance Design and Space, or PQ, where she was giving a paper. Amy had tried to explain this to me as like an “Olympics of Scenography” – where nations exhibited examples of performance design and space to the 180,000 people who are estimated to have attended the event. She was, of course, summarising it as basically as she could for me, as the event was a whole lot more than that description.

If, like me, you are unfamiliar with Scenography, Wikipedia describes it as “the study and practice of performance design”. For me the most interesting aspects were the studies of space, and how people related to spaces on stage and around them. From the talks, exhibits and the materials in the book shop, it was clear that there is a very strong cross over with disciplines like architecture – this appealed to the former Planner in me.

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It was very nice to see Amy (middle in the picture above) present her paper – it was the first time I’ve had the chance to do so. The room she presented in was very impressive and grand, although the geology on the walls was painted on (in fact, even one of the balconies was painted). My appalling photography skills doesn’t really do it justice.

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As I had a three-day pass, it gave me an opportunity to explore the exhibits spread across the Old Town of Prague. One of the themes was ‘weather’ and as a hydrometeorologist I was keen to see what had been created.

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Above is Sound of Music (in a Box). After spending so much time working with River in a Box and Humber in a Box, anything called ‘in a Box’ is going to grab my attention. This was part of Finland’s exhibit, where this piano had been left on a beach for a full year, experiencing the four seasons and then played. A recording of this could be heard via the headphones.

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‘Melting Point’ was another exhibit by Finland and this grabbed my attention. You can see a video of this below. Here microphones were used to record the sounds of blocks of ice melting, and the drops falling into a pool underneath. This reminded me so much of Rolf Hut’s TED talk about the acoustic disdrometer – I wonder if music could be made by recording the passage of storms over a network of rain-gauges?

Although I was a long way out of my expertise looking around the exhibits, I really enjoyed viewing, experiencing and engaging with them, and discussing them with Amy. At the same time, in the same city, was the conference of the International Union of Geophysics and Geodesy – I really think that many of the delegates there would have enjoyed and been inspired by many of the exhibits at PQ, and vice versa. It’s a shame that we rarely get to experience things outside of our immediate disciplines even when two large, influential meeting coincide in the same city.