When hikers need assistance on days with extreme heat, National Parks rangers are also put at risk

It's no surprise that hikers seeking adventure would be drawn to the vast wildlands of the country's national parks, especially during seasons when scorching conditions are at their highest.

But when visitors venture to the parks on days when temperatures exceed triple digits, not only are they putting themselves at risk, but the first responders tasked with assisting them should a health emergency occur are placed in harm's way as well, experts told ABC News.

Multiple park visitors died last year when visiting places like Death Valley National Park and Big Bend National Park amid record regional temperatures.

Despite increasing temperatures, national parks are seeing record visitation -- with a 16% increase since 2012, Chad Lord, senior director of environmental policy and climate change at the National Parks Conservation Association, told ABC News.

And it appears as if visitors don't wholly understand how much more difficult rescue operations become during hot conditions.

"Rangers are people too, so we get affected by heat, just like anybody else does," Abby Wines, park ranger at Death Valley National Park, the hottest place in the world, told ABC News. "We might be slightly better at dealing with heat than someone that's traveling from a cooler place, because there really is a biological factor of a climatization to heat. But there are limits to that."

Once temperatures reach above 115 degrees at Death Valley National Park, rangers are no longer allowed to do any "hard work" outside, unless there is a true emergency, Wines said.

And even in the event of an emergency, the ranger in charge of any particular shift is tasked with assessing the situation and determining whether it is even worth it for rangers to respond. In some cases, they won't respond, Wines said.

"If it's potentially hours worth of searching on foot without any idea of exactly where in a broad area of the park a person is, and it's above 120 degrees, then probably not," she said.

Once above 115 degrees, rangers are only permitted to spend 10 minutes performing hard labor out in the heat and must spend the rest of the hour indoors, in a cool place, Wines said.

"That's pretty hard to accomplish when you're rescuing someone pretty far from the trail from the trailhead," she said.

For visitors, anything above 105 degrees is like entering a hostile environment, Angela Lankford, a former ranger for Grand Canyon National Park who witnessed many hikers biting off "more than they could chew," told ABC News.

Simple omissions, such as not bringing enough water or salty snacks, could make the difference between a successful or dangerous hike, Lankford said.

During a 116-degree day in the 1990s, Lankford recalled Grand Canyon rangers needing IV fluids as they conducted a rescue for a hiker. In those conditions, alternate rangers will need to come in to tag-team the rescue, which could delay the rescue even further, Lankford said.

Signage has been instrumental in getting the word out to visitors on the dangers that lie ahead should they decide to hike in the heat, Wines said.

At Death Valley National Park, temporary red octagonal signs read "STOP: Extreme Heat Danger."

These signs, especially the ones that appear temporary, seem to capture visitors' attention most effectively, Wines said.

Many parts of the remote landscape do not have cell service. National park rangers advise visitors to stay on the trails and only hike during daylight hours.

If an emergency happens in the middle of the night, assistance could take even longer, as rangers will need to be paged and awoken in the middle of the night, Megan Smith, preventative search and rescue ranger at Grand Canyon National Park, told ABC News.

Aircraft do not fly at night and experience drops in performance during hot temperatures -- leading first responders to ground them -- complicating matters even further.

At Death Valley, local air ambulances will not respond above 120 degrees because the hot air affects the rotors -- they just don't get enough lift in hot air, Wines said.

"There's a lot of conditions and different factors that it's difficult to explain to people why they had to wait so long," Smith said.

In addition, there may be less staffing at national parks both at night and overall -- the experts said.

"If you have a broken leg and you need to be carried out in a wheeled litter, that's a team of eight or more people," Smith said. "And getting that together can be really difficult."

National parks have about 20% less staff than a decade ago, despite the growing number of visitors -- mostly because of lack of funding, Lord said.

The parks will rarely close due to extremely hot temperatures. Closures are typically reserved for when roads and trails become inaccessible, due to events like flooding and wildfires. It is also difficult to monitor and uphold closures with dwindling resources and staffing, Smith said.

Many of the millions who visit America's national parks every year are international tourists and may not be acclimated to the heat, Smith said.

Not only is it hot during the day, but at night there is often little respite as well, increasing the risk of heat-related illness even more.

There is a common misconception that heat will merely be uncomfortable, but it is the No. 1 weather-related killer in the world, according to the Centers for Disease Control and Prevention.

"There's a lesson to be learned for everyone out there that even the people that live in the hottest place on earth, we limit how much activity we do outside and the hardest part of the day," Wines said.

While national parks in desert settings are adept at dealing with the heat, parks in cooler climates -- like in Alaska -- are increasingly learning how to manage during heat waves or wildfire events, Smith said.

"I think that it is becoming more of a concern for other national parks that don't consider themselves, quote, 'heat parks.'" she said. "And they're coming to us for expertise and inputs."

ABC News' Jaclyn Lee and Tenzin Shakya contributed to this report.