大兴安岭林区10小时时滞可燃物湿度的模拟

随着森林防火预报精细化的需求,小时尺度可燃物湿度的准确模拟成为火险预报的关键。利用2010年8月连续无降雨天气条件下我国大兴安岭林区10h时滞可燃物湿度和相应气象因子的半小时动态观测资料,从可燃物的失水和吸水过程对目前广泛使用的Fosberg模型和Van Wagner模型进行评估,进而发展了准确模拟10h时滞可燃物失水和吸水过程的可燃物湿度模型。结果表明:Fosberg模型对10h时滞可燃物的失水过程模拟较好(R²=0.96,P<0.01),而Van Wagner模型对10h时滞可燃物的吸水过程模拟较好(R²=0.83,P<0.01),但均不能独立地准确模拟10h时滞可燃物的湿度变化。通过分析可燃物失水与吸水过程,考虑可燃物在静风条件下的水汽交换,优化了Van Wagner模型参数,建立了综合反映可燃物失水与吸水过程的10h时滞可燃物湿度模型。据比较,该模型可准确地模拟10h时滞可燃物的湿度变化(R²=0.88,P<0.01),可为精细化火险预报提供技术支撑。

Simulating 10-hour time-lag fuel moisture in Daxinganling

Wildfire is a necessary disturbance for forest ecosystem's regeneration and succession, but frequent and large fires threaten human life and activities. Forecasting forest fires is a useful method for fire disaster prevention and emergency operation. The accurate simulation of moisture content of dead fuels is critical for forest fire danger forecast because it's strongly related to the ignition and fire spread. Daxinganling provides many forestry productions to China but it was also one of the highly fire-prone areas in China. Developing an accurate model for estimating hour scale dead fuel moisture content in the Daxinganling is very necessary and important. A fire remote automatic weather station was settled in Huzhong National Nature Reserve which is located in the Daxinganling larch forest to collect 10-hour time-lag fuel moisture content and meteorological factors (temperature, relative humidity and wind speed). The record frequency is half-hour per time. In this research, Fosberg model and Van Wagner model were evaluated, since they were widely used in forest fire danger forecast system and based on the equilibrium moisture content (EMC) that is easy to use. Desorption and absorption processes are the key to simulate fuel moisture content. So, this research chooses continuous observation data during August 25-28, 2010 without any precipitation to validate these two processes. The results show that both Fosberg model and Van Wagner model can simulate when desorption or absorption process begins, but all of them could not simulate well for whole process independently. Fosberg model could give better simulation at desorption stage (R²=0.96, P<0.01), and Van Wagner model does better at absorption stage (R²=0.83, P<0.01). Through analysis the potential actual variation of fuel moisture content in the desorption and absorption process, the vapour exchange coefficient is nearly to be a constant in the desorption which is coincide with Fosberg model's and the absorption's the vapour exchange coefficient seem to be variable which is similar to the Van Wagner model's. Thus, a new hour scale fuel moisture model is developed considering the difference of desorption and absorption processes: the desorption process based on Fosberg model with the Simard's EMC model and the absorption process based on Van Wagner model with the Van Wagner's EMC model. The new model use the difference between fuel moisture content and Van Wagner's absorption EMC to determine the vapor exchange process, and it could give better simulation (R²=0.77, P<0.01). But the absorption processes was underestimated in the calm weather, and the modified model simulated better (R²=0.88, P<0.01).This research could provide the technical supports for the forest fire danger forecast in Daxinganling.