What's going on in Australia is rain. British people might think that they're rain experts. Truth is that they hardly know what rain is. The kind of cold angel sweat that wets British windscreens isn't proper rain. For weeks now rain has been drumming in my ears, leaping off my corrugated steel roof, frothing through the rocks, spouting off the trees, and running, running, running past my house and down into the gully, into the little creek, into the bigger creek, and on to the Nerang river and out to sea at Southport. We've had more than 350mm in the last four days. My creek is running so high and so fast that I can't get out and my workforce can't get in. I can't even go for a walk under the dripping trees, because I'll come back festooned with leeches. In these conditions you can end up with a leech in your eye, and there's no one here to help get it out.

The rain comes in pulses. When the noise abates, momentarily, I can see Mount Hobwee through veils of wet mist, and then I hear the advancing roar of the next pulse, and everything shuts down again. Behind my house a white cataract is charging down the gully through the rocks. When I'm in bed I can feel the thudding of its raw power through my bones.

So, yeah, as Australians say, the problem is rain. The ground is swollen with months of it. The new downpours have nowhere to go but sideways, across the vast floodplains of this ancient continent. We all learned the poem at school, about how ours is "a sunburnt country . . . of droughts and flooding rains". Groggy TV presenters who have been on extended shifts, talking floods for endless hours, will repeat the mantra, so hard is it wired into the heads of Australian kids. And yet we still don't get it. After 10 years of drought, we are having the inevitable flooding rains. The pattern is repeated regularly and yet Australians are still taken by surprise.

The meteorologists will tell you that the current deluge is a product of La Niña. At fairly regular intervals, atmospheric pressure on the western side of the Pacific falls; the trade winds blow from the cooler east side towards the trough, pushing warm surface water westwards towards the bordering land masses. As the water-laden air is driven over the land it cools and drops its load. In June last year the bureau of meteorology issued a warning that La Niña was about "to dump buckets" on Australia. In 1989-90 La Niña brought flooding to New South Wales and Victoria, in 1998 to New South Wales and Queensland. Dr Andrew Watkins, manager of the bureau's climate prediction services, told the assembled media: "Computer model forecasts show a significant likelihood of a La Niña in 2010." In Brisbane the benchmark was the flood of 1974; most Queenslanders are unaware that the worst flood in Brisbane's history happened in 1893. Six months ago the meteorologists thought it was worthwhile to warn people to "get ready for a wet, late winter and a soaked spring and summer". So what did the people do? Nothing. They said, "She'll be right, mate". She wasn't.

It takes La Niña to bring rain to the inland, in such quantities that it can hardly be managed. Manage it Australians must. The Wivenhoe Dam on the Brisbane river was built to protect the city of Brisbane from another flood like the one of 1974. For years it has been at 10% of capacity, so when it filled this year nobody wanted to let any of the precious water out. It eventually became clear that the dam had filled to 190% of its capacity, and the authorities realised with sinking hearts not only that the floodgates would have to be opened, but that the opening would coincide with a king tide in Moreton Bay. The question nobody has been heard to ask is whether or not the level of water in the dam should have been reduced gradually, beginning weeks ago. The mayor of Brisbane, aware that a disaster was about to occur on his watch, made a hysterical attack on the opponents of dam building, but what the succeeding events prove is that dams are no substitute for a coherent water strategy.

The phenomenon is anything but momentary; the not-so-exceptional rainfall will continue, probably until the end of March. Professor Neville Nicholls, president of the Australian Meteorological and Oceanographic Society, believes that "the Queensland floods are caused by what is one of the strongest (if not the strongest) La Niña events since our records began in the late 19th century". He was asked if the intensification was a consequence of global warming, and declined to comment. Other people have been rather too quick to claim the extreme weather as a direct consequence of global warming. (It will surprise many readers of the Guardian to learn that in Australia there is still a bad-tempered debate about whether global warming is happening or not.)

One of the penalties of living on the east coast, as most Australians do, is that all the rain that falls on the mountains known as the Dividing Range heads your way. Up here, at the top of the watershed, I have only to fear a landslide, which will happen if slopes now bulging with water actually burst. At sea level, it's anybody's guess. Meteorologists and hydrologists try to predict peak levels and peak times, and have to revise their estimates up and down like yo-yos.

The world is aware of what has been happening in Australia because so much of Queensland's capital city, Brisbane, the "most livable city in Australia", is now submerged in dirty brown water. Smaller towns in Australia have been flooded for months; some have been flooded five times since the beginning of December. What the rest of the world must be asking is why Australians don't take steps to minimise the destruction? In the southern US you could take your Chevy to the levee; Australians rarely build them. An eight-metre levee has kept the town of Grafton dry, though the Clarence river is in massive spate, but Yamba, further downstream has no levee and is under water. Goondiwindi has an 11-metre levee to protect it from the Macintyre river, but hydrologists have predicted a peak of 10.85 metres – far too close for comfort. Evacuations have begun.

