Severe US storms will lead to multibillion-dollar insured losses, according to Aon Benfield subsidiary Impact Forecasting.

The most severe outbreak of storms late last month and early this month featured tornadoes, straight-line winds, large hail and heavy rainfall.

They killed 20 people in parts of the plains, midwest, southeast, mid-Atlantic and northeast regions, with total economic losses expected to exceed $US1 billion ($1.36 billion).

Cyclone Debbie, which swept across parts of the South Pacific islands, Australia and New Zealand from late March into the first weeks of last month, killed at least 14 people.

Impact Forecasting says insured losses are estimated at $US970 million ($1.32 billion) in Australia, and tens of millions in New Zealand.

Debbie’s overall economic cost was estimated at about $US2 billion ($2.71 billion).

“Much of the focus [last month] was once again on the US, as powerful thunderstorms and excessive rainfall led to considerable impacts to central and eastern sections of the country,” Impact Forecasting Meteorologist Steve Bowen said.

“The industry in the US is well on its way to facing its 10th consecutive year of annual payouts of $US10 billion ($13.58 billion) or more for the severe convective storm peril.”

Elsewhere, a “coastal El Nino” led to heavy rainfall in parts of Colombia, killing an estimated 400 people after debris flows destroyed dozens of neighbourhoods.

Major flooding in northeast Bangladesh led to agricultural damage exceeding $US350 million ($475.12 million), and similar events in Iran killed 48 people and caused damage beyond $US353 million ($479.2 million).