Among the many impacts of the COVID-19, the pandemic has led to improved air quality conditions in the countries under quarantine. Satellite-based maps highlight a remarkable reduction in aerosol and air pollution due to the shutdown of industries and very limited traffic in China and other Asian countries between late January and March 2020. Similarly, many areas across the United States have also experienced a large reduction in air pollution due to the lockdown in response to COVID-19. Meanwhile, large areas of the central United States, particularly within the Missouri River Basin, received less precipitation than normal during February-April 2020. Is it possible that the observed reduction in precipitation was driven by the reduced aerosols due to the coronavirus? If so, how much of these changes can be attributed to the pandemic and what does it mean in terms of discharge?

Our hypothesis is that the local aerosol reduction led to a detectable change in precipitation and discharge across the central United State and Iowa, and that these effects were either magnified or reduced depending on the magnitude of the long-range transport of particles. Therefore, the goal of this proposal is to evaluate how much of an impact this abrupt reduction in local and remote aerosols played during the past winter/spring in terms of precipitation and discharge, and to determine the physical mechanisms at play.

The research methodologies build on analytical tools and data sets with which the research team has extensive experience, and will be developed further to address the role of the reduction in aerosols due to COVID-19 in relation to the reduced precipitation and discharge across the central United States broadly, and Iowa in particular.

We will use the Weather Research and Forecasting (WRF) model coupled with Chemistry version 3.8.1 (WRF-Chem), and force it with the North American Regional Reanalysis (NARR) data and the near real-time Whole Atmosphere Community Climate Model (WACCM) outputs. We propose to design four experiments to isolate the relative contribution of the aerosols: Control (CTRL), Business-as-usual (BAU), NoTrans, and NoLocal experiments. In these runs, the circulation (e.g., zonal and meridional winds, geopotential height) is the same but they have different settings for transported and local aerosols. By comparing the four experiments, we can assess the relative roles of aerosols in forcing the observed changes in precipitation and discharge during February-April 2020. In addition to precipitation and discharge, the proposed experiments will produce outputs (e.g., temperature, humidity, ultraviolet radiation, ozone) which are important to diagnose the environmental conditions for the survival and spread of COVID-19.

The proposed research will enhance our knowledge of the role of local and remote aerosols on precipitation and discharge across the central United States, with a special focus on Iowa. Given the extreme reduction in aerosols due to the pandemic, our findings will have both short- and long-term impacts. In the short term, insights gained from this research can provide information in terms of preparation for the upcoming fall and winter from the perspective of water resources and emergency management. In the long term, our work will provide basic information on the potential impacts of different mitigation efforts aimed at reducing anthropogenic aerosols on precipitation across the central U.S.

The results and data from this project will be made available to federal and state agencies. Moreover, this information will be readily available to local stakeholders and users for their own use. The research team will leverage the tools and expertise provided by the Iowa Flood Center (IFC) to make the results of the proposed work relevant and immediately and directly available to agencies and to the general public. Moreover, the dissemination of the results will be facilitated by means of outreach activities through the IFC and the Iowa Water Center.