Agricultural Fallowing Drives Extreme Anthropogenic Dust and Visibility Degradation During the October 2021 Dust Event in California’s Central Valley

Yang Yu , Shu-Hua Chen, Adeyemi A Adebiyi , Md Minhazul Kibria, Satyendra Pandey

Anthropogenic dust aerosols from agricultural land affect regional air quality, visibility, and radiation, yet they are often ignored in atmospheric models. Here, we investigate the role of fallow croplands in driving anthropogenic dust emissions during the October 11, 2021, wind-driven dust event over California’s Central Valley (CV). The simulation without fallow croplands fails to reproduce the dust event, whereas the simulation including fallow-induced erodibility produces 90 t of dust emissions, reproducing the observed aerosol optical depth of 0.6-0.8 and PM10 concentrations of 1000-1200 µg m-3. Fallow-land-emitted dust reduces surface net radiation by 30 W m-2, leading to near-surface cooling of 0.2 ℃ and degraded visibility up to 1000 m. These results highlight the important role of agricultural fallowing in regulating regional dust emissions, particularly as climate-driven drought and groundwater sustainability policy are projected to substantially expand fallowed cropland areas across the CV in the coming decades.