A firefighter knocks down hotspots to slow the spread of the River Fire, part of the Mendocino Complex, in Lakeport, California, on July 31 2018. Picture: REUTERS
A firefighter knocks down hotspots to slow the spread of the River Fire, part of the Mendocino Complex, in Lakeport, California, on July 31 2018. Picture: REUTERS

Los Angeles — Fire authorities have insisted they have ample water supplies to fight California’s devastating wildfires — contrary to US President Donald Trump’s tweets that unspecified water diversions to the Pacific were making matters worse.

Officials from the California Department of Forestry and Fire Protection (CalFire) and the National Interagency Fire Center in Boise, Idaho, stressed that wild-land blazes are battled primarily by crews hacking away at dry brush with hand tools and bulldozers, not with water.

"Yes, we have plenty of water," CalFire chief Scott McLean said by telephone.

He said the two largest blazes in California this week — the Carr Fire and the Mendocino Complex Fire — were each ringed by at least three major reservoirs.

The Mendocino Complex Fire, made up of two separate conflagrations that merged, became the largest wildfire in Californian history on Monday, when it grew to 283,800 acres (114,800ha).

It surpassed the Thomas Fire, which burned 281,893 acres in Santa Barbara and Ventura counties in 2017, and was still growing, CalFire said.

McLean said Trump’s tweets, after the president approved a federal disaster declaration requested by Governor Jerry Brown for the fires on Sunday, sparked a barrage of media queries to CalFire.

On Sunday Trump tweeted: "California wildfires are being magnified & made so much worse by the bad environmental laws which aren’t allowing massive amount of readily available water to be properly utilized. It is being diverted into the Pacific Ocean. Must also tree clear to stop fire spreading!"

Then on Monday he tweeted: "Governor Jerry Brown must allow the Free Flow of the vast amounts of water coming from the North and foolishly being diverted into the Pacific Ocean. Can be used for fires, farming and everything else. Think of California with plenty of Water — Nice! Fast Federal govt. approvals."

The White House did not respond to requests to clarify Trump’s tweets.

Peter Gleick, one of California’s leading experts on Western water resources as president of the Oakland-based Pacific Institute, said Trump appeared to be seizing on the wildfires to side with farmers on a separate debate over how to allocate California’s finite water resources among farmers, cities, fish and wildlife.

"There’s nothing that California water policy has done that makes these fires worse or more difficult to fight," Gleick said.

Trump’s references to diverting water to the oceans was "completely backwards", he said.

"The water that reaches the ocean is what’s left after we’ve diverted most of the water away for cities and farms, and what little is left is barely enough for California’s aquatic ecosystems and the fisheries," he said.

The White House did not immediately respond when asked about Gleick’s comments.

Trump’s suggestion that environmental laws were somehow compounding wildfire woes drew derision on Twitter.

Critics said his tweets ignored the greater wildfire frequency and severity experienced in California and other Western states from extreme drought and sustained periods of hot, dry weather, in keeping with the forecasts of climate scientists.

Fire officials have said that 95% of all wildfires are caused by humans, from camp fires left unattended to careless smoking, to sparks from vehicles and improperly maintained power lines.