Atypical influence of the 2007 La Niña on rainfall and temperature in southeastern Australia

Abstract

Interannual climate variations associated with El Niño – Southern Oscillation (ENSO) dominate rainfall and temperature variability in southeastern Australia's Murray‐Darling Basin (MDB), an important region for agricultural productivity. Following a decade‐long dry period, a La Niña during 2007 failed to provide above average rainfall and cool temperatures in the southern half of the MDB, typical of most La Niña events for the region. Instead, annual (winter half‐year) rainfall was 17% (35%) below average and maximum temperatures 0.91°C (1.26°C) above average. Based on the past variability between La Niña events, the combined probability of such anomalies is less than 2%. It is likely that these anomalies contain some contribution from a positive Indian Ocean Dipole (IOD). However, the IOD and other large‐scale circulation features are unlikely to explain the atypical conditions that occurred in the southern MDB during the 2007 La Niña.

Understanding hydroclimate processes in the Murray-Darling Basin for natural resources management

“…The rankings from Table 2 are also in agreement with and Verdon-Kidd and Kiem (2009b) who suggested that a consistently positive SAM since the 1990s, associated with a poleward retraction of the mid-latitude storm track (Frederiksen et al, 2011), may be responsible for the recent trends in southeast Australian rainfall. However, there are some conflicts between these results and other studies that show there are no significant associations between southeast Australian autumn rainfall and the SAM ).…”

“…3 and 4, which are very important (see later discussion). Further, longer term trends in some inter-annual processes have recently been identified including an increase in the intensity of the STR (Drosdowsky, 2005;Larsen and Nicholls, 2009;Williams and Stone, 2009) and a poleward retraction of the mid-latitude storm belt (Frederiksen et al, 2011) which is consistent with trends towards a more positive SAM (Marshall, 2003). As such, these trends have also been included and assessed in Table 2 as potential causal mechanisms of the Big Dry.…”

“…This can be overcome by continuing two major research streams. The first involves complementing the limited instrumental record (approximately 100 yr) by extending the historical record using various sources of palaeoclimate information (Verdon and Franks, 2006;Lough, 2007;Gallant and Gergis, 2011). Verdon and Franks (2006) estimated variations in east Australian rainfall using reconstructions of the PDO for the past 400 yr. More recently, Gallant and Gergis (2011) and Gergis et al (2012) developed an experimental reconstruction of River Murray streamflow and southeast Australian rainfall, respectively, and showed that the streamflow deficits associated with the Big Dry were very rare, but not necessarily unprecedented during the period 1783-1988.…”

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

“…However, the maximum temperature anomaly is anomalously high (figure not shown). It therefore seems that the low probability of only 2% for the combined anomalies during a La Niñ a year (Gallant and Karoly 2009) is largely due to the maximum temperature, not the precipitation. However, it should be noted that the regions investigated do not completely coincide.…”

“…The only exception is September, when 70% of La Niñ as record above-average precipitation. Gallant and Karoly (2009) described unusual conditions over SEA during the La Niñ a of 2007, with winter rainfall 35% below average and maximum temperatures 1.268C above average. Based on past variability, they concluded that only 2% of La Niñ a events were likely to have this combined precipitation and temperature anomaly over the southern regions of the MDB and suggested modulating influences by the pIOD during 2007.…”