Developing a live fuel moisture model for moorland fire danger rating

Fuel moisture plays a crucial role in determining fuel flammability and fire behaviour but most models of fire hazard only refer to dead fuel assuming that it is the most important component driving fire behaviour. In a number of fuel types, particularly shrublands such as Calluna-dominated heathlands, live fuels can form a significant or even dominant proportion of the total available fuel. Understanding variation in their moisture content is a crucial first step in developing a robust fire danger rating system. An existing system based on the CWFIS has been implemented for the UK but does not perform well for shrub fuels. Live Calluna does not always follow obvious patterns of variation in FMC with particularly low values encountered in spring in cold or freezing conditions. We review the need for and development of a fire danger rating system and the role of live fuel moisture. We describe the first stages in the development of a physiological model that accounts for seasonal variation in leaf conductance, water viscosity, freezing conditions and rates of water uptake.