When I drove south to see my family for Christmas, I had to drive around the floods in the Riverina; on the way back I had to avoid the flooded Richmond river round Kyogle. The Darling Downs area was inundated in December and has been inundated again; Dalby, Chinchilla, Warwick and Condamine had already started the clean-up, and have had to evacuate low-lying areas for the second time. The second flood in Chinchilla was worse than the December flood; residents have now been told to boil their water because the piped water is thought to have been contaminated by E coli. The Burnett river has flooded Bundaberg again and the Mary river Maryborough. Rockhampton has been under water for a month. There is no guarantee that the end is in sight.

In the case of Toowoomba, Grantham and Murphy's creek, there was nothing to be done. The Lockyer valley suffered a flash flood, in which a sudden deluge generated an eight-metre wave of water that ripped through the towns, drowning people in their cars, popping houses off their stumps, and whirling them down stream. The resulting TV footage has been seen by Australians hundreds of times. It is the stuff of nightmares, with cars and buses bouncing end over end down streets full of people clutching at anything they can find to avoid being swept away. The army is now involved in searching for the bodies of the 61 people still missing; there is no more talk of rescue. The total dead to date is 26. In Brisbane a 24-year-old man went to check on his father and got swept into a storm drain.

The rest of the world might well be scratching its head. Though the rise of the Brisbane river had been predicted for many days, owners left their boats on the river, some of them moored to pontoons, which were themselves ripped from their moorings. Literally hundreds of pontoons went careering down the river, crashing into unmanned powerboats that were already cannoning into each other. A long section of the riverside walkway broke away and became a waterborne missile. A floating restaurant was sucked under a bridge. Some idiots went racing around in the brown surge on jetskis, unmindful of the half-submerged debris that could have smashed them and their jetskis to smithereens. People who insisted on staying in their apartments appear not to have understood that the electricity company would turn off the current, that their refrigerators would not be working, that they couldn't get to a supermarket and that the supermarkets that weren't flooded had no food left. They are the only people who don't know, unless they have a battery-powered radio, what's going on. It could be weeks before the water drains from Brisbane streets, so even these die-hards may have to ask for help from the emergency services.

The official view is that Australians in flood areas are being wonderful. They are pulling together, helping each other, staying cheerful, not complaining. When given the opportunity they make inspiring statements, that they'll rebuild their communities, stronger and better than ever. That they are Queenslanders, who don't give up. (And so forth.) What nobody is talking about yet, is whether the flood risk can be reduced.

The colour of the water reveals a terrible truth. What is being washed downstream is topsoil. The water moves so rapidly because so much of the land has been cleared. Any wooded land will be, like mine, high in the catchment. As long ago as 1923, Sydney Skertchly, an Englishman who had been working for the Queensland government as a geologist before he retired to what is now the Gold Coast suburb of Molendinar, pointed out that rain that fell in the upper part of the Nerang river catchment that used to take five days to reach him on the coastal plain at Molendinar, now reached him in five hours. When the settlers first arrived on the coast of northern New South Wales and southern Queensland, the rivers were navigable. As the "scrubs" (the settlers' way of referring to rainforest) were ripped out, the seasonal rains carried the topsoil into the rivers, which silted up and then began to flood.

The tide of brown water that is now polluting the sea off eastern Australia is bound to damage already damaged marine ecosystems. The world needs Australia to restore its mangroves, which is where the nutrients carried in the brown water would have been recycled. As well as sediment, the brown water carries nutrients and pesticides from agricultural run-off, together with whatever nasties have been washed out of flooded coalmines. Salinity of the sea-water could drop to 10 parts per 1,000 or even less and remain like that for weeks. After the Fitzroy river flooded Rockhampton in 1991, all the corals and sea grasses round the Keppel Islands died. The area had not yet recovered when the brown tide returned at the beginning of January, and keeps coming. The fresh water now entering the seas off Australia is expected to drift northwards to where the Great Barrier Reef is already struggling with rising sea temperatures. In ecological terms, worse, perhaps very much worse, is on the way. Australia owes it to the rest of the world to get a handle on its regular floods. Or she won't be right, mate.

The creatures of the rainforest are used to rain. After gorging on the treefrogs that are mating in a rainpool by the house, a night tiger snake has come up to sleep the day away on my verandah. A rufous fly-catcher is hunting for his breakfast under the verandah roof because there are no insects out in the rain. The regent bowerbird is enjoying his morning shower 50 metres up in the top of the quandong, meticulously grooming each gleaming feather.

Australian-born writer Germaine Greer spends three to four months every year in her home country where she runs the Cave Creek Rainforest Rehabilitation Scheme in Queensland.