After the driest spell for almost 50 years, the UK is now being warned to expect flooding from thundery showers that will offer little relief from the drought. The flood alert follows days of extreme heat warnings and the official declaration of a drought after the longest nine-month dry spell since 1976. Meteorologists warned that downpours are the wrong kind of rain to tackle the drought and are more likely to lead to floods from water running off parched earth. The heatwave is forecast to break with a yellow warning for thunderstorms covering almost all of the UK on Monday, all of England and Wales on Tuesday and most of southern and eastern England on Wednesday. The Met Office warned of “torrential downpours and possible disruption” in some spots, adding that homes and businesses could be “flooded quickly” and buildings damaged by flood water. It also said power cuts were possible. The Environment Agency also warned that properties could flood and travel could be disrupted by surface water. John Curtin, the agency’s executive director of operations, tweeted that the UK was in “that twilight zone of having both flood and drought warnings”. He said: “Heavy thundery rain on parched and hard ground will lead to rapid runoff and heightened flood risk this week. But this will in no way correct weeks of dry weather so most of England will remain in drought.” Prof Hannah Cloke, an expert in hydrology at the University of Reading, said the forecast rain was “unlikely to be long lasting or widespread enough to make a big difference to some exceptionally low levels in reservoirs and rivers”. Dan Stroud, a forecaster at the Met Office, said: “We’re coming to the end of an extended, very hot spell, and the ground has been baked, so it’s extremely dry. The weather is breaking down into a mixture of heavy and thundery showers. “And rain from really intense downpours will be unable to soak into the baked ground quickly. It’s very difficult for the water to actually get in, because it has to force the air out of the soil. So dry ground gets very quickly overwhelmed, and we then get surface runoff.” Advertisement He added: “What we really need is a continuous period of light rain or drizzle just to gently re-wet the soil. Intense downpours are not exceptionally helpful. It’s going to take a lot of rain over an extended period to actually recharge the aquifers and reservoirs.” Stroud said “almost anywhere” was at risk of the impact thundery downpours early this week, but it was difficult to pinpoint exactly where. “Scotland and Northern Ireland were most at risk on Sunday. As we move into Monday the risk develops initially across Wales, and the south-west, and then more widely across England during the afternoon and into the evening.” Last week the University of Reading released video of a simple experiment involved three cups of water to show how parched ground is resistant to absorbing water, making flash floods more likely. Rob Thompson, who conducted the demonstration, said: “Dry, parched ground doesn’t let water in as effectively as already moist ground … because the soil is resisting water entering, the water sits on the surface, to run off down slopes or simply sit in a pool.” An official drought was declared in eight areas of England on Friday by the National Drought Group. Three water companies – Welsh Water, Southern Water, and South East Water – have imposed hosepipe bans, while Yorkshire Water has announced that a ban will start on 26 August and Thames Water is planning one in the coming weeks. Lincolnshire police confirmed a teenage boy died on Saturday after getting into difficulty in the sea at Skegness after temperatures reached more than 30C in some parts of England. A body was also found in a Doncaster lake on Saturday, following reports that a man in his 20s had got into difficulty in the water. Two men have been arrested on suspicion of arson after a fire broke out in Norfolk. Emergency services were called to Bawsey Country Park, near King’s Lynn, on Sunday at about 11.40am after a disposable barbecue was “thrown” into woodland causing a small fire, police said. Norfolk constabulary said two men, both 44 and from Boston in Lincolnshire, had been arrested on suspicion of arson and criminal damage and taken to King’s Lynn for questioning. In Scotland, customers were evacuated from a Tesco supermarket in Inverness after water poured in through the ceiling on Sunday afternoon. Videos posted on social media showed tiles on the ceiling falling and water pouring in, covering most of the floor in the supermarket. The area was affected by heavy thunderstorms and torrential rain for most of Sunday. A Tesco spokesperson, said on Sunday evening: “Our Inverness Inshes Extra store is temporarily closed while we assess some damage to the roof. We’re sorry for any inconvenience. We’re working to reopen as soon as possible.” A car park close to the supermarket, located in the Inshes retail park, was also flooded, as was a nearby Vue cinema.