2010 was the wettest year on record globally according to the US National Oceanic and Atmospheric Administration (NOAA) with Australia experiencing it's wettest September on record, and the wettest year for Queensland with annual rainfall double the average.
La Nina is associated with flooding rains in South Asia, Australia, Brazil and central America. Not only Queensland and Brisbane has felt the force of La Nina, one of the strongest on record. Heavy rain and record flooding has also occurred in Victoria. Overseas, La Nina has brought torrential rains, flooding and mudslides to Brazil killing over 600 people, to Sri Lanka killing 38 and displacing over a million people, and in the Philippines killing 42 people.
In a warming climate we should expect a more active hydrological cycle, with more water vapour able to be carried in warm air, intensifying storm activity and precipitation events, and increasing flooding and water flow. Which is just what was found by Jay Famiglietti, UC Irvine Earth system science professor and lead investigator on a study published in the Proceedings of the National Academy of Sciences in October 2010, which attempted to measure the change in freshwater flow.
During the year a moderately strong El Niño transitioned to one of the strongest La Niña's on record. The El Niño Southern Oscillation (ENSO) is a weather pattern that has a global impact on temperatures and precipitation. It arises from changes in tropical sea surface temperatures (SST) and the air pressure of the overlying atmosphere in the Pacific ocean which changes trade wind patterns and monsoons and can devestate whole regions through drought or flooding rains.
The IPCC 4th report in 2007 found that "Global annual land mean precipitation showed a small, but uncertain, upward trend over the 20th century of approximately 1.1 mm per decade. However, the record is characterised by large inter-decadal variability, and global annual land mean precipitation shows a non-significant decrease since 1950."
A study - Detection of human influence on twentieth-century
precipitation trends (PDF) - published in July 2007 in Nature, concluded "that anthropogenic forcing has had a detectable and attributable influence on the latitudinal pattern of large-scale precipitation change over the part of the twentieth century that we were able to analyse. Our best estimate of the response to anthropogenic forcing suggests (Fig. 1b) that anthropogenic forcing has contributed approximately 50–85% (5–95% uncertainty) of the observed 1925–1999 trend in annual total land precipitation between 40u N and 70u N (62 mm per century), 20–40% of the observed drying trend in the northern subtropics and tropics (0u to 30uN; a decrease of 98 mm per century) and most (75–120%) of the moistening trend in the southern tropics and subtropics (0u to 30u S; 82 mm per century)."
On Precipitation records for Australia the NOAA State of the Climate annual report stated:
"La Niña brought record rainfall to most of Australia toward the end of the year. The country had its wettest spring (September–November; Northern Hemisphere fall) on record. Nationally averaged rainfall was 163.0 mm, which was 125 percent above normal for the period. However, it is noted that in contrast to the rest of the country, southwestern Western Australia had its driest spring on record. With continued extreme wetness in December—particularly in the northeastern state of Queensland, which had its wettest December on record and experienced major flooding—the average precipitation for December was 99 percent above normal, ranking as Australia's second wettest on record, behind December 1975. For the year, 2010 was the country's third wettest since records began in 1900 and the wettest sonce 2000. Southwest Western Australia reported its driest year on record."
That is not good news for Perth. The CSIRO has continued to forecast the south-west of Western Australia becoming steadily drier, and this appears to be the case.
* NOAA, Jan 12, 2011 - NOAA: 2010 Tied For Warmest Year on Record
* NOAA - State of the Climate Global Analysis Annual 2010