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The path of future rainfall will not be smooth

person walking on street and holding umbrella while raining with vehicle nearby
Written by Catherine McBride

UK rainfall is volatile and long-term water shortages are rare. But UK water companies and farmers dependent on water should be collecting the extra rainfall when it comes. Deeper reservoirs could help while a guaranteed minimum provision for their customers would force water companies to think about how much water they store.

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We are having a long hot summer in the UK, an unusual event. We know this because we have lots of data: the UK Met Office has historical data from all of its stations on its website: mean daily maximum and minimum temperatures, days of air frost, total rainfall and total hours of sunshine.

For the Heathrow Met Office station this data starts in 1948. For Oxford it starts in 1853. It is fascinating – if you like pages of numbers (I do). I even downloaded the monthly rainfall data and calculated the mean and standard deviation. (50.5mm and 29.7mm, if you are interested) that means that 68.27% of the monthly rainfall in Heathrow was between 20.8mm and 80.2mm – if rainfall were normally distributed. It isn’t, as rainfall can’t go below zero while the upside is technically unlimited, although since 1948 there has never been zero rainfall recorded by the Heathrow Met Office and the highest rainfall recorded was 174.8mm in Oct 1987 when a hurricane hit the UK – so not actually unlimited either. However, the UK commonly has monthly rainfall spikes above two standard deviations from the mean. There have been spikes in rainfall of between 110 – 160mm in: 1949, 1951, 1956, 1960, 1970, 1974, 1977, 1987, 2000, 2002, 2009, 2013, 2020. So rather than worry about the occasional drought – maybe we should be thinking about catching these rainfall spikes when they occur. Unfortunately, the UK press is uninterested in above average rainfall. You are more likely to hear weather reports about hot weather next week or next month than to hear that this week will have rain, again. The British just take rain in their stride but are shocked by a brief drought.

Although, the media like to compare this year’s low rainfall with 1976: in the first seven months of 1976 the Heathrow Met Office had recorded about half of the precipitation we have had in the first seven months of this year. In seven of the first eight months of 1976, the Heathrow met office recorded less than 20.8mm of rain, only totalling 97.2mm, but then in each of September, October and November they recorded over 80.2 mm. So, by January 1977, the 12-month average rainfall was back into the normal range. In contrast, this year we have had 182.2mm of rain from Jan to July – at least at the Heathrow station.

However, despite the media attention given to 1976, this wasn’t the UK’s only dry year. May 1972 until March 1973; March to July 1990, and more surprisingly, (because it is rarely mentioned by the press) from January 1996 to April 1998 – for two and a quarter years, the UK survived with rolling 12 month average rainfall below the normal range. I like to look at rolling 12-month averages as it evens out the variation in the number of days in a month. Getting less rain in February with only 28 days, than in January or March both with 31, may have nothing to do with the weather. The mean of the rolling data is almost the same as the monthly data, 50.6mm, but the standard deviation is much tighter at only 8.9.

However, if we are worried about droughts – July 2022 isn’t that bad. In August 1995 the Heathrow Met Office recorded a mere 0.3mm of rain. That is 4% of the amount recorded in July of this year (7.6mm). As I mentioned before, there is no month with zero rainfall recorded at the Heathrow Met Office Station. The Oxford data runs from 1853 and similarly has no month with zero rainfall, although April 2011 had only 0.5mm and April 1893 had only 1.5mm and April 1984 had only 1.6mm. Cambridge Met Office rainfall data starts in 1961 but also has no months with zero rainfall. The lowest is 0.5mm in Jun 1962, them 0.8mm in Jun 2018 and 1.0mm in April 2007. Although, the Eastbourne Met Office has recorded 0.0mm of rain twice – once in Feb1959 and 63 years later in July 2022.  By the way, if you still believe in ‘March winds and April showers’ – the data doesn’t back that up. April is the month most likely to have under 10 mm of rain in the London, Oxford, Cambridge triangle.

However, my point is not to critique nursery rhymes, but to talk about whether the UK needs to build more reservoirs. And water storage is not the only British infrastructure stretched to its limits. This summer we have discovered that UK roads melt at 40 degrees Celsius, that our train tracks don’t have expansion gaps to stop them buckling, that many UK farmers don’t have any water reserves, irrigation equipment or boreholes and that the grass in London’s parks turns brown after a few days of heat. All of these things can be fixed. However, the reason the UK doesn’t employ engineering methods or grass varieties used in hotter countries is economic rather than a lack of engineering skills or resilience in public infrastructure. There is on average no need to spend the additional money on road surfaces and train tracks so that they can survive 40˚C in the Summer, (or -30˚C in the Winter) if our weather reverts to type after a few months. And we have lots of Met Office records to prove that it does. In short, you get the infrastructure you are prepared to pay for.

However, as the 12-month average rainfall rarely stays outside its normal range for more than a few months, UK farmers have never learnt to cope without water. Certainly, if this hot/dryish weather persisted they would soon adopt the irrigation techniques used by countries not blessed with such water resources (most of the rest of the world) but they would also need boreholes or irrigation channels or their own reservoirs.

