A report into why people start forest and grass fires has found that boredom is one of the main reasons.
The investigation, by Forestry Commission Wales, also found that socio-economic factor were also to blame and that some started fires for “fun”.
Between 2000 and 2008 there were more than 55,000 grassfires and nearly 550 forest fires recorded in South Wales – eight times more than in other similar areas of the United Kingdom.
Deliberate wildfires cost the fire service £7 million a year to fight.
Publication of the 107-page report, which was written by social scientist Matthew Jollands, follows one of the worst periods of wildfires in Wales, when thousands of hectares of forest were lost to arson attacks during March and April.
Mr Jollands spent two years analysing the social, environmental and economic factors that motivate people to start fires.
The report said wildfires followed a predictable pattern every year and found that the 20% most deprived areas of South Wales were nine times more likely to suffer than the 20% least deprived areas, with the Rhondda and Afan Valleys most prone to wildfire arson.
Peter Cloke, Forestry Commission Wales deputy district manager in South Wales, also worked on the report.
He said: “By identifying the causes and understanding why people commit these wanton acts of destruction, we hope it will enable more effective policies to be designed to tackle wildfire arson.
“The insights provided by the report and the recommendations on how to combat wildfire arson throughout South Wales, whether within land management policy and practice or in how organisations interact with affected communities, point the way forward for everybody with an interest in looking after our countryside.”
Over 60% of wildfires happen between 4pm and midnight with Sunday being the most popular day for setting fires (18%). Most fires occur in March and April (44%).
Over 1,000 residents of South Wales were surveyed and 65% believed wildfires were deliberately started, with youngsters regarded as the main culprits – though farmers or land owners are more likely to be blamed in south-west Wales.
However, although South Wales is the worst place in the UK for wildfires, only 33% of respondents felt the area had a problem and fewer still (18%) believed wildfires were a problem in their local area.
The report has recommended that partnership working between organisations, such as the recent Project Bernie, is key to combating the problem.