Northern California's deadly wildfires have aggravated the most expensive firefighting season on record, increasing the urgency for Congress to address funding and management challenges at the U.S. Forest Service, the largest government agency that responds to wildfires.

As of Tuesday, state officials said 17 fires across 115,000 acres of California's wine country had killed at least 15 people and damaged more than 1,500 structures, including homes and businesses. About 20,000 people were forced to evacuate. The collective damage prompted President Trump to approve a disaster declaration for California Tuesday, unlocking federal aid to supplement state and local recovery efforts.

While the vast majority of the fire occurred on private land, lawmakers and experts said federal resources have been deployed to help local officials, further challenging the overstretched Forest Service.

"I will guarantee there are a lot of Forest Service and federal resources on the fires," said Robert Bonnie, who was the Department of Agriculture's undersecretary of agriculture for natural resources and environment in the Obama administration. "It doesn't matter where the fire is, they will call in the closest resources."

Bonnie said California would be expected to repay the Forest Service. But he said the fires in California compound funding woes at the Forest Service, which in recent years has had to borrow from other accounts because its firefighting funding runs out every year.

"All those non-direct firefighting programs do get depressed because of the firefighting expense," Bonnie said. "So the Forest Service doesn't have as much resources for preventative measures, such as working with local communities to have them better prepared for fires."

This year has been the most expensive fire season on record for the Forest Service, with fire-suppression costs exceeding $2 billion.

Recognizing the threat, the Trump administration last week sent Congress a disaster relief request for Puerto Rico that includes money for wildfires. The Trump administration is seeking $576.5 million for wildfire suppression funding. House Minority Leader Nancy Pelosi, D-Calif., on Tuesday called on Congress to approve more funding for California's wildfires, but she did not specify an amount.

But lawmakers seeking funding and management reforms at the Forest Service say the emergency funding will only help the agency recoup firefighting money it already spent by borrowing from other accounts.

"That emergency funding is really looking backwards, and I am still concerned about what happens in the future," said Rep. Bruce Westerman, R-Ark., in an interview with the Washington Examiner. "It does nothing to fix the fire borrowing problem or promote more management of federal lands."

As costs have risen, Congress has tried for years to fix the funding mechanism for fighting forest fires but has failed to find consensus. The problem is that under current law, forest fires are not treated the same as other natural disasters such as hurricanes. That forces the Forest Service to take money from accounts dedicated to preventative maintenance, such as clearing underbrush.

Multiple bills have been introduced in Congress to address the funding problem, but lawmakers differ on the best path forward.

Some Republicans, led by Westerman, are pushing for any funding to be matched by forest management reforms that they say would address the root causes of fires and prevent them from being started in the first place.

Westerman introduced legislation that addresses the funding issue, allowing extreme wildfires to qualify for money from the Federal Emergency Management Agency.

The bill also contains other, more contentious reforms allowing the Forest Service to thin trees in forests that are 10,000 acres or less using a shorter environmental review process under the National Environmental Policy Act.

The Forest Service then could more quickly pursue what are known as "forest management projects," in which the agency removes dead or dying timber and sells it to mills, and then can use the proceeds to care for the forests and make them more resilient to wildfires. Other projects could include doing prescribed burns, planned fires done for research purposes.

Environmentalists and some Democrats oppose those reforms, arguing they weaken environmental reviews too much and encourage litigation against the Forest Service.

They say Congress should address the funding problem first, especially as fires have become larger, more frequent and more expensive, which many climate scientists say can be attributed partly to increasing dry conditions caused by climate change.

Fires now are also considered more dangerous because they are burning closer to homes and people as the West becomes more populated.

"We're still trying to work with Republican colleagues to find a lasting solution to this problem, but we're hampered by them refusing to admit that climate change is real and contributes to the problem," said Rep. Raul Grijalva, D-Ariz., in an email to the Washington Examiner.

Grijalva, the top Democrat on the House Natural Resources Committee, supports an approach offered by Sen. Ron Wyden, D-Ore.

Wyden introduced legislation last month that would allow the Forest Service to use disaster relief funding once the original money dedicated to fighting fires runs out. It does not contain management reforms favored by Westerman.

"Longer wildfire seasons are becoming the norm, with more dangerous and more expensive fires making it more crucial than ever to fix the broken way the federal government funds and prepares for these disasters," Wyden told the Washington Examiner in an email. "This is urgent business for Oregon, California, Idaho and other states across the West. That's why [we] are continuing to push our legislation to end fire borrowing and give the Forest Service the funding it needs to start getting ahead of these devastating infernos."

Westerman said a funding-only approach won't do anything to stop future fires.

"It's very shortsighted to think you can throw some more money onto the problem this year, and not have to deal with it anymore," Westerman said. "That's what's been happening."

"I say climate change is real and it contributes to the problem," Westerman added, addressing Grijalva's criticism. "But climate change or not, not managing the forest drastically contributes to the problem."

Westerman, the only licensed forester in Congress, told the Washington Examiner that House leadership has assured him it favors his approach.

He said he expects the House to vote on his bill in late October, but he acknowledges resistance in the Senate.

"We need the management piece in place if we want to stop the tide of catastrophic wildfires out West," Westerman said.