Experts warn that climate change and economic development - particularly building along rivers and flood plains - will leave more and more people vulnerable to flooding in the years to come.

Preparation has improved and death tolls are falling, but there are still many lessons to be learned.

2007 saw some of the worst floods in living memory, with communities from Britain to China, India and Uganda left struggling to clear up the damage. The poorer the affected populations, the harder-hit they tend to be.

Certain weather configurations - particularly strong waves in the jetstream, high in the atmosphere - can lead to heavy downpours around the world.

Climate experts say global warming could make the problem worse, but warn against attributing individual floods or disasters to climate change.

"You can't attribute particular events to climate change," explains Professor Colin Thorne, head of physical geography at England's Nottingham University. "But on the other hand, the conditions that promote serious flooding will become much more frequent than they are now, so the probability is we will have more extreme events."

Flash floods are usually the most lethal. Heavy downpours, often in mountainous highlands, can lead to surges of water that turn dry river beds or flood plains into raging torrents in minutes.

Local communities usually have little time to flee to higher land, and homes in the water's path can be totallly destroyed. Roads and railways are often made impassable, making delivery of aid much more difficult.

In some ways, the impact of flash flooding can mirror that of the 2004 Indian Ocean tsunami. Giant waves briefly inundated coastal communities after a huge earthquake off Sumatra, but the water swiftly retreated, leaving widespread damage behind.

Other slow onset floods like those that hit Bangladesh every year can also be lethal but tend to give people much more time to move to higher ground. When deaths occur, they are much more likely to be due to disease, malnutrition or snakebites. In 2007, floods in China displaced tens of thousands of snakes into neighbouring areas, increasing the risk of attacks.

Slower floods are also less likely to sweep away property, although it may still be damaged or destroyed. Areas are likely to remain under water for much longer. In India in 2007, some were unable to return to their homes for months.

Storms, cyclones and other maritime extreme weather can also produce storm surges, which overcome defences and swamp coastal areas, as happened in New Orleans in 2005 after Hurricane Katrina.

Huge strides have been made in dealing with the consequences of flooding. A couple of decades ago, floods in Bangladesh used to kill thousands, almost all from disease. Now, cholera outbreaks after floods have been almost eradicated, mainly through better access to sanitation and public education.

Disease worries are always paramount in the aftermath of floods, due to frequent contamination of water supplies and sewage in the streets.

After floods in Sudan in 2007, the Red Cross said local people were drinking water the colour of "milky coffee". Survivors often live in overcrowded camps, schools and other public buildings. Health centres may be swamped with hungry and unwashed children suffering from respiratory, skin and eye infections.

But aid agencies and governments are now much more aware of the risks, and have become better at providing medical services and clean water, as well as giving out information.

Aid workers say they need to raise the spectre of mass disease outbreaks - even if they rarely occur - to prevent people becoming complacent, drinking dirty water and sparking an epidemic.

Even when cholera is detected - something governments are often unwilling to admit because of the stigma attached - medical treatment has improved and fewer people die. For more information, visit the U.N. World Health Organisation web page on cholera.

Early warning systems have also improved, with some countries using text messages to warn communities of predicted flooding.

When floods hit Mozambique in 2000-2001, few were prepared and some 700 people died. Many others had to be plucked from treetops by helicopter. In 2007, aid workers say the government was swift to broadcast radio warnings and evacuate people from vulnerable areas - only 45 people died.

Responding immediately to flood disasters almost invariably comes down to local and national governments. The United Nations and other external agencies usually lack immediate capacity on the ground.

In China, authorities generally use the army to move sometimes millions of people from affected areas. There is invariably demand for helicopters both for rescue and food distribution - and often complaints there aren't enough.

Large developing countries like India are usually reluctant to call for international aid, even when aid workers believe it's needed. Experts say it can simply be a matter of pride, but also point out that governments may have more resources available than outside actors in the early days of a disaster.

The 2005 Hurricane Katrina disaster in New Orleans showed that even wealthy countries such as the United States might struggle when faced with widespread flooding.

"With floods, the first thing to learn is that you cannot stop them," says Professor Graham Chapman at Lancaster University. "You have to have a society that learns to live with them."

Rural communities from the Zambezi in southern Africa to Bangladesh have traditionally used small mounds of raised ground to escape floodwater. But rapid urbanisation and reliance on dykes and embankments built by European colonisers have reduced the emphasis on traditional coping strategies.

Raised railway lines and roads can limit drainage and stop water escaping - which is why they are so often swept away, experts say. And yet post-disaster Western aid frequently concentrates on rebuilding them exactly as they were before.

In many flood-prone regions, drainage is inadequate, while building is carried out without regard to flood patterns. Often, there are no plans to prevent or cope with flooding at all.

Experts recommend building houses that are more durable and survivable, and can be brought back into use within a couple of months of a flood disaster rather than over a year.

In Bangladesh, some pumps bringing up water from the underground water table have been deliberately raised above the level of likely floodwater, keeping them in service even in the event of flooding.

In parts of rural India, aid agencies have educated families to keep food in a place that won't easily be flooded so they can take it to higher ground in the event of disaster. Small boats can be pre-positioned to help with evacuation and rescue, and local staff trained to carry out these operations. Teaching people to swim can also save lives.