Observed land surface feedbacks on the Australian monsoon system

The current study investigates the observed land surface feedbacks on the Australian monsoon system by applying a multivariate statistical method, Stepwise Generalized Equilibrium Feedback Assessment (SGEFA), to a spectrum of observational, remote sensing, and reanalysis datasets. In particular, the influence of Madden Julian Oscillation (MJO) on the Australian monsoon system is accounted for in the assessment of land surface feedbacks. The approach reveals the quantitative impacts and relative contribution of key individual oceanic, vegetation, and soil moisture forcings, along with the MJO, on the Australian monsoon’s observed sub-seasonal to interannual variability. During both the flanks and core of the Australian summer monsoon season, terrestrial and oceanic drivers impose comparable contributions, both exceeding MJO’s contribution, to the regional climate variability. Vegetation and soil moisture generally exert opposing feedbacks on the monsoon system, thereby weakening the net impact of terrestrial drivers. Vegetation feedbacks peak in the mid- to post-monsoon period, with positive anomalies in leaf area index generating a modified atmospheric circulation pattern that reduces moisture advection and rainfall across northern Australia. Soil moisture feedbacks are most pronounced during the pre- and post-monsoon seasons, with positive soil moisture anomalies favoring more rainfall through enhanced moisture recycling and modified atmospheric circulation. The current observational evidence of a negative vegetation-rainfall feedback across northern Australia and its underlying dynamical feedback mechanism deviates from most previous modeling studies that concluded a positive vegetation-rainfall feedback via a moisture recycling mechanism.