Droughts are associated with large‐scale modes of variability, synoptic‐scale systems, and
terrestrial processes. Quantifying their relative roles in influencing drought guides process understanding,
helps identify weaknesses in climate models, and focuses model improvements. Using a Lagrangian
back‐trajectory approach we provide the first quantification of the change in moisture supply during major
droughts in southeast Australia, including the causes of the changes. Drought onset and intensification were
driven by reduced moisture supply from the ocean, as moisture was circulated away from the region,
combined with an absence of precipitation‐generating mechanisms over land. During termination,
strengthened moist easterly flows from the Tasman and Coral Seas promoted anomalously high rainfall. Our
approach reveals terrestrial moisture sources played a secondary role, amplifying rainfall anomalies by
less than 6%. Simulating droughts therefore requires deeper understanding of the relationship between
moisture advection and synoptic‐scale circulation and how large‐scale climate variability and terrestrial
processes modify these relationships.
Figure 2. Moisture source anomalies during drought (a–d) onset, (e–h) intensification, and (i–l) termination in the northern region overlain by low‐level wind
speed anomalies. Droughts A, B, and C are represented in the top three rows, with the bottom row showing their mean.
This page is maintained by Jason Evans |
Last updated 23 January 2018