One source of information about weather and climate that is particularly good is the Bureau of Meteorology website. For information about why Victoria had a very wet season recently (and the wettest summer on record), the Annual Climate Summary 2010 provides valuable information. Here is an excerpt:
Sea-surface temperatures (SSTs) in the Australian region were the highest on record during 2010, 0.54 C above average. SSTs were particularly high from autumn onwards with individual monthly SST records set during March, April, June, September, October, November and December. The most recent decade (2001-2010) was also the warmest decade on record with an anomaly (departure from average) of +0.33 C. Each of the last ten decades has been warmer than the preceding decade.
Early in the year, positive SST anomalies were generally located in southern Australian waters, however by March positive anomalies were becoming established in northern waters. Above-average SSTs were a feature of northern Australian waters for much of the year.
Along with a favourable hemispheric circulation associated with the 2010 La Nina, very high SSTs contributed to the record rainfall and very high humidity across eastern Australia during the second half of the year. For the months of October, November and December tropical SSTs broke previous records by large margins and occurred in regions that, historically, have a strong association with Australian rainfall. Waters off the northwest coast of Western Australia during November had an anomaly of +1.08 C, which was 0.30C above the previous record set in 1998.
When the surface of the sea is hotter, more water will evaporate and there will be more to fall as rain. The record wet filled many dams and caused widespread flooding, including flash floods all over and weeks long huge floods over western Victoria. Compare the effect of La Nina after the disastrous drought, with the low water level in the Hume Dam in previous years in the 2000s (almost none in 2009)
AFAIK, the most likely scenario for Victoria over the coming several decades is that it will continue to get hotter and drier - but when it's wet it will rain buckets - just like it did in the recent La Nina.
