Emergency organisations could be overwhelmed within seven years by the rising number of people in poor countries affected by floods, droughts, heatwaves, wild fires, storms, landslides and other climate hazards.

Analysis by Oxfam International of the 6,500 climate-related disasters recorded since 1980 show that the numbers of people affected by extreme weather events, many of which are linked to climate change, has doubled in just 30 years and is expected to increase a further 54% to more than 375 million people a year on average by 2015. The figure does not include people hit by other disasters such as wars, earthquakes and volcanoes.

Worldwide emergency aid spending will have to be nearly doubled to at least $25bn (£17.2bn) a year to cope, says the report, The Right To Survive.

"Climate change is set to overload the humanitarian system and destroy the lives and livelihoods of people today and into the future. The system can barely cope with the current level of disasters and could be overwhelmed," said Oxfam's chief executive, Barbara Stocking.

Since the 1980s, the average number of people affected by climate-related disasters has risen from 121 million to 243 million a year. Reported major floods have quadrupled, peaking in 2007/8 when 23 African and 11 Asian countries experienced their worst in memory, heavy rains hit much of Central America, hurricanes created havoc in the Caribbean and cyclones devastated large swaths of Burma and Bangladesh.

The projected increase in climate-related disasters is expected to be driven by more small and medium-scale events which attract the least humanitarian assistance.

"While climate change increases people's exposure to disasters, it is their vulnerability to them that determines whether they survive, and if they do, whether their livelihoods are destroyed," says the report.

"In rich countries, an average of 23 people die in any given disaster, [but] in least-developed countries, the average is 1,052. Poor people live in poorly constructed homes, often on land more exposed to hazards such as floods, droughts, or landslides, and in areas without effective health services or infrastructure," it says.

In addition to the rise in extreme climatic events, people's vulnerability to natural disasters is increasing. "Rapid urbanisation in developing countries means that slums are expanding on to precarious land. The global food crisis is estimated to have increased the number of hungry people in the world to just under one billion. Now the global economic crisis is driving up unemployment and poverty, while undermining social safety nets".

Oxfam called for a fundamental review of the humanitarian aid system, saying that in addition to the $25bn a year for disaster relief, much more would be needed to adapt to future climate change. "A commitment to rich countries spending $42bn a year to help them adapt to unavoidable climate change is a vital first step and in the medium-term, developing countries will need at least $50bn a year."

The report adds: "Finance for adaptation is an obligation – it must be separate and additional to aid commitments, in the form of grants not loans, and disbursed through equitable governance mechanisms."

Oxfam condemned rich countries' reluctance to provide money for poor countries. "Adaptation finance is needed immediately so that developing countries can begin investing in projects to reduce vulnerability. So far, rich countries have pledged $18bn in one-off amounts and less than $1bn has been delivered. In the same time, countries have found trillions to bail out their banking sectors," says the report.

According to the UN's office of humanitarian affairs, there have been climate-related disasters in Burundi, Bangladesh, Madagascar, Colombia, Indonesia, Peru and Bolivia in the past eight weeks.