California gripped by a record-breaking heat wave, wildfires — and up next, a hurricane

This week, the state of California is experiencing wildfires and a record-breaking heat wave. This weekend, an incoming hurricane could set off heavy rains and flash flooding.

"It certainly feels like a lot of everything all at once, that's for sure. And this is true in actually a lot of regions right now, not just limited to California," Daniel Swain told As It Happens host Nil Köksal.

"And a lot of the things that are happening are exactly the kinds of events that climate science has long predicted would increase rapidly in a warming climate," said Swain, who is a climate scientist with the Institute of Environment and Sustainability at the University of California, Los Angeles.

On Tuesday, the state capital of Sacramento, as well as six other places, set all-time maximum temperature records. Sacramento hit a high of 46.7 C, while Santa Rosa registered a high of 46 C.

A fire in the northern part of the state, in and around the town of Weed, left two people dead and destroyed hundreds of homes and other buildings. Two more people died and a third was injured in a wildfire southeast of Los Angeles, which is still only about five per cent contained, according to the state's fire department.

Hurricane Kay is expected to move up the Baja California peninsula in Mexico and come within 300 kilometres of San Diego, Swain told Köksal.

Here is part of their conversation.

The words historic, record-breaking — we hear them, you use them, when we talk about climate stories. It can be hard for people and desensitizing, I think, at a certain point to give them a sense of what we're dealing with. But as a climatologist, what are you seeing and feeling this week that's shocking even to you?

It's been remarkable in multiple dimensions, not just for the peak magnitude of the heat, which in some places broke not only all-time September monthly records, but all-time temperature records from any month in places like Sacramento, and parts of the interior San Francisco Bay area.

But it's also been a very prolonged event. This has been now a full week of extreme heat. And in some places there's at least a few more days of it. That is a very long duration heat wave for a place where summertime heat waves are often broken by a sea breeze after a day or two. This event has not had any such relief; it's just going on and on.

And the other aspect, too, is that the overnight temperatures have been extremely warm. California often sees heat waves where temperatures, at least during the nighttime, drop to more manageable levels, which allows people and buildings to cool down. In fact, that's one of the reasons why air conditioning in some parts of the state is relatively unusual. There used to be the ability just to open windows and turn on fans and bring in that cool air at night.

But during this particular event, a number of places have stayed record-warm at night in the 80s and even 90s Fahrenheit, straight through the overnight hours.

And in terms of wildfires, new evacuation orders went into effect just this morning in parts of California. I get the sense from you, you think that this heat might make even more fires likely in the next few days.

We've certainly seen a big uptick in wildfire activity in the past week or so, coinciding with this extreme heat in California. But the other thing to remember, too, is that the fire season in California can be, in many years, heavily back-weighted. So it doesn't necessarily peak during the hottest months of the middle of summer, but it actually peaks later in the autumn....

So having this extreme heat event, which resulted in this massive vegetation drying event as well, immediately preceding the autumn wind season, is particularly bad timing. So it's not just a question of the fires that are currently burning during the heatwave, it's also a question of how that has set the stage for worse fires later this fall, if and when those winds arrive before the onset of seasonal rain.

And on top of all of that, there's a hurricane off the coast. How is that going to affect things?

Yes, this is very unusual, actually. California is not a place that sees hurricanes almost as a rule. And to be clear, the hurricane is not going to make landfall in California. But it will make a relatively close approach, moving northwestward up the coast of Baja California [state] in Mexico, and eventually reaching a position within a couple of hundred miles of the coastal city of San Diego. So this will be making one of the closest approaches of any hurricane in living memory in California. So this is a very unusual event.

The impacts will mainly be rain related. It may ironically increase fire risk in the initial hours as the winds will increase dramatically before the rain arrives in southern California. But thereafter, the risk would probably transition more to flash flooding in the mountains and deserts.

So the heaviest rainfall is unlikely to occur in the major cities like Los Angeles and San Diego, but would instead occur over the southeastern desert regions, places that in a typical year only receive an inch or two of precipitation. But from this one storm might receive as much as four or five or six inches. So two to three times the average annual rainfall potentially occurring in just a couple of days in the desert.

Written by Andrea Bellemare with files from The Associated Press and Reuters. Interview with Daniel Swain produced by Chris Trowbridge. Q&A edited for length and clarity.