How Oceanic Oscillation Drives Soil Moisture Variations over Mainland Australia: An Analysis of 32 Years of Satellite Observations*

Abstract

Australia is frequently subject to droughts and floods. Its hydrology is strongly connected to oceanic and atmospheric oscillations (climate modes) such as the El Niño-Southern Oscillation (ENSO), Indian Ocean dipole (IOD), and southern annular mode (SAM). A global 32-yr dataset of remotely sensed surface soil moisture (SSM) was used to examine hydrological variations in mainland Australia for the period 1978-2010. Complex empirical orthogonal function (CEOF) analysis was applied to extract independent signals and to investigate their relationships to climate modes. The annual cycle signal represented 46.3% of the total variance and a low but highly significant connection with SAM was found. Two multiannual signals with a lesser share in total variance (6.3% and 4.2%) were identified. The first one had an unstable period of 2-5 yr and reflected an east-west pattern that can be associated with ENSO and SAM but not with IOD. The second one, a 1-to 5-yr oscillation, formed a dipole pattern between the west and north and can be linked to ENSO and IOD. As expected, relationships with ENSO were found throughout the year and are especially strong during southern spring and summer in the east and north. Somewhat unexpectedly, SAM impacts strongest in the north and east during summer and is proposed as the key driver of the annual SSM signal. The IOD explains SSM variations in the north, east, and southeast during spring and also in the west during winter.

State of the Climate in 2016

“…ENSO anomalies are known to potentially cause continental deviations in terrestrial water storages (Bauer-Marschallinger et al 2013;Boening et al 2012;Miralles et al 2014a of El Niño (Dorigo et al 2016). Instead, globally and for both hemispheres, average soil moisture was slightly above normal in 2016 ( Fig.…”

State of the Climate in 2014

“…ENSO anomalies have the potential to cause continent-wide deviations in terrestrial soil moisture and total water storage ( Bauer-Marschallinger et al 2013;Boening et al 2012;De Jeu et al 2011, 2012bMiralles et al 2014b). ENSO-driven global negative soil moisture anomalies are particularly visible during the 1997-98 El Niño, while positive anomalies are clearly observed for the strong La Niña episodes of 1999-2000 and 2010-11, particularly for the Southern Hemisphere.…”

State of the Climate in 2013

“…These areas are particularly sensitive to drought during the El Niño phase of ENSO ( Bauer-Marschallinger et al 2013;Miralles et al 2014). Anomalous dry conditions were observed in particular in the Southern Hemisphere, e.g., in Argentina, northeastern Brazil, southern Africa, and Australia.…”