There are some people that studied these fenomenon better than I actually did. So I took the information from a specialized agriculture site. http://www.afrol.com/Countries/Gambia/backgr_landuse.htm
"...Bushfires are in general caused by human activities, and are ignited deliberately or accidentally. Deliberately ignited fires are set to prepare new agricultural land, fertilize agricultural land or to kill or drive away pest animals, such as insects, bush pigs, snakes, parasites, etc. These fires, however, often get out of control and devastate large areas. Most fires, though, are probably ignited accidentally, caused by cigarettes, cooking fires, etc. Bush fires are believed to burn about 80% of the bush annually..."
The Gambia Major Gambian Land Use Zones-www.afrol.com)
This is the view of a farm while the sun goes down.
Usually people live inside hosues with all their family members. there is no such thing of wach in each house.