When, where and for how long will it rain?

06 Sep When, where and for how long will it rain?

There are two things we know for certain in Britain. Either it’s raining, or it is going to rain. What we are less sure about is how soon, how much and how often, and how that translates into flood protection.

As I hope to show, a mix of software modelling, very practical site preparation, plus emergency evacuation and business continuity procedures, are our best first line of flood defence.

But why is this particularly important now?

The answer seems to be that the nature of flooding incidents is changing quickly – significantly faster in fact, than climate scientists were expecting according to the UN’s hard-hitting August 2021 report (https://www.ipcc.ch/sr15/). I would like to dig into all this further.

Rains stops play

Summer 2021 has been damper than usual, not only in far-off Asia and China but also across Europe and in southern England. Yorkshire, where I am sitting, has been spared … so far!

A key question for most of us as individuals and businesses must be whether a traditionally wet UK is now becoming even wetter … albeit at different times, in different places, and in different seasons?

We shouldn’t be surprised if the answer is yes. Warm air carries more water and is more energetic. Climate change, the UN report says, makes violent unpredictable storms more frequent. Critically, they are also slow-moving.

Ready aye ready

Unfortunately, one million UK homes have more than a 1% chance of flooding in any given year; there is also a 25% chance of severe drought before 2050 (https://nic.org.uk/themes/water-floods/).

Fortunately, we have an expanding arsenal of high-resolution fluvial modelling solutions that together with detailed site surveys allow us to assess risks accurately. We also have a range of tools and catchment scheme solutions to help us protect both single businesses and property clusters.

Theory and case study practice

I would like to show how we can use these to provide protection before, during and after extreme weather events.

The key is being able to analyse and respond to short-, medium- and long-term risks that could be changing rapidly. I’ve approached this in a number of ways.

The first is to recognise that subtle changes in the weather above us are altering probabilities down here on terra firma.

The second is to explain how Enzygo can help in managing these risks; I believe the best flooding strategy is preparation, preparation, preparation!

Thirdly, I look at the research which proves that we need to take the rising probability of intense precipitation and flooding very seriously – preparations are not an insurance policy but a survival priority.

What rising risks mean

To take the first point, slow-moving rain has several implications. Number one is a rise in destructive flash floods from water with nowhere else to go. Number two is that we cannot protect everything everywhere all the time.

These lead to number three, a swing away from building hard defences that physically hold back water in favour of learning how to live with water temporarily. In other words, ‘if you can’t beat them, join them’ – a move from resistance (mitigation) to resilience (adaptation).

The Government’s critical independent advisor, the Climate Change Committee (CCC), says the UK as a nation is doing far too little strategically to adapt to this future.

However, we can certainly help locally!

Wider still and wider …

Number four is that the Environment Agency has a preference for catchment-wide natural solutions designed to pre-empt flooding before it impacts individual properties. This is illustrated in the case study detailed below.

The strategic idea is to hold rainfall back until all, or most, of it can drain away naturally. Our tools include plants and trees, soggy moorlands, and artificially-made ‘soakaways’ to retain water.

Number five is that plans put in place today must be flexible enough to accommodate continuous future changes.

Changing odds

Seasonal patterns are changing. Randomness also means that – within broad boundaries –a month’s worth of rain could fall in days almost anywhere. Equally, many locations may be safe and unaffected for years.

Picking up my second point above, this alters the odds, which is why Enzygo uses a range of predictive tools to calculate realistic risks.

Calculating the odds

For example, if a client in a basic case is comfortable with a particular level of risk, we can identify the best response measures and their costs. This may mean paying for defences designed to hold back a likely but moderate level of flooding – and living with a low probability of higher more damaging water levels.

However, if the likelihood of higher water levels rises, our attitude to risk may change too. We might then be more willing, for example, to pay for more costly defences needed more often.

Decisions when the chips are down

This is where the mitigation v resilience balance comes in – knowing what we can change and living confidently with what we can’t … without relying on umbrellas and buckets!

Enzygo (https://enzygo.com/), as a highly-experienced independent multi-disciplinary consultancy, is able to offer a full range of integrated professional support to help pinpoint the most appropriate answers. Specifically, we provide flood defence services, emergency response and business continuity assessments (https://enzygo.com/services/hydrology/).

Advanced flood risk management

This case study puts the principles above into practice (https://enzygo.com/projects/stockport-flood-risk-and-riparian-ownership-analysis/).

The Stockport Homes Group (SHG) (https://www.stockporthomes.org/) is responsible for circa 11,750 homes in Greater Manchester.

It needs to be aware of any increasing flooding risks these properties face. However, it is also important that its staff can access, understand, and respond quickly to well-presented flooding data.

Enzygo made this possible with a GIS analysis that SHG now uses to focus quickly on specific properties where flood risk mitigation measures could be most needed.

By collated Environment Agency (EA) river and surface water flooding information across SHG’s entire portfolio area, and using freeware GIS software QGIS, we were able to compare centroid point (the middle of a triangle) data for the OS locations of all addresses against known flood zones.

