Abstract
Abstract. This study addresses the role of the atmospheric moisture budget in determining the onset and development of summer droughts over the North American Great Plains (GP) using two state-of-the-art reanalysis datasets. We identified zonal moisture advection as the main cause of severe tropospheric drying during the extreme droughts in the southern GP in 2011 and northern GP in 2012. For both events, the eastward advection of anomalously dry and warm air in the free troposphere in spring set the stage for summer drought. This led to a sharp drop in relative humidity above the boundary layer, enhancing dry entrainment and suppressing deep convection. Further breakdown of the zonal advection into dynamic (caused by circulation anomalies) and thermodynamic (caused by moisture anomalies) contributions reveals dominance of thermodynamic advection in the tropospheric drying observed during the onset of both 2011 and 2012 droughts. The dependence of thermodynamic advection on the moisture gradient links springtime precipitation in the Rockies and southwestern US, the source region of the anomalous dry advection, to the GP summer precipitation (with correlations > 0.4 using gauge-based data). Identifying this previously overlooked precursor of the GP summer droughts improves our predictive understanding of drought onset mechanisms over the region.
Highlights
The United States (US) Great Plains (GP) are prone to devastating droughts such as the infamous Dust Bowl of the 1930s (e.g., Brönnimann et al, 2009; Donat et al, 2016), the extended drought in the 1950s (e.g., Cook et al, 2011), the Texas drought of 2011 (e.g., Fernando et al, 2016), and the record-breaking drought of 2012 (e.g., Hoerling et al, 2013)
The temporal evolution of the 2011 drought shows a steady decline of precipitation and ET starting in February, extending throughout the spring and peaking during summer (−2 mm d−1) in both MERRA2 and ERA-Interim reanalysis data (Fig. 2a and b)
To investigate the GP summer droughts from a moisture budget perspective, we looked at the individual moisture tendencies, their vertical structure, annual cycle, and diurnal variability for both the 2011 and 2012 events compared with the 1979–2018 climatology in ERA-Interim
Summary
The United States (US) Great Plains (GP) are prone to devastating droughts such as the infamous Dust Bowl of the 1930s (e.g., Brönnimann et al, 2009; Donat et al, 2016), the extended drought in the 1950s (e.g., Cook et al, 2011), the Texas drought of 2011 (e.g., Fernando et al, 2016), and the record-breaking drought of 2012 (e.g., Hoerling et al, 2013). Numerous studies have shown that, in the early stages of the GP droughts, the upper-level atmosphere features an anomalous high and anticyclonic vorticity over central North America (Chang and Wallace, 1987; Namias, 1991; Lyon and Dole, 1995; Cook et al, 2011; Donat et al, 2016; Fernando et al, 2016). A dynamical teleconnection between the height anomalies over the US and the North Pacific sea surface temperature (SST) anomalies has been considered as the main driver responsible for the onset of GP summer droughts in 1980 and 1988 (Trenberth et al, 1988; Lyon and Dole, 1995; Chen and Newman, 1998).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
