Connection between low soil moisture and wildfire intensity

The connection between low soil moisture and wildfire intensity is well established and involves several interacting factors related to fuel availability, fuel moisture, and fire behavior:

• Low soil moisture leads to drier vegetation and fuels, which increases their flammability and the likelihood of ignition and rapid fire spread. When soil moisture is low, plants experience water stress, leading to drying and curing of live and dead fuels, which can accelerate fire intensity and size41113.

• Soil moisture influences wildfire size differently across seasons and vegetation types. During the growing season, low soil moisture is strongly linked to larger wildfires because it reduces fuel moisture and accelerates curing, making fuels more combustible. In dormant seasons, soil moisture is less predictive of fire size, especially in grasslands where dead fuel moisture is less dependent on soil moisture31113.

• Pre-season soil moisture conditions affect wildfire occurrence and burned area. Wet conditions before fire season promote biomass growth, increasing fuel availability, but if followed by dry conditions during fire season, this can lead to large, intense fires. Conversely, dry pre-season soil moisture tends to correlate with fewer but larger fires due to limited fuel accumulation but higher flammability59.

• Soil moisture affects fire-promoting vegetation conditions more than temperature at large scales, controlling both biomass growth (fuel availability) and vegetation moisture content (flammability). This dual role varies by climate: in arid regions, soil moisture mainly controls biomass growth, while in humid regions, it mainly affects vegetation moisture and flammability29.

• Wildfire severity and soil properties: Wildfires increase soil bulk density and reduce soil moisture retention, which can exacerbate drying and fuel flammability post-fire, potentially influencing subsequent fire behavior110.

• Soil moisture data improves wildfire risk prediction. Incorporating soil moisture measurements enhances fire danger assessments beyond traditional indices based on temperature and humidity alone, allowing earlier and more accurate predictions of fire probability and intensity4111215.

In summary, low soil moisture reduces fuel moisture content and accelerates fuel curing, which significantly increases wildfire intensity and size, especially during the growing season. Pre-season soil moisture also modulates fuel availability, influencing fire occurrence and severity. These relationships vary by vegetation type and climate but are fundamental to understanding and predicting wildfire dynamics3591116.

1. https://lfs-mlws-2020.sites.olt.ubc.ca/files/2021/10/Cheng-2021-A-Review-of-Wildfire-Effects-on-Soils-Hydrologic-Processes-and-Water.pdf
2. https://www.nature.com/articles/s41598-020-67530-4
3. https://acsess.onlinelibrary.wiley.com/doi/full/10.2136/sssaj2015.01.0041
4. https://nwfirescience.org/sites/default/files/publications/WF22056.pdf
5. https://pmc.ncbi.nlm.nih.gov/articles/PMC5822439/
6. https://www.sciencedirect.com/science/article/abs/pii/S0378112721004679
7. https://ntrs.nasa.gov/api/citations/20190027471/downloads/20190027471.pdf
8. https://www.drought.gov/sectors/wildfire-management
9. https://pmc.ncbi.nlm.nih.gov/articles/PMC7335103/
10. https://www.nature.com/articles/s41561-024-01563-6
11. https://ntrs.nasa.gov/api/citations/20230014040/downloads/IJWF%20Accepted_Manuscript.pdf
12. https://www.drought.gov/news/using-soil-moisture-information-better-understand-and-predict-wildfire-danger-2023-03-09
13. https://www.climatehubs.usda.gov/sites/default/files/Ochsner_Soil_Moisture.pdf
14. https://appliedsciences.nasa.gov/what-we-do/projects/evaluating-role-soil-moisture-determining-vegetation-health-fuel-loads-and
15. https://www.fws.gov/project/using-regional-soil-moisture-map-wildfire-probability
16. https://doaj.org/article/1599ce98c9374241ac4e20f06e37082f
17. https://www.sciencedirect.com/science/article/abs/pii/S0022169414005332
18. https://www.mdpi.com/2072-4292/16/13/2457
19. https://pubmed.ncbi.nlm.nih.gov/32620812/
20. https://www.publish.csiro.au/wf/fulltext/WF22056