This extra raw spreadsheet data is available for SHG to use whenever needed.

– Easier and faster staff data access

Using Google-powered mapping on a web-based platform (cluster map), we also made it possible for data outputs to be seen on a web browser by staff with no specific GIS software knowledge. They are now more aware of key flood risk issues affecting both SHG’s and adjacent properties.

Using a simple buffer of all known watercourse/culvert centrelines applied to Stockport Council and EA data, we also made it much easier for SHG to understand any potential riparian (river) ownership and associated responsibilities issues.

– Better risk information

SHG can now see quickly whether individual properties are near watercourse/culvert assets. Further analysis of some property title boundaries can then show if these assets are within actual ownership boundaries.

Key information on flood depth, velocity and hazards, plus a refined analysis of properties closest to, or encompassing, such assets is being added. We are also working with SHG on flood mitigation measures using our extensive knowledge of flood evacuation, training and documentation.

Not doing enough … and doing it too slowly!

I said earlier I would look in more detail at the growing evidence that we face a growing crisis.

We are not the only ones concerned about wet weather and flooding preparations. There is “alarming” new evidence of a widening gap between the climate risk and our rate of adaptation.

The Climate Change Committee’s “Independent Assessment of UK Climate Risk” as part of its advice Government for the “UK Climate Change Risk Assessment (CCRA3) Technical Report” (https://www.theccc.org.uk/publication/independent-assessment-of-uk-climate-risk/) notes more than 61 climate risks and opportunities affecting all aspects of UK life that must be tackled urgently.

The UK can meet these risks, it says, but has not done so. Acting now will be cheaper than waiting until things get worse. It puts the onus on government, but says it is in the interests of individual companies and organisations to act early … often with wider knock-on benefits.

CCC lists community benefits in eight risk areas: – diversity and habitats, soil health, carbon storage, crops, livestock and trees, food, the economy, health, wellbeing and productivity.

Why is flooding increasing now?

Climate change science is complex. Researchers think the rapid Arctic warming is slowing weather systems down by decelerating high-level winds like the jet stream, a phenomenon already linked to devastating heatwaves in Russia and floods in Pakistan. But Europe is also in the cross-hairs.

Devastating European flash floods more often

Rather than being random, flash floods across Europe may be part of a growing pattern. Researchers estimate that by 2100 Germany could face slow-moving storms 14 times more often than today (https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2020GL092361)

A Newcastle University-led study also confirms that even if global temperature rises stay below 1.5C, ‘locked in’ changes will still make flash flooding a common urban problem around the world.

The Met Office also warns that Britain could face an extra millimetre of rain on the wettest days by 2050 (https://inews.co.uk/news/record-breaking-october-rainfall-10-times-more-likely-by-2100-says-met-office-909991).

Record rainfall seen in October 2020 is now three times more likely than without climate change and could be 10 times worse by 2100. On 3 October 2020, the Met Office Hadley Centre Hadley says an average 31.7mm fell across the UK – more than enough to fill Loch Ness with 7.4 cubic kilometres.

New homes in poorer areas face increasing flood risk

Another factor is that building new homes in poorer neighbourhoods on vulnerable flood plains could lead to further problems (https://iopscience.iop.org/article/10.1088/1748-9326/abec04).

A study shows that new houses built in England and Wales from 2008 to 2018 are more likely to face higher flood risks by 2050 than affluent areas; homes near the Thames, Trent and Humber are potential hotspots.

In the last decade, more than 120,000 new homes in England and Wales were built in flood-prone areas, the researchers add.

Climate change shifting UK’s high-impact weather

The Met Office has also looked at how extremely hot UK days, or days with heavy rainfall or very cold conditions, could be affected by different levels of global warming – with significant impacts on health, transport, agricultural and energy (https://www.metoffice.gov.uk/about-us/press-office/news/weather-and-climate/2021/climate-change-shifting-uks-high-impact-weather).

Extremely hot days could increase four-fold – a 2.0°C global warming temperature rise could increase annual days above 25.0°C from some 10 to 18.

There could also be three more English days a year with high-impact rain, severe weather warnings and river flooding – up from seven (6 to 9) today. A 4.0°C increase could push this to eleven (10 to 13).

Statistics also show that the 30 years from 1991 to 2020 were 0.9°C warmer than 1961 to 1990; East Anglia and the east Midlands saw an average increase of more than 1°C.

Wetter too

The UK was also on average 6% wetter from 1991 to 2020 than 1961 and 1990; six of the ten wettest UK years recorded since 1862 have been since 1998.

2020 was the first year with annual rainfall, temperature and sunshine values all in the top ten.

It was the third warmest, fifth wettest and eighth sunniest on record (https://www.metoffice.gov.uk/about-us/press-office/news/weather-and-climate/2021/climate-change-continues-to-be-evident-across-uk).

Please feel free to contact me at any time to discuss in confidence any of the issues above.