The autumn break for cropping in southeast Australia: trends, synoptic influences and impacts on wheat yield

Abstract

ABSTRACT:The autumn break is the first significant rainfall event of the winter growing season. Two definitions of the autumn break have been developed for northwestern Victoria; a so-called ideal break and a minimum rainfall condition for sowing a wheat crop termed a minimal break. Application of the ideal break definition for an eight-station average reveals that 41 autumn breaks occurred in the first half of the record and 34 in the second half ) with a trend towards breaks occurring later in the season. In the decade to 2006, there have been only 3 ideal breaks (1999, 2000 and 2005) and none of the selected rainfall stations has recorded an 'extreme' wet autumn over the last 11 years, the longest period recorded for this criterion. A synoptic analysis for the period 1956-2006 has established that breaks are predominantly associated with systems known as cutoff lows. The influence of these systems has varied markedly throughout the analysis period and only one autumn break has been caused by a cutoff low in the final decade of the analysis. Additionally, the total rainfall associated with cutoff lows in the April to June period has declined significantly over the past 30 years.A farming system model has been employed to simulate a wheat crop in northwestern Victoria under historical conditions for a range of management options. Average yield across all years of the simulation declines with delay in the sowing date after late April, but there is a marked interannual variability in yield response to the sowing date which is related to rainfall distribution in the growing season in each year. The simulated in-crop rainfall indicates that the most recent drought in southeastern Australia is comparable in severity with the two major droughts in the 20th Century.

Towards understanding hydroclimatic change in Victoria, Australia – preliminary insights into the "Big Dry"

“…This trend is consistent across all nine study catchments and supports the findings of numerous previous studies (e.g. CSIRO, 2008;Murphy and Timbal, 2008;Potter et al, 2008, and publications produced as part of the SEACI (www.mdbc.gov.au/ subs/seaci)). This reduction in streamflow has also been accompanied by a reduction in rainfall as shown in Fig.…”

“…3 that the majority of the decrease in annual rainfall since 1994 is due to a large reduction in autumn (and to a lesser degree winter and spring) rainfall -this finding supports the results of several previous studies (e.g. Murphy and Timbal, 2008;Pook et al, 2008;Cai and Cowan, 2008a, b). Importantly, not only is there an obvious decrease in median rainfall, the extremely wet autumn rainfall totals that occurred in pre-1994 have not occurred post-1993.…”

“…This demonstrates that the mid-1990s climate shift is not unprecedented, at least in terms of significant changes from wet to dry epochs across Victoria -this finding is supported by previous studies into SEA hydroclimatology (e.g. Watkins, 2005;CSIRO, 2008;Murphy and Timbal, 2008;Potter et al, 2008;Verdon-Kidd and Kiem, 2009b) Figure 3 illustrates the seasonality of the mid-1990s climate shift by showing the seasonal rainfall totals for the periods 1948 to 1993 (the most recent "wet" epoch) and 1994 to 2007 for the nine study catchments. It is evident from Fig.…”

“…Many studies (e.g. Cai and Cowan, 2008a, b;CSIRO, 2008;Murphy and Timbal, 2008;Pook et al, 2008;Potter et al, 2008, and publications produced as part of the SEA Climate Initiative (SEACI; www.mdbc.gov.au/subs/ seaci)) have pointed out that the majority (∼60%) of the total Correspondence to: A. S. Kiem (anthony.kiem@newcastle.edu.au) SEA annual rainfall decline is due to drier autumns (MarchMay), which is the crucial season for "wetting up" Victorian catchments so as to ensure satisfactory streamflow throughout the rest of the year (Pook et al, 2008). The dynamics behind the SEA rainfall decline are still highly uncertain (e.g.…”

Trends in synoptic circulation and precipitation in the Snowy Mountains region, Australia, in the period 1958–2012

“…Studies from North America and Europe indicate hydroclimate changes associated with warmer temperatures and increasing precipitation intensity will have ongoing implications for water policy and society (Hoy et al 2014;Gillies et al 2012). Upward trends in extreme rainfall intensity in the Mediterranean are adversely affecting soil erosion with associated risks for flash flooding (Vallebona et al 2014), whilst changes in precipitation regimes can affect the timing and success of crop production (Stocker et al 2013;Pook et al 2009). Alpine areas are particularly vulnerable to climate change and its impact on their hydroclimate (Beniston 2003).…”