Seven weather disasters, including tornadoes, droughts and a flood, cost the United States at least a billion dollars each last year and killed more than 100 people, US authorities said Wednesday.

While the total cost will not be added up until later this year, experts said 2013 was rather quiet compared to the previous two years in terms of the number of big disasters.

"We saw a relatively benign year, especially when compared to the really increased extremes that we saw in 2011 and 2012," said Deke Arndt, chief of the climate monitoring branch at the National Oceanic and Atmospheric Administration's (NOAA) National Climatic Data Center.

There were 14 billion-dollar weather disasters in 2011, and 11 in 2012, NOAA said.

Despite the decline last year, Arndt said he and colleagues are "very confident" that the planet is indeed warming, and that more extremes of heat and rain are ahead.

"We expect to see more big heat or stronger more frequent and perhaps longer lasting heat waves as the world gets warmer, and we do indeed see that over the long term," he told reporters.

"We expect to see more big rain, in the form of both the biggest rains getting bigger and a typical place in the US depending more on large events to make up more of their annual water budget," he added.

"And we would expect to see fewer big cold events, and we also see that in the data."

The costliest weather disasters last year comprised five severe weather and tornado events, a major flood event, and the western drought and heat wave, said the report.

"Overall, these events killed 109 people and had significant economic effects on the areas impacted," it said.

However, the number of North Atlantic hurricanes during the season -- just two, Humberto and Ingrid -- was the lowest in 30 years, said the report.

"The number of hurricanes and major hurricanes was well below average. The last time only two hurricanes were observed in the North Atlantic was in 1982," NOAA said.

The tornado count for the year was below average, too, according to the annual summary.

The total of around 900 documented tornadoes for the year, marked the lowest annual count since 1989. The yearly average for tornadoes is around 1,250, the report said.

The most expensive damage of the year from tornadoes occurred in May, both in the midwest and in the northeast, followed by an Ohio-Valley tornado outbreak in November.

Other costly weather disasters included floods in Colorado and a drought accompanied by a heatwave in the western states that lasted from March to September.

Severe weather in the southeast in March and in the midwest in April were also both billion-dollar events, NOAA said.

Last year was slightly below average on a government index of the highest and lowest weather extremes, including temperature, precipitation and cyclones, the agency said.