Monitoring the Impacts of Wildfires on Forest Ecosystems and Public Health in the Exo-Urban Environment Using High-Resolution Satellite Aerosol Products from the Visible Infrared Imaging Radiometer Suite (VIIRS)

Abstract

Increasing development of exo-urban environments and the spread of urbanization into forested areas is making humans and forest ecosystems more susceptible to the risks associated with wildfires. Larger and more damaging wildfires are having a negative impact on forest ecosystem services, and smoke from wildfires adversely affects the public health of people living in exo-urban environments. Satellite aerosol measurements are valuable tools that can track the evolution of wildfires and monitor the transport of smoke plumes. Operational users, such as air quality forecasters and fire management officials, can use satellite observations to complement ground-based and aircraft measurements of wildfire activity. To date, wildfire applications of satellite aerosol products, such as aerosol optical depth (AOD), have been limited by the relatively coarse resolution of available AOD data. However, the new Visible Infrared Imaging Radiometer Suite (VIIRS) instrument on the Suomi National Polar-orbiting Partnership (S-NPP) satellite has high-resolution AOD that is ideally suited to monitoring wildfire impacts on the exo-urban scale. Two AOD products are available from VIIRS: the 750-m × 750-m nadir resolution Intermediate Product (IP) and the 6-km × 6-km resolution Environmental Data Record product, which is aggregated from IP measurements. True color (red, green, and blue [RGB]) imagery and a smoke mask at 750-m × 750-m resolution are also available from VIIRS as decision aids for wildfire applications; they serve as counterparts to AOD measurements by providing visible information about areas of smoke in the atmosphere. To meet the needs of operational users, who do not have time to process raw data files and need access to VIIRS products in near-real time (NRT), VIIRS AOD and RGB NRT imagery are available from the Infusing satellite Data into Environmental Applications (IDEA) web site. A key feature of IDEA is an interactive visualization tool that allows users to display tailored combinations of AOD and RGB imagery, as well as overlay the VIIRS smoke mask and fire hotspots at pixel resolution (~750-m × 750-m), and zoom into the county level. Two case studies of recent wildfires in the Western US are presented to show how operational users can access and display VIIRS aerosol products to monitor the transport of smoke plumes and evolution of fires in the exo-urban environment on the regional and county scales. The new National Oceanic and Atmospheric Administration (NOAA) Western Region Fire and Smoke Initiative is also discussed, which will enhance IDEA to allow visualization of VIIRS aerosol products down to the neighborhood scale. The new high-resolution VIIRS aerosol products can be used for NRT monitoring of human exposure to smoke, and they can be used to gauge the spread of fires and, thus, provide advanced warning for evacuations and fire suppression efforts, thereby reducing risks to human populations and forest ecosystems in the exo-urban environment.

Keywords: aerosols; air quality; atmosphere; remote sensing; urbanization; wildfires.

Figure 1

Annual cost of wildfire suppression in the US by the federal government in billions of dollars.

Figure 2

US EPA’s air quality index (AQI). The AQI is a dimensionless, color-coded scale that communicates the relative hazards of ambient air pollutants, including O₃ and PM_2.5.

Figure 3

Comparison of Collection 5 MODIS AOD (left) and VIIRS EDR AOD (right), showing areas of high AOD associated with a smoke plume across southern Iowa and northern Missouri on September 25, 2012. For this event, the smoke plume was captured at the edge of the scan for both MODIS and VIIRS. Pixel sizes grow in size at the edge of the scan by a factor of four for MODIS (to 40-km × 40-km) and by a factor of two for VIIRS (to 12-km × 12-km). The higher-resolution VIIRS EDR AOD product captures the variations in the density of the smoke plume (red, orange, and yellow colors), which are not resolved by the MODIS AOD product.

Figure 4

Example of VIIRS interactive visualization tool on the IDEA web site for July 24, 2014, showing IP AOD and RGB imagery.

Figure 5

Map of northeastern Washington State showing locations of fire hotspots (red flames) and smoke plumes (gray shaded areas) associated with wildfires burning on August 10, 2014. Darker gray colors indicate thicker smoke plumes. The black circle indicates the location of the Carlton Complex fire. Small colored circles reflect the AQI scale and indicate 24-hour average PM_2.5 concentrations in µg/m³; note the Code Orange concentrations adjacent to the Carlton Complex fire. [Hotspots and smoke plume data courtesy of NOAA Hazard Mapping System Fire and Smoke Product; PM_2.5 concentration data courtesy of EPA AIRNow-Tech.]

Figure 6

(A) The left panel shows VIIRS true color (RGB) NRT imagery from the IDEA web site for northeastern Washington State and southern British Columbia on August 10, 2014. Fire hotspots identified by VIIRS are overlaid as small red dots. The approximate location of the Carlton Complex fire is indicated by a white circle. Smoke plumes from the many fires burning across North–Central Washington State are evident as gray features covering much of northeastern Washington and southern British Columbia. (b) The right panel shows VIIRS 6-km × 6-km resolution Environmental Data Record (EDR) aerosol optical depth (AOD) NRT imagery overlaid on VIIRS RGB imagery from the IDEA Web site for northeastern Washington State and southern British Columbia on August 10, 2014. The approximate location of the Carlton Complex fire is indicated by a white circle. Areas of high AOD, shown by the red, orange, and yellow colors, correspond to smoke from the wildfires burning across North–Central Washington and southern British Columbia.

Figure 7

Map of Southern California showing locations of fire hotspots (red flames) and smoke plumes (gray shaded areas) associated with wildfires burning in northern San Diego County on May 16, 2014. Darker gray colors indicate thicker smoke plumes. Small colored circles reflect the AQI scale and indicate 24-hour average PM_2.5 concentrations in µg/m³; note the Code Orange concentrations downwind (northeast) of the fires. [Hotspots and smoke plume data courtesy of NOAA Hazard Mapping System Fire and Smoke Product; PM_2.5 concentration data courtesy of EPA AIRNow-Tech.]

Figure 8

(A) The left panel shows VIIRS 750-m × 750-m resolution Intermediate Product (IP) aerosol optical depth (AOD) NRT imagery from the IDEA web site for Southern California on May 16, 2014. Areas of high AOD, shown by the red, orange, and yellow colors, north of San Diego, near Temecula, Oceanside, and Fallbrook correspond to smoke from the wildfires burning in northern San Diego County. Areas of high AOD over Los Angles are due to urban haze. (b) The right panel shows VIIRS true color (RGB) NRT imagery from the IDEA web site for Southern California on May 16, 2014. Fire hotspots identified by VIIRS are overlaid as small red dots. The pink shaded areas correspond to the VIIRS smoke mask. Smoke from the San Diego County wildfires is evident as a light gray feature in the RGB image, but it is difficult to discern. The pink VIIRS smoke dust mask captures the thickest parts of the smoke plume, aiding in identification and tracking.

Figure 9

VIIRS 750-m resolution Intermediate Product (IP) aerosol optical depth (AOD) on May 16, 2014, showing the full resolution (right panel) of the AOD data on the neighborhood scale for a community west of Temecula, CA. The scale of the right panel is 5-km × 5-km, with each square AOD pixel measuring 750-m × 750-m. Note that the AOD data are overlaid on a street map, illustrating the potential for tracking smoke plumes on the neighborhood scale.