Examining multi-scale atmospheric processes and land-atmosphere interactions associated with drought over the western U. S. in 2021-2022

Drought has a major impact on regional water supplies and is influenced by meteorological features at various spatial scales. For the last several years, the western United States has been experiencing drought conditions, notably during the winter of 2021-2022. A better understanding of the mechanisms influencing the ongoing drought is required to best prepare for the future effects of the Western drought through improved drought forecasts. Since drought conditions are mainly influenced by synoptic scale features and land-surface interactions, these effects warrant further examination. To analyze synoptic features associated with the drought conditions, monthly composite anomalies of surface pressure, 500 mb geopotential height, outgoing longwave radiation (OLR), temperature, and monthly composites of surface pressure and 500 mb winds from NOAA’s Physical Science Laboratory were collected. The data represent two separate time periods: September 2021 through August 2022 and September 2018 through August 2019. These were drought and non-drought years, respectively. The composites indicate stronger ridging and high-pressure patterns in winter 2022 compared to 2019, leading to reduced cloud cover indicated by positive OLR anomalies, which was determined to be the main driver of the event at the synoptic scale. To analyze the effects of the land-atmosphere interaction, level two soil moisture retrievals from the soil moisture active-passive (SMAP) satellite were obtained for the same time periods as the composite maps. From these data, daily averages of soil moisture observations for four regions across the United States were taken and the time series were plotted. The different regions were selected based on drought conditions in 2019 and 2022 as well as typical soil moisture levels. The results show that western regions experienced drier soils during the winter and early spring of 2022 than during the same time period in 2019. Continued research will focus on other variables related to land-atmosphere interactions, including the depth of the boundary layer, lifted condensation level height, and convective available potential energy. The regional analysis will be conducted using the mesoscale community Weather Research and Forecasting (WRF) model, which will be used to study the connection between the different variables and understand the processes of drought evolution.