When the fierce Santa Ana winds blew in last weekend many residents were stunned by the speed at which wildfires rapidly overwhelmed their neighbourhoods in southern California.

The supercharged flames destroyed 842 homes in Los Angeles and Santa Barbara — the highest urban tally since 1961 — and were further stoked by ultra-low humidity, soaring temperatures and tinder dry vegetation. Compared with a decade ago, fires are often larger and fiercer. As risks increase, state spending on fighting fires has soared 150% to more than $1bn last year.

A report released last week by UC Berkeley researchers David Roland-Holst and Fredrich Kahrl, entitled California Climate Risk and Response, warned that wildfires, extreme weather and rising sea levels associated with climate change threatened some $2.5tr of the state's real estate assets [out of a total of $4tr], plus hundreds of billions of dollars worth of transport, energy, water and other infrastructure. Annual damage could reach $23bn.

"In the case of fire the real problem for California has to do with the changing seasonal water availability," said Roland-Holst. A key factor is the disappearing Sierra Nevada snowpack, a natural refrigerator that supplied melting water throughout the summer. With rising temperatures the snow melts earlier.

"This leads to the main driver of increased forest fire risk, which is the desiccation of forest soils in summertime. Soils will be drier because they're not getting run-off all year round from snowmelt. That increases the intensity of any fire."


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