Subseasonal Meteorological Drought Development over the Central United States during Spring

Bor-Ting Jong

NRC Post Doc, NOAA Physical Sciences Lab

Tuesday, Jun 22, 2021, 2:00 pm
Webinar

Abstract

Rapidly evolving flash droughts in the spring season (April-June), such as the 2012 Great Plains drought, are among the most devastating natural hazards in North America due to their severe impacts on agricultural productions. Yet, comprehensive characteristics and predictability of springtime flash droughts in the central U.S. are less studied. This talk will present common aspects of the evolution of springtime subseasonal “meteorological droughts”, here defined as persistent precipitation minus evaporation (P-E) deficits, using JRA-55 reanalysis data for the years 1958-2018. On average, these droughts in the central U.S. are initiated by a quasi-stationary Rossby wave packet (RWP), propagating from the western North Pacific. The RWPs induce persistent P-E deficits mainly through strong subsidence and the resulting low-level divergent outflow, which dries the atmosphere and drives moisture out of the region. The consequent “dynamically driven” increase in evaporative demand corresponds to a rapid drying of the root-zone soil moisture reservoir, which decreases ~40 percentiles within ~10 days. The resulting soil moisture deficit then lingers a month or more, especially in late spring. Our composite analysis, based upon strong and persistent P-E deficits, capture much of the springtime development of flash droughts in the central U.S.