NU Online News Service, June 22, 3:29 p.m.EST

Aon Benfield says U.S. insured losses in April and May arenearly triple the annual average over the last 20 years.

Losses from thunderstorms in the two-month span reached about$15 billion. Economic losses stand at an estimated $21.65 billion,says Aon Benfield, the global reinsurance intermediary of AonCorp.

A new report from the firm breaks down severe weather events inApril and May into eight timeframes, five of which werebillion-dollar catastrophes.

The costliest was a set of storms April 22-28 that cost insurersan estimated $5 billion in losses. This period included 334tornadoes, the largest outbreak in history. An EF4 tornado hitTuscaloosa, Ala. and at least three EF5 twisters touched downelsewhere in the Southeast and Tennessee Valley during this timespan, according to Aon Benfield.

Storms from May 21-27 caused an estimated $4.5 billion ininsured losses. This system included an EF5 tornado that toucheddown in Joplin. Mo.

Adding weather events as of mid-June, insured losses total atleast $15.5 billion. Average annual insured losses from severeweather from 1990-2010 are about $5.5 billion, adds AonBenfield.

Catastrophe risk modelers estimate insured losses of between$2 billion and $6 billion for the late April tornado outbreak.AIR Worldwide adds up to $7 billion in losses due to late Maystorms.

The tornado outbreaks led to a historic number of deaths—585 inthe eight events highlighted in Aon Benfield’s report and more than150 in Joplin alone. The reinsurance intermediary comments on theloss of life, surmising that several factors are involved:population growth, tornado strength, time of day, building type,and building strength.