New models simulate how smoke moves at night
In southern America, most controlled burning takes place during the first three months of the year, a time when the needs of human populations and forest ecologies can come into visible - and sometimes deadly - conflict.
Forest Service researchers are testing desktop modelling programs to provide forest managers the real-time information they need to reduce the impact of smoke from prescribed burning.
Prescribed burning - the deliberate setting of fires under controlled conditions -is used to treat some 6 to 8 million acres in southern US states each year. About half this area is burned for forest management, the remainder for agricultural and range purposes. Southern land managers recognise prescribed burning as the most economical way to reduce the risk of wildfires and to maintain habitat for fire-dependent plant and animal species.
Prescribed burning is increasingly limited by air quality concerns in the south, where urbanisation continues to grow and major highways snake through forested areas. Thick smoke, especially when mixed with late night or early morning fog, can reduce visibility to zero and create extremely treacherous driving conditions. Keeping smoke away from highways is further complicated by the highly variable nature of the weather during the burning season in the south.
Dr. Gary Achtemeier, meteorologist with the Southern Research Station of the USDA Forest Service, recently presented results from testing two modelling programs designed to simulate the movement of night smoke resulting from prescribed burning.
'Simulating smoke at night is a very complex problem,' said Achtemeier, who leads the Southern Research Station's Smoke Management Team in Athens, Georgia. 'Shifts in the wind can carry smoke to different locations at various times during the same night. You can't really use wind information from nearby weather stations because they usually report wind speeds of less than two miles per hour as calm. A wind blowing at two miles per hour for ten hours can actually move smoke 20 miles from its origin point, potentially affecting road visibility at many locations and at great distances.'
The two Prescribed Burn (PB) models, PB-Piedmont and PB-Coastal Plain, are designed to run on laptop computers at faster-than-real-time. PB-Piedmont simulates the movement of night wind as it drifts through the shallow gaps in ridges and down road and stream cuts of the Piedmont, while PB-Coastal Plain tracks smoke movement over the flat Coastal Plain and nearby water surfaces.
Both PB-Piedmont and PB-Coastal Plain are simplified models designed for the specific weather conditions that occur when smoke is trapped close to the ground. The models are currently connected with hourly weather forecasts and can predict smoke movement in a range of about half an hour.
'We consider our current versions 'nowcast' rather than 'forecast' models,' said Achtemeier. ' We plan to connect the PB models with the high resolution weather prediction models being developed by the Southern High Resolution Modelling Consortium. This will increase the predictive range of the models to 48 hours or longer.' Although the models are performing as designed, Achtemeier cautions that further validation studies must be done before they can be fully adopted by forest and land managers.