Relative Contributions of Local and Nonlocal Land–Atmosphere Feedbacks to the Evolution of Flash Drought and Implications for Predictability

Flash droughts are characterized by unusually rapid onset and intensification, and can have detrimental impacts to agriculture and water resources in a short period of time. Predicting and preparing for these events is especially challenging due to the accelerated timescale by which flash droughts develop and propagate. Land-atmosphere feedbacks have been shown to play a role in long term drought intensification, and may also play a key role in the behavior of flash drought. Dry soils over drought impacted regions can modify the moisture and temperature characteristics of an air mass which can perpetuate drought locally, but can also have impacts downstream through persistent advection of drought-modified air masses that increase evaporative demand over a region that is not already experiencing drought. This research uses kinematic backward trajectories derived from the North American Regional Reanalysis (NARR) to determine the origin of air masses residing over regions where flash drought developed. The selected flash drought cases were identified using an objective identification framework that also relies on data from the NARR. Multiple parcels within the atmospheric column at every grid point within the region impacted by flash drought were traced backward in time for a period of one pentad. Parcel moisture characteristics and land surface conditions were recorded along the path of the parcel at 3-hourly intervals. Trajectories were computed for the impacted region during the two pentads immediately preceding the onset of flash drought, and two pentads immediately following onset to evaluate the relative contributions of local versus non-local feedbacks throughout the development and intensification of flash drought.