Science: Raincoats in a drought?: Michael Price explains Britain's water shortage

IT WILL be of little comfort to those householders in the South- east who have been banned from using their garden hoses for most of the summer, but the trend is for the British climate to get wetter. The decade of the Eighties was the wettest so far recorded.

The average annual rainfall is 1,090mm; multiply that by the land area and it works out at 250 thousand billion litres a year, or 12,600 litres of water per person per day. Why, then, are we still subject to hosepipe bans?

The problems arise from the way water is distributed. Draw a line from Teesside in the North- east down to the Isle of Portland in Dorset. The majority of the population - and the major agricultural users of water - lives to the south-east of that line, where there are few suitable sites for reservoirs, land is expensive and rainfall is low. Most of the rain falls to the north-west of the line.

These factors are mainly governed by geology. Much of north- west Britain is made up of old, hard rocks that form high ground and give rise to thin, poor soils. The weather systems that sweep in from the Atlantic deposit their moisture as the air is forced up over the hills, and the deep valleys in between provide ideal reservoir sites to catch the water that runs off the impermeable rock. In the South-east, most rock is younger and softer, forming lower ground, which receives much less rainfall, and often giving rise to fertile soil. Much of this rock - notably chalk - forms porous and permeable layers called aquifers; these absorb what rainfall there is and hold it in store, releasing it slowly to rivers, wells or boreholes. Chalky ground supplies only about one-sixth of Britain's water, but some towns and cities in the South and East are dependent on this source.

The distribution of rainfall is even more significant if we look at a map that distinguishes between the winter months of October to March, and the summer period from April to September. Then we see a great swathe down eastern England, where rainfall in winter is much lower than in summer. Because plants need more water in their growing season, between April and September, they dry out the soil. Any rain that falls is greedily absorbed and does not replenish aquifers. The amount of drying out that occurs is expressed as a 'soil-moisture deficit' (SMD), which is the amount of rain needed to wet the soil to the point where it stops absorbing water.

The SMD cannot increase indefinitely. As the soil dries and it becomes harder for plants to extract water, they begin to wilt and die. Typically, SMDs in the South- east begin to increase in April, rise to a little over 100mm in July and then decline through the autumn, usually being eliminated in November. Winter rainfall then recharges aquifers or fills reservoirs.

The last few years have not been typical. The Atlantic depressions that bring rain have tended to bypass Britain. The west-east decline in rainfall has been accentuated by this, and by the scarcity of the thunderstorms that usually bring rain to the East in summer. The result has been that the SMDs have lasted in the South-east through to the early winter and, in some cases, to the following spring. Last summer's SMDs persisted in much of the South-east until this spring, and began to develop again almost immediately.

The heavy rainfall in early July has helped the situation. It will have reduced demand from gardeners and for irrigation, and on clay soils and in urban areas it caused some run-off to rivers that water companies have been able to pump into reservoirs. But in the ensuing hot weather, the soils have been drying out again.

So what is the answer? To transfer water from the reservoirs in the North-west? Before opting for this expensive solution, we should look back to the droughts of 1975-76 and 1984. The first affected all of southern Britain, but the West, relying on reservoirs, ran into more trouble than the East, with its aquifers.

The 1984 drought, which lasted only a few months, affected the usually wet North and West, as well as the South and East, where it was hardly noticed. From full capacity after a wet January, storage in many of the major reservoirs of Scotland, Wales and northern England was down to about 30 per cent by September, when significant rainfall occurred. Reservoirs, which are expensive to build, hold less water than aquifers and need to be replenished regularly. Even after the present drought, there is probably more usable water in the chalk than in all the reservoirs in England and Wales combined. But those who use it to supply the public are vilified by many for causing the disappearance of wetlands.

As the climate gets wetter, there is also a tendency for rainfall to increase in winter and decrease in summer. These trends are in line with, though do not necessarily confirm, the predictions of global warming. While water resources will benefit generally, the country will be increasingly vulnerable to the rogue years that defy the statistics, leaving us with an exceptionally dry winter in between the drier summers.

For the present, the water situation in south-east England remains rather like the economy - severely depressed, and in serious danger of getting worse before it gets better.

Michael Price is a Senior Lecturer in Hydrogeology at the University of Reading.

