Key Points:

• Greater use of soil moisture information in fire danger rating systems could lead to earlier warning of wildfire danger, and better forecasts of wildfire occurrence and size.
• Soil moisture data sources are increasingly available at temporal and spatial scales needed to support fire danger assessment, including in situ and remotely-sensed datasets as well as data derived from improved land surface modeling.  
• Findings from diverse ecosystems and geographies highlight the dependencies of fuel loads, fuel moisture content, and wildfire probability on soil moisture.
• Soil moisture has been found to be a strong predictor of live fuel moisture, and more recently of dead fuel moisture of forest litter.
• Although the relationships between soil moisture levels and live and dead fuel moisture and fuel loads can vary by ecological type (e.g., forests versus grasslands), researchers have made strides in characterizing these differences.
• Because current soil moisture conditions can influence future fuel load, soil moisture observations may be particularly helpful in providing forecasts of wildfire danger.