Floods in Arizona last month were some of the worst since 1970 and caused insured losses of about $US100 million ($112.66 million), according to Impact Forecasting.

The flash floods struck when Hurricane Norbert and Tropical Storm Dolly combined with monsoonal moisture to produce rainfall equal to one-in-1000 year events in some areas.

“The cities of Phoenix, Tucson and Mesa were affected, where thousands of vehicles and properties were inundated,” Impact’s monthly catastrophe report says.

Similar flooding occurred in parts of California and Nevada, according to the Aon Benfield subsidiary.

In Pakistan and India floods triggered by monsoon rains killed at least 648 people and damaged or destroyed 375,000 homes last month.

In India’s Jammu and Kashmir state insured losses were estimated at $US150 million ($169.11 million) and economic losses at $US16 billion ($18.04 billion).

Seasonal rains flooded parts of Thailand, China and northeast India, killing 200 people, damaging 300,000 structures and causing economic losses of more than $US2.1 billion ($2.36 billion).

“Floods causing significant economic losses are on the rise in Asia,” Impact Forecasting Asia-Pacific Head Adityam Krovvidi said.

“Though the insured losses are very low for many events, the potential for a big surprise such as the 2011 Thai floods is high. Pearl River Delta and Ho Chi Minh City among others are good examples in the region.

“Impact Forecasting has recognised the potential for major insured losses and has been developing several realistic disaster scenarios for Asian floods in addition to fully probabilistic models. Work is complete or in progress in Thailand, China, Vietnam, Jakarta and Malaysia.”