WestVic Dairy News - February 2011 Edition
Our exciting 2010 weather: was it extraordinary?
Andrew Watkins and Catherine Gantor Bureau of Meteorology and Rod Eldridge DPI Colac
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To state the obvious, 2010 was wet, very wet! I hear people saying that this is what it used to be like and, coming off the back of 13 years of average to below average rainfall, it is a return to “normal” conditions.
Looking over the long term annual rainfall records for Victoria, 2010 was the fifth wettest year since 1900, and also the wettest year since 1974, with only one year of similar rainfall (1992) in those 35 years. For 2010 most of western and central Victoria received decile 10 rainfall, meaning it was amongst the wettest 10 percent of years on record, with some locations receiving their highest annual rainfall on record (see Figure 1).
Figure 1 Victorian 2010 Rainfall Deciles
Why was 2010 so wet?
A strong La Niña event occurred in 2010 (the opposite of the dreaded El Nino). A La Niña event is characterised by a “tongue” of cooler than normal sea surface temperatures (SSTs) across the central equatorial Pacific Ocean and often has warmer than normal SSTs to the north of Australia (see Figure 2). In addition to the La Niña event, the Indian Ocean Dipole (IOD) was in a negative phase during late winter and spring, associated in part with warmer SSTs in the Indian Ocean off north-western Australia.
Figure 2 Sea Surface Temperature Anomaly (degrees C)
While the science is not settled as to the degree with which La Niña and the IOD are separate, it is known that both the La Niña and the IOD negative phenomena can be associated with above average rainfall across south-eastern Australia. When a La Niña event and a negative IOD event coincide, as in 2010, the result can be a very wet year. Until 2010, this had not occurred since 1975, another wet year in Victoria.
During the second half of the year, the Australian region experienced very warm SSTs, particularly across the northern region. In fact, for the individual months of June and September to December, the Australian region had its warmest monthly SSTs on record.
Globally, 2010 was also one of the warmest years on record. Warm air has the potential to hold more moisture than cooler air. Aided by the increased evaporation from warmer SSTs and higher humidity, this can lead to a greater number of heavier rain events as tropical moisture moves southwards over Victoria.
What about future trends?
While 2010 has been a welcome change to the recent run of dry years, unfortunately it does not necessarily herald a return to the good years of the 1950’s. The science, and indeed the past decade, suggests our long term climate is slowly becoming more arid (see map below). While there will still be variability on top of this trend, and hence we will still have some wet years, it is likely that these will be the exception rather than the rule.
It is also likely that when the wet years come they will contain more extreme rainfall events, and this is where there can be too much of a good thing. Just ask anyone that was trying to get hay done or crops off during December and think back to how wet August was and the troubles that it brought.
Or look at the havoc wrought by recent flooding. The challenge for farmers will be to manage the climate variability against a background of a drying trend, and make the most of the opportunities it presents.
Managing the future.
Farmers have long managed to cope with climate variability. The challenge for the future will be adapting to a changing climate and managing the potentially greater variability of extremes.
Together these will impact upon many aspects of the farm, such as pasture growth, herd health and heat stress, fodder availability, the quality, cost and the availability of water.
However, the experience of coping with the challenges of the past will equip farmers well for challenges in the future. For more information, contact Rod Eldridge on 52335593.
