Geoscience Reference
In-Depth Information
Rainfall Decile Ranges
Highest in
period
Very much
above average
Above average
10
8-9
Average
4-7
Below avarage
Very much
below avarage
2-3
1
Lowest in
period
Rainfall Deciles (AWA grids 1900-2009)
1 September 1996 to 31 August 2009
Distribution based on gridded data
Product of the National Climate Centre
-
Commonwealth of Australia 2013, Australian Bureau of Meteorology
ID code: KJMap/WAPDeciles
Issued: 25/03/13
Figure 3.6
Rainfall deciles for the period 1 September 1996 to 31 August 2009
Source: Bureau of Meteorology (Australia)
Notes
a Deciles are calculated with respect to the 1900-2009 period.
b South-eastern and south-western parts of the continent experienced driest on record
conditions during this period.
Very high year-to-year and decade-to-decade rainfall variability, and an
association between rainfall and the El Niño-Southern Oscillation over large
parts of the continent, mean that periods of extended drought are common on
the mainland, interspersed by occasional periods of very heavy rainfall (Power et
al., 1998; 1999).
Changes to the duration and severity of drought periods can be characterized
as changes in local climate extremes. In this context, the noteworthy changes in
rainfall that have occurred across south western and south eastern parts of the
continent (
Figure 3.6
)
have likely impacted on the severity of episodic drought.
In the south west, the rainfall changes have been characterized by a seasonal
decline in winter rainfall of around 15 per cent since 1970, as well as an absence
of very wet years altogether. In the south east, similar declines in autumn and
early winter rainfall have occurred since 1996, with a similar absence of wet years
ended abruptly by heavy spring and summer rainfall in 2010/2011.
To date, many studies have noted the possible impact of both the timing
of rainfall changes and of highest on record temperatures on recent periods of
extended rainfall deficits, with the tendency toward amplification of hydrological
drought. In particular, autumn and winter rainfall deficits (of around 10-20
