Met Office analysis suggests that the UK could experience a 1976-style drought every 10 years, and the Environment Agency said that with the population of London and the South East set to grow by 23% by 2035, action should be taken now.
Modelling suggests some river flows could be cut by up to 80% during the summer in the next 40 years as the climate changes, putting more pressure on businesses that rely on taking water from rivers for irrigation.
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Nabi Tajima, who was the last known person to have been born in the 19th century, died in Japan after being in hospital since January.
Temperatures are predicted to reach a high of 23C.
Hunt accused companies of "turning a blind eye" to a generation of children "exposed to harmful emotional side effects" of social media.