Fire services are urging people to not start deliberate fires after more than 500 grass and rubbish fire since March.
South Wales and Fire Rescue said it had been a 'busy' weekend for its crews dealing with the fires which are taking up vital resources and endangering lives.
Services are already stretched because of the coronavirus pandemic but deliberate fires mean resources are being diverted away from helping communities.
Firefighters have also warned that fire smoke irritates airways and can cause further issues for people with respiratory conditions.
Just last month, fire crews across Wales urged people to stop starting "illegal and irresponsible". North Wales Fire and Rescue Service issued a warning about deliberate fires following a spate of arson attacks across north Wales earlier in March.
The fire service have also warned against the use of sky lanterns following posts on social media encouraging releasing them to show support for the NHS.
It said, ''At time of increased pressure of all emergency services sky lanterns pose a significant fire hazard. Please use an alternative to show your support.''