Wildfires can be detrimental to urban and rural communities, causing impacts in the form of psychological stress, direct physical injury, and smoke-related morbidity and mortality. This study examined the area burned by wildfires over the entire state of California from the years 2000 to 2020 in order to quantify and identify whether burned area and fire frequency differed across Census tracts according to socioeconomic indicators over time. Wildfire data were obtained from the California Fire and Resource Assessment Program (FRAP) and National Interagency Fire Center (NIFC), while demographic data were obtained from the American Community Survey. Results showed a doubling in the number of Census tracts that experienced major wildfires and a near doubling in the number of people residing in wildfire-impacted Census tracts, mostly due to an over 23,000 acre/year increase in the area burned by wildfires over the last two decades. Census tracts with a higher fire frequency and burned area had lower proportions of minority groups on average. However, when considering Native American populations, a greater proportion resided in highly impacted Census tracts. Such Census tracts also had higher proportions of older residents. In general, high-impact Census tracts tended to have higher proportions of low-income residents and lower proportions of high-income residents, as well as lower median household incomes and home values. These findings are important to policymakers and state agencies as it relates to environmental justice and the allocation of resources before, during, and after wildfires in the state of California.

California’s Sierra Nevada has experienced a large increase in wildfire activities over recent decades. This intensifying fire regime has coincided with a warming climate and increasing human activity, but the relative importance of the biophysical and anthropogenic drivers of wildfire remains unclear across this diverse landscape, especially at a finer spatial scale. We used multisource geospatial data sets of fire occurrence, and human, climatic, and biophysical variables to examine the spatial pattern and controls on Sierra Nevada wildfires averaged from 1984 to 2017. The maximum entropy model driven by both biophysical and anthropogenic variables predicted the spatial distribution of fire probability well, with an area under the curve (AUC) score of 0.81. Model diagnostics revealed that aspects of the climate, including vapor pressure deficit (VPD), temperature, and burning index (difficulty of control), dominated the spatial patterns of fire probability across the whole Sierra Nevada region. The VPD was the leading control, with a relative contribution of 32.1%. Population density and fuel amount were also significant drivers, each accounting for 15.8%–12.4% of relative contribution. VPD and burning index were the most important factors for fire probability in higher elevation forest, while population density was comparatively more important in the lower elevation forest regions of the Sierra Nevada. Our findings improved our understanding of the relative importance of various factors in shaping the spatial patterns of historical fire probability in the Sierra Nevada and across various subecoregions, providing insights for targeting spatially varying forest management strategies to limit potential future increases in wildfires.

Satellite-based active fire (AF) products provide opportunities for constructing continuous fire progression maps, a critical data set needed for improved fire behavior modelling and fire management. This study aims to investigate the geospatial interpolation techniques in mapping daily fire progression and assess the accuracy of the derived maps from multi-sensor active fire products. We focused on 42 large wildfires greater than 5000 acres in Northern California from 2017 to 2018, where the USDA Forest Service National Infrared Operations (NIROPS) daily fire perimeters were available for comparison. The standard active fire products from the Moderate Resolution Imaging Spectroradiometer (MODIS), the Visible Infrared Imaging Radiometer Suite (VIIRS), and the combined products were used as inputs. We found that the estimated fire progression areas generated by the natural neighbor method with the combined MODIS and VIIRS active fire input layers performed the best, with R 2 of 0.7 ± 0.31 and RMSE of 1.25 ± 1.21 (10 3 acres) at a daily time scale; the accuracy was higher when assessed at a two day rolling window, e.g., R 2 of 0.83 ± 0.20 and RMSE of 0.74 ± 0.94 (10 3 acres). Relatively higher spatial accuracy was found using the 375m VIIRS active fire product as inputs, with a kappa score of 0.55 and an overall accuracy score of 0.59, when interpolated with the natural neighbor method. Furthermore, locational pixel-based comparison showed 61% matched to a single day, and an additional 25% explained within ±1 day of the estimation, revealing greater confidence in fire progression estimation at a 2-day moving time interval. This study demonstrated the efficacy and potential improvements of daily fire progression mapping at local and regional scales.

The capillary fringe is a poorly defined, tension‐saturated region with important influences on soil biogeochemistry. The goal of this research was to evaluate the effects of the capillary fringe moisture gradient on biogeochemical processes and to assess whether these processes are more similar to those of unsaturated or saturated zones. Effects were documented during 118 d using two soils with contrasting textures in laboratory mesocosms. A water table was maintained at a constant height, and the parameters measured included soil moisture, inorganic N, decomposition, and reduction changes. Moisture levels suggest that capillary rise occurred ≥22.5 cm above the water table in both soils. Although limited by experimental methods, including using homogenized and sieved soil materials, biogeochemical trends for all measured parameters were seen by depth and between soils and seem to be influenced by water content and O2 diffusion. Nitrate concentrations increased above the water table. Decomposition was lowest in and immediately above the saturated water table and greatest where moisture and O2 were balanced. Reducing conditions existed ≥10 cm above the water table in the sandy soil and ≥5 cm in the loamy soil, indicating that these regions share characteristics with the saturated zone. The sandy soil showed reduction higher above the water table than the loamy soil, possibly due to structural and O2 diffusion differences due to experimental methods. Specific heights of capillary fringe were not identified; instead, the data support a model of a continuous moisture content gradient in the capillary fringe between the water table and soil surface.

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