Abstract:

[Objective] Temperature is an important factor affecting fuel moisture and is frequently used for fuel moisture prediction. Fuel surface temperature is used in physical or quasi-physical moisture models instead of air temperature, thus, a conversion from air temperature to fuel surface temperature is required. Currently commonly used conversion models such as Byram & Jemison mdoeland Van Wagner model are statistically based models with varied applicability at different regions. In this study, we intend to answer following questions: 1) What are differences between air temperature and fuel surface temperature at different areas? 2) How about the applicability of these conversion models at different regions? 3) What is the deviation of fuel moisture prediction using these conversion models? [Method] Air temperatures at 1.5 m height in a Korean pine stand and a larch stand were measured using a automatically weather station in Maoershan Forest Farm in Harbin, Heilongjiang Province. The fuel surface temperatures at 1, 2, 3 and 4 cm above ground surface were measured at the same time using thermocouples. Temperature observation was conducted for ten days in the Korean pine stand and four days in the larch stand. Moisture contents of the fuels at 1 cm above surface ground were monitored at 1h intervals at two sites in each stand for a successive 24 h. Comparison of air temperature and fuel surface temperature at different heights were conducted. Deviation of fuel surface temperature computed using the two conversion models was evaluated. Applicability of the two models was assessed based on the deviation. Influences of conversion of fuel surface temperature from air temperature using the two models on direct estimation accuracy of fuel moisture via a model proposed by Catchpole et al. were evaluated. [Result] 1) There exist differences between air temperature and fuel temperature, that is, fuel temperature is lower than air temperature in daytime but higher at night. 2) The two conversion models have deviation of more than 3℃, however it cannot reflect the bidirectional differences of air temperature and fuel temperature at daytime and night. 3) Models for direct estimation of fuel moisture established using air temperature and using fuel temperature calculated from the two conversion models have similar accuracy. [Conclusion] Temperature computed from the two conversion models is higher than the measured values in field with much greater deviation, indicating that temperature conversion is not suitable in this study area. It is not necessary to convert air temperature to fuel temperature, but using air temperature directly at 1h intervals for direct estimation of fuel moisture. It can still not determine which one is better to establish fuel moisture mode by using air temperature or fuel surface temperature and further investigation is required. Another important task for future research is developing new temperature conversion models which can truly reflect daily differences between air temperature and fuel surface temperature.

Key words: fuel temperature, air temperature, fuel moisture, direct estimation, maoershan forest Farm