Sea Change for Hull

“I’ve been working in flood risk management for over 20 years trying to help make good decisions,” says Dobson. “It’s often pretty static – lots of modelling, lots of economics presented in a static report with conclusions at the end. We wanted to see what else was possible and bring it to life. Cambridge University managed to unblock the complex modelling which allowed us to do that.”

Rising Sea Levels
“Hull is low lying – it’s similar to New Orleans in many ways due to its low lying nature on the coast – and there are 100,000 properties potentially at risk from the most extreme weather events,” says Dobson.

As much as 90% of the city is below the high-tide line. The Environment Agency has warned that, with the changing climate, water levels in the Humber Estuary could rise by over 1m in the next century.

In March 2022, a scheme of new flood defenses was opened in Hull funded by £42 million from the government. Then in May 2022, an Environment Agency project to create a large ‘aquagreen’ that will reduce flood risk to over 870 properties and key infrastructure in east Hull began.

“These measures are key elements that reduce the likelihood of flooding to homes, schools and businesses throughout Hull,” explains Dr Susan Manson, Humber Technical Manager at the Environment Agency. “The size and scale of investment in the tidal defenses has been an important driver for investor confidence such as the Freeport bid.” (Freeports are a government program that aim to create economic activity near shipping ports or airports.)

But we’re facing “a losing battle” against sea-level rise says Spencer: “We’re going to see more extremes and those extremes from a coastal point of view are going to be sitting on top of a rising baseline which is going to increase as we move towards the end of the century – not just in Hull but everywhere.”

Spencer’s team at the Cambridge Coastal Research Unit are experts on coastal environments and the dynamics of sea-level rise. Their work has taken them all over the UK, from the salt marshes of Norfolk and Essex, to the estuaries of Suffolk and Lancashire, and the embayments of The Wash and Morecambe Bay, working with communities and organizations to manage the coast for the future.

And so Spencer, Dobson, Downie and their partner organizations were tasked with finding a better way to understand and communicate the impact of rising sea levels as part of the EuroSea program. EuroSea is a large-scale project to improve the European ocean observing and forecasting system, involving 55 partners from 16 countries and funded with Euro 12.3m from the European Union’s Horizon research and innovation program.

New Digital Tool
Typically, flood risk assessments only consider a limited band of uncertainties around sea-level rise. The challenge with managing this risk is that as projections get further from the present day, the uncertainty of the prediction increases.

There’s an added problem that discount rates applied in economic Net Present Value financial calculations also mean that the impacts of worst-case scenarios later in the century have limited impact on decisions we are taking now.

Spencer and his colleague Dr Elizabeth Christie started with detailed sea-level rise prediction information from the UK Climate Projections data in 2018 (UKCP18) to model the impact of climate change.

Then they developed a framework that incorporates sea-level rise uncertainty into coastal flood risk assessment by streamlining the process of modelling sea levels, wave overtopping and flood spreading on land. This allows all the uncertainty to be propagated through to the calculation of risk, driven by economic damages.

The outputs were in a coarse gridded format initially, but Spencer and Christie worked with CADA Consulting, the Data Scientists supporting Arup, to reduce the resolution to a level that would allow the speed of processing required for live user interaction.

The conclusion was to divide Hull into 1,000 virtual hexagons 400m wide from corner to corner. This lower resolution at ground level meant they could speed up the processing of a huge number of results from different sea-level scenarios and their economic impacts in real-time using a web-based tool.

“It was the first time we’d ever done anything that has actually captured the uncertainties in a way that allows you to talk to policymakers,” says Spencer.

By the end of their research, the Cambridge team was running in the order of 10 million data points relating to 21,300 scenarios with 122 increments of sea-level rise and seven extreme water levels in just a few hours.

Throughout the project, the team valued the input of the Environment Agency: “they were an incredibly important part of this project to make sure what we were doing was sense checked and was potentially useful for users at the end,” says Dobson.

“Cambridge University did the analytical heavy lifting,” adds Downie. “As a result, they could statistically describe a really broad spectrum of scenarios we were able turn into a prototype tool that allows users to delve into the data by toggling variables like time, storms and tides, defenses and so on – and then compare outcomes in terms of scale of flooding across a geographical area.”

Beyond Hull
The Cambridge modelling and the sea-level rise insights tool has given the Arup team new levels of data and new opportunities to improve insight for decision makers.

Can it be applied in places beyond Hull? ‘Yes’ says Dobson – wherever local levels of sea and land are known. “We’ve worked with Cambridge to design the whole process to be replicable. We want it to be globally applicable.”

The team don’t see the tool as a replacement for detailed modelling to design defense levels, but they see real potential for it to be used as a scoping tool to set the boundaries of detailed modelling. In other words, using the tool to understand which scenarios identified by the IPCC are most important for a location and then spending often limited resources to understand the detail where it is needed.

Dobson sees the tool being applied to towns, cities, regions and even small countries around the world so that they can make better early-stage decisions to prepare for climate change and, just as important, help explain these decisions to the public. Manson also sees its potential in facilitating conversations about resilience and adaptation in line with the National Flood and Coastal Erosion Risk Management Strategy.

They acknowledge that there will be a play off between the needs of coastal decision makers, who may want more detail, and those seeking to communicate to the public, which warrants more visualization. But both of these requirements add processing time, slow the calculations, making interaction less dynamic. “So where is the balance of speed vs need?” poses Dobson. “This is something to be explored in future.”

Meanwhile, the team has been spreading the word to UK policymakers through a Parliamentary and Scientific Committee and, with Spencer and Downie, at a United Nations interactive workshop as part of The Ocean Decade - The Science we need for the Ocean we want.

“The power in what we’ve done is that we’ve brought all of the science through from the front end through to decision makers with the visualization prototype,” says Dobson.

“This work is about the huge decisions that society has to make about adapting for climate change,” adds Downie. “We just don’t know how things are going to play out and we’re only going to get a few chances to get these things right. It’s simply better to make good decisions and this tool will help this by capturing future sea rises in the economic decision process.”

Louise Walsh is Editor, Research Horizons, University of Cambridge. The article, originally posted to the website of the University of Cambridge, is published courtesy of the University of Cambridge.