"I am less worried about the climate change story in northern Europe, where higher temperatures and CO2 are likely to increase productivity," he said. "Of much greater concern is the uncertainty around rainfall. You could get 50 per cent more or less than the norm in a given summer," while a winter drought such as experienced in parts of the country in 2011-12 "can be worse than a summer one", he added.
"You can't sustain yields and quality while relying on uncertain rainfall, so don't ignore that part of your business," he urged. "Start factoring in how you will deal with drought and waterlogging because these are both likely to become more frequent and intense."
Knox pointed out that according to projections for changing climate: "By 2050, land well-suited to potato growing in England will have all but disappeared."
Already half of all abstraction licence holders are in over-abstracted areas "as we tend to grow crops on drier land", he said. "It's a worrying starting point for abstraction reform." In plans currently under discussion, future licences will be based on six-year aggregate permitted volumes. "It's a big challenge and will have a big impact on investment," he added. "You need to have good data on past water use because that will be the basis of future licences."
Knox, who is also director of the UK Irrigation Association, suggested that growers in clusters such as West Sussex "should look at how much water they need for a twoto three-week period and build a shared reservoir for that rather than working independently".
Paul Dracott, manager of the WATERR project based at East Malling Research (EMR) helping growers in the South East to use water more efficiently, said: "We have to face the reality of more expensive water. Efficient irrigation is one of the best ways to improve productivity. There is a three-fold difference in water-use efficiency between good and bad substrate strawberry growers.
"The top quartile get 50 per cent more yield and make seven per cent more per kilogram than the bottom quartile. Water use is a major factor in best practice - it's something staff need more training in." A "UK Centre for Water Efficient Technology" is being planned at EMR as a resource for growers, Dracott added.