Establishing Relationships between Drought and Wildfire Danger Indices for Improved Wildfire Risk Management

Despite a clear link between drought and wildfire, there is currently a lack of information for stakeholders at the regional and local levels for improved wildfire risk management using drought early warning information. Fire managers and other specialized fire professionals, such as Incident Meteorologists, will increasingly need to effectively use drought information in forecasts of fire behavior at fire incidents, and in long-term fuel management planning (e.g., for prescribed fire treatments) as the climate continues to warm along with shifts in the timing and duration of fire seasons. This project builds upon the current National Integrated Drought Information System (NIDIS) California-Nevada Drought Early Warning System (DEWS) through development of enhanced visualization and analysis tools, and establishment of a stronger and more direct link between drought early warning and wildfire danger information. Common drought indices (e.g., the Palmer Drought Severity Index [PDSI]; the Standardized Precipitation Index [SPI]) are used by Predictive Services, an interagency group that provides decision-support information needed to be more proactive in anticipating significant fire activity and determining resource allocation needs, and to inform monthly and seasonal significant wildfire potential outlooks. However, other potentially relevant drought indices have yet to be fully considered (e.g., the Evaporative Demand Drought Index [EDDI]; the Standardized Precipitation Evapotranspiration Index [SPEI]). In this study PDSI, SPI, SPEI, and EDDI were compared to two fire danger indices: the Energy Release Component (ERC), which reflects the contribution of live and dead fuels to fire intensity, and the 1000-hour fuel moisture, which indicates the moisture content in dead fuels three to eight inches in diameter. Analysis was conducted spatially over California and Nevada predictive service areas. Drought indices were lag-correlated to monthly (June-September) fire danger indices using several time scales (SPI, SPEI, and EDDI are all multiscalar) to identify potential wildfire risk early warning. Results indicate that EDDI and SPEI typically have stronger correlations (r^2 > 0.70) to ERC and 1000-hr fuel than do PDSI and SPI. This highlights the importance of evaporative demand on fire danger during the summer months in California and Nevada regions that have a pronounced dry season. In general, lag-correlations revealed minimal predictive capability of drought indices beyond lags of 0 months, with the exception of June where stronger correlations were found out to lags of 3 months.