Smoke‐Driven Changes in Photosynthetically Active Radiation During the U.S. Agricultural Growing Season

Abstract

Wildfire smoke is frequently present over the U.S. during the agricultural growing season and will likely increase with climate change. Studies of smoke impacts have largely focused on air quality and human health; however, understanding smoke's impact on photosynthetically active radiation (PAR) is essential for predicting how smoke affects plant growth. We compare surface shortwave irradiance and diffuse fraction (DF) on smoke‐impacted and smoke‐free days from 2006 to 2020 using data from multifilter rotating shadowband radiometers at 10 U.S. Department of Agriculture UV‐B Monitoring and Research Program stations and smoke plume locations from operational satellite products. On average, 20% of growing season days are smoke‐impacted, but smoke prevalence increases over time (r = 0.60, p < 0.05). Smoke presence peaks in the mid to late growing season (i.e., July, August), particularly over the northern Rocky Mountains, Great Plains, and Midwest. We find an increase in the distribution of PAR DF on smoke‐impacted days, with larger increases at lower cloud fractions. On clear‐sky days, daily average PAR DF increases by 10 percentage points when smoke is present. Spectral analysis of clear‐sky days shows smoke increases DF (average: +45%) and decreases total irradiance (average: −6%) across all six wavelengths measured from 368 to 870 nm. Optical depth measurements from ground and satellite observations both indicate that spectral DF increases and total spectral irradiance decreases with increasing smoke plume optical depth. Our analysis provides a foundation for understanding smoke's impact on PAR, which carries implications for agricultural crop productivity under a changing climate.

Variable impact of wildfire smoke on ecosystem metabolic rates in lakes

“…Smoke effects on ecosystem metabolic rates (i.e., GPP or R) have rarely been measured, despite the increased exposure of ecosystems to high-density smoke 3 . To date, studies of smoke impacts on ecosystems focus primarily on the effects of altered radiation uxes to forest or cropland production [10][11][12] , or on the effects of aerosol deposition on phytoplankton growth in oligotrophic marine systems 6,13,14 . Existing studies of smoke effects on inland waters are limited to single site case studies (e.g., Castle Lake 8, 15 ; Lake Tahoe 16 ) or focus on relatively few response variables (e.g., water temperature 7 , cyanobacterial blooms 17 ).…”

Variable impact of wildfire smoke on ecosystem metabolic rates in lakes

“…Smoke effects on ecosystem metabolic rates (i.e., GPP or R) have rarely been measured, despite the increased exposure of ecosystems to high-density smoke 3 . To date, studies of smoke impacts on ecosystems focus primarily on the effects of altered radiation fluxes to forest or cropland production [10][11][12] , or on the effects of aerosol deposition on phytoplankton growth in oligotrophic marine systems 6,13,14 . Existing studies of smoke effects on inland waters are limited to single site case studies (e.g., Castle Lake 8,15 ; Lake Tahoe 16 ) or focus on relatively few response variables (e.g., water temperature 7 , cyanobacterial blooms 17 ).…”

Wildfire smoke reduces lake ecosystem metabolic rates unequally across a trophic gradient

“…Smoke effects on ecosystem metabolic rates (i.e., GPP or R) have rarely been measured, despite the increased exposure of ecosystems to highdensity smoke 3 . To date, studies of smoke impacts on ecosystems focus primarily on the effects of altered radiation fluxes to forest or cropland production [10][11][12] , or on the effects of aerosol deposition on phytoplankton growth in oligotrophic marine systems 6,13,14 . Existing studies of smoke effects on inland waters are limited to single-site case studies (e.g., Castle Lake 8,15 ; Lake Tahoe 16 ) or focus on relatively few response variables (e.g., water temperature 7 , cyanobacterial blooms 17 ).…”