GEOFF BENNETT: Good evening, and welcome to the "NewsHour."

The nation remains at the mercy of nature tonight, but nature is showing no mercy; 100-degree heat stretches from the far West across the Deep South.

And a weekend deluge in the Northeast has washed out roads and claimed lives.

In Bucks County, Pennsylvania, standing water from intense flash floods over the weekend has all but dried up.

But in the township of Upper Makefield, just north of Philadelphia, a search-and-rescue mission is still ongoing.

TIM BREWER, Upper Makefield, Pennsylvania, Fire Chief: We have search teams that are assisting us from Delaware, Chester, parts of Bucks County, New Jersey.

We also have deployed canine units, underwater assets, air assets.

And the reason we have done that is, weather conditions have permitted that today.

GEOFF BENNETT: Two children, 9-month-old Conrad Sheils and his 2-year-old sister, Mattie, have been missing since Saturday afternoon.

Upper Makefield Township police released these family photos today.

Officials said their family was driving to a barbecue when seemingly, out of nowhere, Bucks County was inundated with seven inches of rain in 45 minutes.

The downpour claimed the lives of at least five people, including the 32-year-old mother of the missing children.

Scott Ellis, a representative for the family, thanked authorities for their search effort.

SCOTT ELLIS (Sheils Family Representative): We are thankful that they were able to save so many affected by these unprecedented by these floods.

Are we are grateful that they were able to recover many who have been lost.

GEOFF BENNETT: The other four victims were 78-year-old Enzo and 74-year-old Linda Depiero of Newtown Township, Pennsylvania, 64-year-old Yuko Love, also of Newton, and 53-year-old Susan Barnhart from Titusville, New Jersey.

The damage reaches beyond state lines.

In New Jersey, roads were fractured and washed over and cars barely intact buried by debris.

GOV.

PHIL MURPHY (D-NJ): I'm shocked beyond words.

GEOFF BENNETT: Today, New Jersey Governor Phil Murphy said flooding in the Northeast is becoming more and more frequent.

GOV.

PHIL MURPHY: We have seen it, but not at this level.

And I think we all fear that that's going to be the new norm.

And we can't be dragged by that.

We got to get ahead of it.

GEOFF BENNETT: From the East to the West, where Arizonans are sweating and splashing through their new normal.

KALEEL WASHINGTON, Phoenix Resident: If you ever, like, stood next to an oven while you're baking something, it's like that, but, like, it's coming from every direction, and you can't escape it, unless you go inside.

It's very, very hot.

GEOFF BENNETT: An historic streak of heat continues to beat down on Phoenix with no end in sight.

Today marked 18 straight days with temperatures of 110-plus degrees.

That officially ties the previous record set in 1974.

El Paso, Texas also shattered records, hitting its 30th triple-digit day in a row.

The El Paso Fire Department said several park-goers were rushed to the hospital yesterday with heat-related symptoms.

And, nationwide, more than 70 million people live in areas where today's forecasts were dangerously high, all the way from the Florida Panhandle to the deserts of California.

But not everyone is looking to escape it.

In California's Death Valley, keeper of Earth's hottest temperature on record, dozens of tourists posed next to an unofficial thermometer, hoping to see the number tick past the all-time high, a sight to see, but, even more so, a foreboding reminder of climate change and its deadly impact as it pushes our environment to the extreme.

California has been dealing with these extremes, including the heat baking the state right now.

We're joined by Wade Crowfoot, the secretary of California's Natural Resources Agency.

Thank you for being with us.

And you have said that global climate change is supercharging heat waves.

What is your state doing to confront the long-term threat posed by climate change, but also the immediate, urgent threat posed by these heat waves?

WADE CROWFOOT, Secretary, California Natural Resources Agency: Well, most of us across America are not a stranger to hot summer temperatures.

However, in California and across the West, we are experiencing he waves that are altogether hotter and longer.

Parts of California that have never experienced this intense, sustained heat are now suffering these waves.

And so, in the near term, we are focused on ensuring people understand when this heat is coming and understanding what precautions they need to take, identifying where cooling centers are they can go to.

And over the long-term, we are helping build community resilience to these heat waves through things like shading streets and schoolyards, expanding cooling centers, helping people get air conditioning in their homes.

GEOFF BENNETT: On the point about resilience, how is the electricity grid keeping pace with the demand?

How resilient is the grid?

And what are you advising Californians to do in the meantime?

WADE CROWFOOT: Well, last year, we experienced a far higher energy demand than we ever had during one of these sustained heat waves, because more people had to use their air condition for a longer period over that week.

So we are bringing on more energy, and specifically clean energy, to ensure that there is enough energy, that, even when everybody across the state is turning that A.C. on and using electricity, we have enough of it to ensure everybody can stay safe.

GEOFF BENNETT: California's wildfire season is ramping up amid these intense conditions.

How is your state addressing the wildfire risk?

WADE CROWFOOT: Well, hotter temperatures deeper into the summer mean greater wildfire risk.

And we have upwards of 10,000 men and women out there protecting us from wildfires.

We have been really focused in recent years on creating fuel breaks around communities that defend communities, doing the work we need to across our forests and landscapes, so that these fires, when they start, stay fairly small.

Our focus right now is ensuring that everybody is prepared for wildfires that may come this summer.

GEOFF BENNETT: California also has the largest variety of plants and animals of any state.

It also has the world's tallest and oldest trees.

How does this prolonged, extreme heat affect biodiversity?

WADE CROWFOOT: Well, a lot of plants and animals historically have been pretty flexible and able to withstand big temperature variations.

But these extreme heat waves are almost unprecedented, though.

They're getting hotter conditions in our rivers, which is impacting our fish, impacting ecosystems even up into our mountains.

So we're focused on finding areas of wildlife connectivity in coming years and places of climate refuge, where animals can actually migrate to as it gets warmer.

GEOFF BENNETT: You have been doing this work for quite a while.

Have you ever seen it this bad?

How does it change the work that you and your colleagues do?

WADE CROWFOOT: You know, I have never seen it this bad.

And, frankly, we are living on a planet that is not looking like the planet we have been living on as a human species for the last several thousand years.

It's not hyperbole to note that we have had the driest conditions, the wettest conditions, the hottest conditions, the worst wildfires.

We are seeing climate change accelerate and bring these extremes along with it.

And there's so much that we need to focus on in California and our country to combat climate change and protect Americans from these impacts.

GEOFF BENNETT: What are some of the things that you say we need to focus on?

WADE CROWFOOT: Well, one is, we need to green our grid.

We need to demonstrate to the world that we can reduce the pollution that's worsening climate change.

Thanks to the president's leadership and our state's leadership, our governor's leadership, we're focused on doing that.

And there's a lot that we can do to build this resilience to these impacts.

So, in the West, that means creating water systems that are more resilient to these hotter, longer droughts.

There is so much that's happening, and our focus is, show the world that we can effectively combat climate change and protect Americans in the process.

GEOFF BENNETT: Wade Crowfoot is the secretary of California's Natural Resources Agency.

Thanks for being with us.

WADE CROWFOOT: Thank you.