(Photograph omitted)

Start your day with The Independent, sign up for daily news emails
Arts and Entertainment
Attenborough with the primates
tvWhy BBC producers didn't want to broadcast Sir David Attenborough's famed Rwandan encounter
News
people
News
Campbell: ‘Sometimes you have to be economical with the truth’
newsFormer spin doctor says MPs should study tactics of leading sports figures like José Mourinho
News
news
ebooks
ebooksA special investigation by Andy McSmith
Voices
Lance Corporal Joshua Leakey VC
voicesBeware of imitations, but the words of the soldier awarded the Victoria Cross were the real thing, says DJ Taylor
Life and Style
Alexander McQueen's AW 2009/10 collection during Paris Fashion Week
fashionMeet the collaborators who helped create the late designer’s notorious spectacles
Sport
football
News
i100
News
Perry says: 'Psychiatrists give help because they need help. You would not be working in mental health if you didn't have a curiosity about how the mind works.'
people
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Recruitment Genius: Bookkeeper / Office Co-ordinator

£9 per hour: Recruitment Genius: This role is based within a small family run ...

Recruitment Genius: Designer - Print & Digital

£28000 - £32000 per annum: Recruitment Genius: This Design and marketing agenc...

Recruitment Genius: Quantity Surveyor

£46000 per annum: Recruitment Genius: This property investment firm are lookin...

Recruitment Genius: Telesales / Telemarketing Executive - OTE £30k / £35k plus

£18000 - £35000 per annum: Recruitment Genius: This company specialises provid...

Day In a Page

War with Isis: Fears that the looming battle for Mosul will unleash 'a million refugees'

The battle for Mosul will unleash 'a million refugees'

Aid agencies prepare for vast exodus following planned Iraqi offensive against the Isis-held city, reports Patrick Cockburn
Yvette Cooper: We can't lose the election. There's too much on the line

Yvette Cooper: We can't lose the election. There's too much on the line

The shadow Home Secretary on fighting radical Islam, protecting children, and why anyone in Labour who's thinking beyond May must 'sort themselves out'
A bad week for the Greens: Leader Natalie Bennett's 'car crash' radio interview is followed by Brighton council's failure to set a budget due to infighting

It's not easy being Green

After a bad week in which its leader had a public meltdown and its only city council couldn't agree on a budget vote, what next for the alternative party? It's over to Caroline Lucas to find out
Gorillas nearly missed: BBC producers didn't want to broadcast Sir David Attenborough's famed Rwandan encounter

Gorillas nearly missed

BBC producers didn't want to broadcast Sir David Attenborough's famed Rwandan encounter
Downton Abbey effect sees impoverished Italian nobles inspired to open their doors to paying guests for up to €650 a night

The Downton Abbey effect

Impoverished Italian nobles are opening their doors to paying guests, inspired by the TV drama
China's wild panda numbers have increased by 17% since 2003, new census reveals

China's wild panda numbers on the up

New census reveals 17% since 2003
Barbara Woodward: Britain's first female ambassador to China intends to forge strong links with the growing economic superpower

Our woman in Beijing builds a new relationship

Britain's first female ambassador to China intends to forge strong links with growing economic power
Courage is rare. True humility is even rarer. But the only British soldier to be awarded the Victoria Cross in Afghanistan has both

Courage is rare. True humility is even rarer

Beware of imitations, but the words of the soldier awarded the Victoria Cross were the real thing, says DJ Taylor
Alexander McQueen: The catwalk was a stage for the designer's astonishing and troubling vision

Alexander McQueen's astonishing vision

Ahead of a major retrospective, Alexander Fury talks to the collaborators who helped create the late designer's notorious spectacle
New BBC series savours half a century of food in Britain, from Vesta curries to nouvelle cuisine

Dinner through the decades

A new BBC series challenged Brandon Robshaw and his family to eat their way from the 1950s to the 1990s
Philippa Perry interview: The psychotherapist on McDonald's, fancy specs and meeting Grayson Perry on an evening course

Philippa Perry interview

The psychotherapist on McDonald's, fancy specs and meeting Grayson Perry on an evening course
Bill Granger recipes: Our chef recreates the exoticism of the Indonesian stir-fry

Bill Granger's Indonesian stir-fry recipes

Our chef was inspired by the south-east Asian cuisine he encountered as a teenager
Chelsea vs Tottenham: Harry Kane was at Wembley to see Spurs beat the Blues and win the Capital One Cup - now he's their great hope

Harry Kane interview

The striker was at Wembley to see Spurs beat the Blues and win the Capital One Cup - now he's their great hope
The Last Word: For the good of the game: why on earth don’t we leave Fifa?

Michael Calvin's Last Word

For the good of the game: why on earth don’t we leave Fifa?
HIV pill: Scientists hail discovery of 'game-changer' that cuts the risk of infection among gay men by 86%

Scientists hail daily pill that protects against HIV infection

Breakthrough in battle against global scourge – but will the NHS pay for it?