The significant increase in the number of forest fires has raised great interest in studying ways to decrease this number and optimization is one of the most used techniques. This type of methods allows the support of the combat means in fighting forest fires, improving the effectiveness and speed of the firefighters actions. Knowing how many and which resources to allocate to each fire is an important key to success in extinguishing ignitions. Thus, this paper presents a resource dispatch problem for forest firefighting, where 7 resources are assigned to 20 fires at different instants of time. The main objective is to minimize the total amount of water used to extinguish all ignitions. For this, a genetic algorithm adapted to this problem was used. A statistical analysis between several population sizes of GA was performed to identify the one that allow to obtain the best results for this problem.