Northern Australia's Green Break of Season (GBOS) dates and their relationship with pasture

Abstract

Across northern Australia's rangelands, livestock production depends heavily on rain-fed pastures that rely primarily on rainfall during the wet season months of October to April. Planning for the onset of pasture growth (called green cover onset) after the dry season enables graziers to set appropriate stocking rates based on the available fodder at the end of the previous growing season. This reduces costs and alleviates the strain on existing livestock. This study focuses on the 'green break of season' (GBOS) date, defined as the first occurrence of meaningful rainfall over a 3-day period after the dry season, and its relationship to the green cover onset. By utilising robust model-derived estimates and satellite observations of pasture growth at representative locations, we examine the relationship between the green cover onset and GBOS for various rainfall thresholds and find a strong linear relationship. Additionally, we investigate the historical or long-term 'green date', at which the GBOS reliably occurs in 70% of all years. We analyse the spatial distribution of green dates over northern Australia and examine how these dates are influenced by the phase of the El Niño-Southern Oscillation. Ultimately, our findings aim to assist producers and graziers in determining their "decision date" for better management of livestock and resources.