Those numbers will be driven up in the coming decades as climate change amplifies the destructive power of cyclones, flooding and drought, said the report, released on the margins of high-level UN climate talks in Marrakesh.
Up to now, global calculations of the damage wrought by Nature on communities have not adequately taken into account disparities in wealth, according to the 190-page report, entitled "Unbreakable: Building the resilience of the poor in the face of natural disasters".
"One dollar in losses does not mean the same thing to a rich person as a poor person," said lead author Stephane Hallegatte.
"The same loss affects poor and marginalised people far more because their livelihoods depend on few assets, and their consumption is closer to subsistence level."
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Today, a government deciding where to install infrastructure to avoid urban flooding would logically favour a wealthy district that suffered USD 20 million of property damage over a poor one where asset losses totalled USD 10 million.
Building dikes and drainage systems in the poorer area "would generate lower gains in avoided assets loss, but larger gains in well-being," the report said.
The true cost of natural disasters have been vastly underestimated, it concluded.
A recent UN study of 117 countries, both rich and developing, estimated total global asset losses from natural disasters at USD 327 billion (304 billion euros) a year.
But if lost consumption -- when medicine or schooling for example that was barely within reach before becomes unaffordable -- is included, the bill totals about USD 520 billion annually, the World Bank found.
"This is surely a conservative figure," Hallegatte told AFP.
Myanmar's Cyclone Nargis in 2008, which claimed some 140,000 lives, caused some four billion dollars in damage, according to the UN.
But it also forced up to half of the country's poor farmers to sell off land and other assets to relieve debt following the cyclone, pushing them deeper and more irretrievably into hardship -- making the true cost much higher.