Did the ‘Millennium Drought’ ever end?

Ailie Gallant¹, Sophie Lewis² 

1. School of Earth, Atmosphere and Environment, Monash University, VIC, Australia
2. School of Physical Environmental and Mathematical Sciences, University of New South Wales, Canberra, ACT, Australia

The Millennium Drought was a persistent and prolonged dry period that dominated the climate of southeast Australia during the first decade of the 21^st century. Beginning around 1997, the Millennium Drought was predominantly characterised by the lack of autumn and winter precipitation interspersed with several dry springs and summers that culminated in seasonal-scale periods of acute drought (e.g. 2002/03, 2005/06). Another unique characteristic compared to past decadal-scale droughts was that there was an absence of any months with above-average precipitation in some regions. It is widely accepted that the Millennium Drought ended abruptly with the onset of strong La Niña conditions in 2010.

However, we show evidence that despite the high precipitation in the spring and summer of 2010, the anomalously dry conditions in autumn and winter have continued and are not markedly different to the conditions observed during the Millennium Drought. Specifically, below or near average precipitation in these seasons persists and there have been no years with well above average precipitation, which is unusual in the observational record. This raises the question of whether the Millennium Drought ended, or whether it was just interrupted by the 2010 La Niña. Moreover, we show that the characteristics of the autumn/winter precipitation decline in the southeast is remarkably similar to the characteristics of the winter decline in southwest Western Australia that have been observed since the mid-1970s. These dry conditions in the southwest Western Australia winter months are now entering their fourth decade and continue. Therefore, it is imperative to first establish whether the Millennium Drought is ongoing and ultimately, what the underlying causes are for these ongoing dry conditions.

Identifying Drought Resilience in Eastern Australia

Abraham J Gibson¹, Danielle C Verdon-Kidd¹, Gregory R Hancock¹ 

1. University of Newcastle, Callaghan, NSW, Australia

A key focus of developing effective drought management practices is maintenance and protection of resources during periods of climate stress, and promoting quick recovery when relief occurs; i.e. being resilient to drought. Anecdotal evidence suggest that some regions of Australia are more ‘drought resilient’ than others.  One of these regions is the high rainfall zone of eastern Australia (i.e. east of the Great Dividing Range), which displays a lower degree of interannual climate variability than west of the divide. However, to determine which regions are most resilient requires quantification of drought propagation throughout a catchment, and, the subsequent catchment response and recovery. Therefore, this study aims to measure the response to drought of two agricultural catchments in the eastern Australia high rainfall zone. The analyses are underpinned by the Scaling and Assimilation of Soil Moisture And Streamflow (SASMAS) field-measured soil moisture dataset and remote sensed vegetation data. It is shown that during drought periods vegetation stress increased while soil moisture declined, however, both recovered quickly and displayed small variation between drought and non-drought periods. As a result, the catchments may be considered resilient to drought; with specific catchment characteristics playing a role in this. The study diversifies traditional approaches to studying droughts by quantifying catchment response to drought. This highlights the potential to use similar techniques to better understand drought resilience in other catchments in Australia and globally. This is a key step towards better drought management and reducing the impacts of drought globally.

Are Australia’s Major Southern Cities Increasingly Vulnerable to Drought?

Joshua Hartigan¹, Shev MacNamara¹, Lance M Leslie¹ 

1. University of Technology Sydney, Ultimo, NSW, Australia

Publish consent withheld

The contribution of ocean variability to Australian Megadroughts and Megapluvials

Andrea S Taschetto¹, Alex Sen Gupta¹, Caroline C Ummenhofer² 

1. Climate Change Research Centre, University of New South Wales, Sydney, NSW, Australia
2. Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, MA, USA

Australian precipitation is strongly affected by ocean-atmosphere modes of variability, such as the El Niño – Southern Oscillation (ENSO), and by internal atmospheric modes, e.g. the Southern Annular Mode (SAM). In this study we investigate the contribution of the sea surface temperature (SST) interannual to multidecadal variability for Australian precipitation, and examine to what extent internal atmospheric variability can generate extended periods of drought. Multi-century simulations are integrated using the National Center for Atmospheric Research (NCAR) Community Earth System Model (CESM) model. Three experiments are performed: (i) a fully coupled climate system run, (ii) a run forced with a climatological cycle of SST, i.e. no SST variability beyond one year, and (iii) a run forced with monthly and inter annually varying SST, i.e. containing SST variability but no air-sea feedback.

Results show that year-to-year variations in SST enhance rainfall variability and extremes, thus generating more severe droughts and wet spells compared to a world without interannual ocean variations. We also found that ENSO is a crucial phenomenon for resetting droughts and pluvials. In the fully-coupled climate system simulation, dry and wet spells are more likely to have a 3-yr duration. However, in the absence of ocean variability (i.e. in a world with no ENSO) droughts and pluvials generated by internal atmosphere variability can last longer, as there is no ENSO event to terminate extended dry or wet periods.