Record Regional Rainfall Linked to COVID-Induced Aerosol Emissions Reduction
Tiny particles suspended in the air, or aerosols, have long been recognized as an important factor that can affect clouds, air and moisture movement, and rainfall. Because of the complex nature of the involved processes, the role of aerosols in climate change and extreme weather remains very uncertain. Researchers used the Department of Energy’s (DOE) Energy Exascale Earth System Model (E3SM) to reveal that the COVID-induced abrupt emissions reductions made a critical contribution to the summer 2020 record rainfall and flooding over eastern China. In climate model experiments, the dramatic aerosol reductions affected atmospheric heating and regional meteorological conditions, resulting in more moisture, which increases rainfall.
E3SM has a comprehensive, advanced representation of aerosols in the climate system. Researchers used its capabilities to conduct model experiments to quantify the impact of aerosol reductions on recent record rainfall in China and tease out underlying mechanisms. Their findings reveal an important role of aerosols in modifying regional weather conditions and extreme events. The findings have important implications for improving the prediction of climate responses to dramatic changes in aerosols. They motivate the need to improve the modeling of aerosol-cloud-precipitation processes and their impacts on the water cycle and extreme weather and hydrologic events.
A 60-year record for summer precipitation occurred over eastern China in 2020, when human activities and aerosol emissions were dramatically reduced. This study investigates the impact of abrupt, COVID-induced emissions reductions on the unprecedented summer precipitation using E3SM, other community climate model experiments, and observational datasets. Model experiments contrasted meteorological conditions, including regional total precipitation, between business-as-usual emissions and pandemic-induced reduced emissions. Experiments show that pandemic-induced aerosol reductions are a crucial factor in enhancing the prolonged summer precipitation over eastern China. This explains about one-third of the observed increase in 2020 rainfall relative to the 60-year average, although the magnitude of the precipitation response varies among the different climate models. The profound impact of the abrupt emissions reductions is different from previous reports of the climate system’s response to continuous but gradual emissions reductions. This study underscores the changes in atmospheric convection and large-scale circulation due to the COVID-induced aerosol reductions. Ongoing relevant E3SM work focuses on understanding how the effects of human-induced regional and global aerosol emissions changes depend on the historical climate, natural climate variability, and future warming climate.
This research used the National Energy Research Scientific Computing Center, a Department of Energy Office of Science User Facility, resources.