FACTBOX-Will Australia's top wines survive climate challenges?

Sept 5 (Reuters) - Australia's A$5.5 billion wine sector is sizing up the impact temperature changes brought on by drought and climate change could have on grape quality.

Here are some facts about Australia's three most popular wine varieties and changing temperatures' possible impacts on them:*

* SHIRAZ (422,600 tonnes)

-- One of the first varieties to arrive in Australia in 1832, shiraz, the same grape as France's Rhone Valley syrah, is known for its spicy, "wild" mulberry flavour.

-- Versatile shiraz is said to take on different characteristics when grown in different regions -- being peppery in cool Victoria, spicy and intense in Coonawarra and Margaret River, powerful and minty in Clare Valley, muscular in Barossa and leathery and rich in the Hunter Valley.

-- Shiraz grapes' versatility in producing this range of wine styles from a broad climate range means that this variety is not as sensitive to shifting temperature as other varieties, such as Pinot Noir. CSIRO researchers believe they will be better able to be adapt to a changing climate than some other varietals.

* CHARDONNAY (397,400 tonnes)

-- Australia's most-planted grape in the 1970s, chardonnay production peaked in the 1980s as critics and consumers tired of what some called its "oaky" and unsubtle character.

-- Still the most versatile white wine grape, it flourishes in cool regions such as Tasmania, Adelaide Hills and Mornington Peninsula, as well as warmer inland regions the Murray Darling, Riverland, and Riverina.

-- Early-ripening chardonnay grapes produce the best wine when grown in a cooler climate, but as with shiraz grapes, they can tolerate quite a wide range of temperatures. Production can be maintained in most regions with higher projected temperatures but quality will be impacted.

* CABERNET SAUVIGNON (274,400 tonnes)

-- A classic "Old World" wine, the full-bodied and blackcurrant-inflected cabernet sauvignon has taken root in Australia's medium to cool regions.

-- Rich and well-structured, it is grown in South Australia's Coonawarra, Victoria's Yarra Valley, the Margaret River, where it is often blended with merlot, McLaren Vale in South Australia and Mudgee in New South Wales.

-- Late-ripening Cabernet Sauvignon grapes prefer warmer climates. An increase in temperature means they could see harvest in regions such as Coonawarra, in south Australia come 15 to 23 days earlier in the year 2030, and 21 to 45 days earlier by 2050, (depending on emission levels) University of Melbourne and CSIRO joint research predicts.

* These three varieties of grapes accounted for 55 percent of all production in the year ending June 2006, according to the Australian Bureau of Statistics.

Sources: Commonwealth Scientific and Industrial Research Organisation (CSIRO, www.csiro.au), Australian Wine and Brandy Corporation (www.wineaustralia.com), Australian Bureau of Statistics, Vineyards Estimates, Australia, 2005-06, (www.abs.gov.au/AUSSTATS/abs@.nsf/PrimaryMainFeatures/1329.0.55. 002?OpenDocument) ((Writing by Gill Murdoch, Singapore Editorial Reference Unit, gill.murdoch@reuters.com, Reuters Messaging gill.murdoch.reuters.com@reuters.net; +65 6870 3922))