When considering irrigation channels, it is worth looking at UK rainfall rather than just English rainfall. Because while the Southeast has been parched this July, the Northwest has had normal rainfall, but the west coast of Scotland has been deluged. It would make a lot of sense to catch this water to sell to farmers or water companies in the southeast when required.  George Eustice, the Defra minister, has recently proposed a west east water channel, to move winter flood water from Shropshire to reservoirs in Norfolk for use in the summer. Either proposal would necessitate building a pipeline, a system of irrigation canals or even repurposing some disused transport canals. This isn’t impossible. In the 1700s British engineers were building canals for coal transport all over England. The irrigation canals of Australia’s Murrumbidgee Irrigation Area were started in 1903 and now irrigate 1,600,000 acres of cropland in Southwestern NSW with water from the Burrinjuck Dam over 600km away. If Australia can do this, the UK can. Although the difference is that Australian farmers need the water (almost) every year. Whereas in the UK it would only be needed in extremis. So would the investment be worth it?

I know a bit about overcapitalising your infrastructure. I refurbished a house in 2006 – taking it back to bare bones and rebuilding most of it. Being an eco-warrior at the time (yes, me) and listening to the BBC tell me that the hot dry weather was here to stay – besides insulating the walls and floors, I installed solar hot water panels as well as a large rainwater collection tank and a drip irrigation system. Sixteen years later, while looking at the Heathrow Met Office data, I noticed that 2006 was a particularly hot dry summer, with a mean daily maximum temperature of 28.2˚C. I had to wait until July 2018 to get a hotter month – 28.3˚C. Even this July, irrespective of the media hullabaloo, the mean daily maximum temperature was only 27.2˚C. I will admit that both the heating engineer and the plumbing company advised me that I would never get my money back on the solar panels. But this year, my overinvestment is giving me a return. As it did in 2010, 2013 and 2018.

So, should the government be responsible for upgrading the UK’s infrastructure? Probably not.

If you are running a business that depends on water – like farming – then having your own water supply in a reservoir, drilling a borehole or even collecting the water from the barn roof in a tank should be part of your business plan. (A water tank connected to the roof downpipe was part of every farmhouse in Australia – even if the water was only used to stop a bushfire burning down the house.) Under the Farming Transformation Fund, Defra will give farmers a grant of 40% of the total cost to build a reservoir, paid in arears, provided it is for an arable or horticultural business growing irrigated food crops, ornamentals, or forestry nurseries and the farmer owns the land or has a tenancy for at least 5 years after construction is completed. The list of things that Defra will not pay for is long and includes both boreholes and water storage that will be used to feed livestock. This seems unfair but Defra regulations are more concerned with flooding and farm runoff getting into rivers than with water provision during a drought. No doubt they have also looked at the Met Office data.

However, if Defra is prepared to build a dam and pipeline to redistribute water from Scotland or Shropshire to other parts of the country – then this could be a viable business and they should be able to charge for the water, as the people who buy it will be charging for their produce. However, if they have prevented their potential customers from building a reservoir/borehole/rainwater tank then this may be viewed as opportunistic rent seeking.

Similarly, if you are running a water company then reservoirs, extra reservoirs, and reserve reservoirs must surely be part of your business model. Especially if you are providing water to a region with an expanding population such as Southeast England. A privatised water company should be responsible for having adequate provision for their customers – who after all have nowhere else to take their business. Maybe a water contract should not just charge people for the water they use but also guarantee them a certain amount of water each year. Such a requirement would force companies to think about how they store and preserve water. It might also make their customers think about how much they are using. Although this could also limit new house building to the increase in water storage.

But when we talk of building new reservoirs to supply an increasing population, we run into a different type of eco-warrior: they are not worried about CO2 emissions or apocalyptic future droughts but about the habitat loss caused by new reservoirs – allegedly. For example, the proposed Abingdon reservoir near Oxford is being opposed by activists who claim it would ‘have a “catastrophic” effect on wildlife and cause significant disruption to residents.’ I suspect that they are more concerned about the later than the former – as wildlife is exceptionally good at getting out of the way of rising water, provided they are not fenced in. But would the residents still feel disrupted by the reservoir when they have water during the next drought?

However, increasing a reservoir’s capacity may not require a new structure – we could simply make existing ones deeper. Deeper reservoirs have the advantage of having a smaller surface area compared to the volume of water, so there would be less evaporation as well as fewer protesters. While water levels are low, it could be a good time to pump out the remaining water and start digging, especially as the drought in London was well and truly broken this week. (I know this because after 3 days and nights of heavy rain my almost empty rainwater tank is full again.) Alternatively adding a few metres to an existing dam wall could vastly increase its capacity although most probably also increase the surface area and subsequent evaporation.

Some climate scientists believe that the UK will become hotter or drier in the future, I don’t have enough data to comment on this, but looking at the past 70 years I can predict that any change is unlikely to be smooth. Perhaps we are concentrating too much on the long-term averages and overlooking the volatility. The UK is most likely to see above average rainfall as well as below average rainfall for many years before any apocalypse – so why not start catching the water.

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About the author

Catherine McBride