Indian and Pacific Ocean Influences on Southeast Australian Drought and Soil Moisture

Abstract

The relative influences of Indian and Pacific Ocean modes of variability on Australian rainfall and soil moisture are investigated for seasonal, interannual, and decadal time scales. For the period 1900-2006, observations, reanalysis products, and hindcasts of soil moisture during the cool season (June-October) are used to assess the impacts of El Niñ o-Southern Oscillation (ENSO) and the Indian Ocean dipole (IOD) on southeastern Australia and the Murray-Darling Basin, two regions that have recently suffered severe droughts. A distinct asymmetry is found in the impacts of the opposite phases of both ENSO and IOD on Australian rainfall and soil moisture. There are significant differences between the dominant drivers of drought at interannual and decadal time scales. On interannual time scales, both ENSO and the IOD modify southeastern Australian soil moisture, with the driest (wettest) conditions over the southeast and more broadly over large parts of Australia occurring during years when an El Niñ o and a positive IOD event (La Niñ a and a negative IOD event) co-occur. The atmospheric circulation associated with these responses is discussed. Lower-frequency variability over southeastern Australia, however, including multiyear drought periods, seems to be more robustly related to Indian Ocean temperatures than Pacific conditions. The frequencies of both positive and negative IOD events are significantly different during periods of prolonged drought compared to extended periods of ''normal'' rainfall. In contrast, the frequency of ENSO events remains largely unchanged during prolonged dry and wet periods. For the Murray-Darling Basin, there appears to be a significant influence by La Niñ a and both positive and negative IOD events. In particular, La Niñ a plays a much more prominent role than for more southern regions, especially on interannual time scales and during prolonged wet periods. For prolonged dry (wet) periods, positive IOD events also occur in unusually high (low) numbers.

Decadal-scale teleconnection between South Atlantic SST and southeast Australia surface air temperature in austral summer

“…Many previous studies have linked Australian climate to various large-scale remote climate drivers (Risbey et al 2009;Ummenhofer et al 2011;Hunter and Binyamin 2012;Fierro and Leslie 2014), and most of these studies focused on rainfall variability. The El Niño-Southern Oscillation (ENSO) (Taschetto and England 2009;Cai et al 2011;Ummenhofer et al 2011), Indian Ocean Dipole (IOD) (Risbey et al 2009;Cai et al 2011), Southern Hemisphere annular mode (SAM) (Hendon et al 2007;Meneghini et al 2007;Risbey et al 2009;Feng et al 2010a), sea surface temperature (SST) in the Wharton Basin (Li et al 2012a) and monsoon-like Southwest Australian circulation (SWAC) (Feng et al 2010b(Feng et al , 2015Li et al 2011) are all reported to modulate Australian rainfall on interannual time scales.…”

The influence of boreal winter extratropical North Pacific Oscillation on Australian spring rainfall

“…Maximum rainfall occurred along the southeastern and eastern coast, as well as the northern and southwestern coast, decreasing far inland. Previous studies demonstrated that Australian spring rainfall is influenced by many factors, such as the El Niño-Southern Oscillation (ENSO) (e.g., McBride and Nicholls 1983;Ropelewski and Halpert 1987;Nicholls et al 1996;Chiew et al 1998;Taschetto and England 2009), the Indian Ocean dipole (e.g., Saji et al 1999;Ashok et al 2003;Ummenhofer et al 2011), and the Antarctic Oscillation or southern annular mode (e.g., Gong and Wang 1999;Thompson and Wallace 2000;Marshall 2003;Hendon et al 2007). For example, studies find that Australian rainfall tends to be below average during El Niño events and above average during La Niña events, especially across the eastern two-thirds of the Australian continent during austral spring (e.g., Allan 1988;Wang and Hendon 2007).…”

A synoptic climatology of heavy rain events in the Lake Eyre and Lake Frome catchments

“…The degree of saturation of this sub-surface layer appears to act as a low pass filter on the catchment precipitation in a similar way to the finding of Ummenhofer et al (2011). This property could possibly be employed in future attempts to predict lake levels following periods of heavy rain.…”