Synoptic-dynamical view of droughts in the southern Murray-Darling Basin of Australia

Australia is a country prone to drought and has experienced several severe droughts in its recent history. Most studies have linked large-scale modes of variability to Australian droughts, whereas few studies investigate droughts from the perspective of weather systems. In the current study, a wide range of weather systems (cyclones, anticyclones, fronts, warm conveyor belts, potential vorticity streamers, and cut-off lows) are investigated in association with heavy rainfall days that are important to meteorological drought in the southern Murray-Darling Basin. Two distinct phases (development and recovery) of drought are identified based on the standardised precipitation index.

This study shows that heavy rainfall days produce less rain during the development phase of drought in the southern Murray-Darling Basin, compared to the recovery phase. The rainfall reduction in the development phases is mainly due to a reduction in the frequency and intensity of rainfall associated with warm conveyor belts. On heavy rainfall days, warm conveyor belts are less frequent and weaker in their strength in the vicinity of the southern Murray-Darling Basin during drought development, whereas they are more frequent, intense, and persistent over this region during recovery from drought. Moreover, the spatiotemporal evolution of rainfall is consistent with the ascending branch of warm conveyor belts, supporting the importance of warm conveyor belts to rainfall.

Regarding the source of moisture on heavy rainfall, there is a notable decrease in moisture transport over the Coral Sea during the development of drought, whereas strong moisture divergence is identified in this region during the recovery phase.