IT MAY surprise you, given the downpours we have seen over the past couple of weeks, to learn that we are facing “the prospect of the worst drought for 100 years in the South and South East”, according to Elliot Morley, the Minister of State for Climate Change and Environment. We have had a dry spring: Kent and Sussex received around two thirds of their average rainfall for April, while the Thames Valley and London fared even worse, receiving just over half the average rainfall.

For many people, such dry weather brings anxiety over the state of the garden. Eight water companies across the South East now have a full hosepipe and sprinkler ban, which means that 13 million people are unable to water the lawn or wash the car by hose. The Chelsea Flower Show, which begins on Tuesday, solved its problems by sinking a 100 metre-deep borehole. For the ordinary homeowner, this is a rather too expensive option.

Moreover, the real danger for homeowners is not a yellowing lawn or the ignominy of driving a dirty car. Drought brings with it a far worse threat: subsidence.

“Drought quite definitely has an effect on the incidence of subsidence,” Neil Curling, the senior manager of Halifax’s subsidence team, says. “Exceedingly dry weather brings a lot of extra damage.” Curling says that during the last very dry period in England — the summer of 2003 — subsidence claims rose by about a quarter. “During peak time for subsidence claims — from September to October — claims were double or even treble the usual level,” he adds.

Experts say that 2006 could be a particularly bad year for subsidence, with the Environment Agency predicting a record year for claims. But how do you know if your home is likely to be at risk? The answer is that if you live in the South East and if you have trees in close proximity to your home, subsidence is a real danger. “The vast majority of subsidence happens in houses built on clay soil,” Curling says. “

That’s predominantly London and the South East, although there is also a stretch along the east side of the country, and Bristol is also a hot spot.”

The major cause of subsidence is clay shrinkage, which happens as the ground dries up and is exacerbated by tree roots which suck moisture out of the soil. Although Curling says that the quickest way to avoid subsidence is to get rid of any trees that may be near your home, he concedes that for most people this is not a desirable option — and in cases where trees are protected it may not even be possible. “The trick is to manage the trees by reducing them before they cause a problem,” he says.

The trees you need to be concerned about are those closest to your house. If a tree is closer to the house than it is tall, you need to consider cutting it back. If a 10ft tree is 20ft away from your home, it is unlikely to cause any problems. If it is 5ft away, then it could be a threat. Curling says that the worst offenders when it comes to subsidence are large, broadleaf, thirsty trees such as willow, poplar and oak.

Do not think that you will be able to prevent subsidence by watering your garden frequently. “It is very unlikely that you would be able to get the volume of water that you would need,” Curling says. “Trees can drink thousands of gallons of water a day.” If you think your home may be at risk of subsidence, you need to keep a careful eye out for telltale signs. Cracks are a sign that the house may be moving, but not all cracks indicate something sinister. “What you will see is cracks from the corners of windows and door openings,” Curling says. “The dangerous cracks are those that are wider at one end than the other. Most cracks in the plaster have no width at all, but subsidence cracks are open.”

If you do have such problems, there is no need to panic. In many cases the problem can be dealt with fairly simply, the quickest way being to remove problem trees. Once you have done that, the ground will rehydrate gradually. “The cracks will often close up altogether, provided that bits of plaster or other debris have not fallen into them. Once the building is rehydrated and stable, it is a question of repair work — plastering and redecoration.”

Happily, underpinning — the strengthening and deepening of building foundations — is rarely required.

FACTFILE

In the most recent very hot summer, 2003, nearly 50,000 homes suffered problems from subsidence.

The typical cost of a subsidence claim is £8,000. Most homeowners will have to pay the first £1,000, although some policies have an excess of as much as £5,000.

For further advice, go to the Royal Institution of Chartered Surveyors website: www.rics.org. Other useful websites include: www.abi.org.uk, www.subsidence.org.uk, www.aviva.com

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