A Live Fuel Moisture Climatology in California

The average wildfire size in California has continuously been growing larger each year. This poses health and safety risks to the surrounding populous. Since the live fuels affects fire risk, flammability, and rate of spread, an analysis of the live fuel moisture climatology is important to understand recent fire trends. In this study we analyzed the observations of the main live fuel types in eight different regions in California from 2000-2021. To gather the necessary live fuel moisture content (LFMC) data, we created a database called the Fuel Moisture Repository which collects data from the National Fuel Moisture Database, stores it in a practical and organized way on a local machine, and allows users to query specific data. We analyzed the most frequently sampled fuel type in each of the eight regions and found high variability in LFMC across investigated fuel types. The regions were split between having up trending and down trending LFMC. Whether or not the regions saw a downtrend or uptrend in their LFMC, a shorter time between the maximum and minimum moisture contents in each of the regions that were observed indicating an extension of the length of fire season. The analysis of drought conditions revealed that the variability in LFMC across all the regions was related to water deficit. Drought conditions appeared to be different in each region we examined and seemed to be one of the causes of extreme variability in LFMC. During extended drought periods, it was also seen that the fuels adapted to their environmental conditions and would stabilize or even increase their maximum and minimum moisture values instead of seeing continual decreases. An analysis of the fire activity data was combined with the LFMC data to define local thresholds indicating an onset of large fire potential. Although our analysis confirmed previously published live fuel moisture threshold for large fire occurrence in the Los Angeles region (79%), careful examination of other regions proved that each region had a different cortical LFMC threshold, ranging from 69% to 99%.