Sign at the Grand Canyon warning of the dangers of hiking unprepared in the hot desert | Photo: xoque/Flickr/Creative Commons License

Dave Legeno, an actor who achieved fame playing the werewolf Fenrir Greyback in a trio of Harry Potter movies, was found dead [Sunday] by a group of hikers in Death Valley, likely of heat-related injuries. And his death serves as a reminder of the extreme danger the desert poses in summer to those visitors who don't take high temperatures sufficiently seriously.

Legeno, 50, was an accomplished martial artist and by all accounts in excellent condition. Authorities are saying he appears to have died of exposure to extreme temperatures in the washes near Zabriskie Point.

And though the precise circumstances of his death may never be known, it's very likely he'd be alive today had he followed a summer hiking survival tip widely known among those of us who live out here in the desert: Don't go hiking.

That seems on the face of it an absurd prohibition, so let's break it down.

Don't go hiking in midday in the desert when it's hot.

If you hike at cooler times of day, don't do it by yourself. Remember: it was a group of hikers that came upon Legeno and made it out to report the tragedy. Having a friend or five along means if you sprain an ankle or have some similar problem, you're likelier to get back out to safety before it gets really hot.

And don't walk out into the desert in summer at any time without bringing way more water than you think you'll need, starting at a gallon per person per day.

Though the British press has described the location where Legeno died as "remote," he was actually found in one of the most accessible and populated areas of the park. He was a mile in either direction from busy roads, and about three miles from a swimming pool, medical aid, and a four-star restaurant. That things went so badly wrong for the supremely fit Legeno with help so close at hand ought to convince anyone paying attention that midday hiking in the summer in the desert during a heat wave is a bad idea indeed.

Those of us who live here tend to know better. There's nothing to convince you of the implacability of the summer desert sun like getting through a normal day in the desert, running errands and doing chores and getting from home to work and back.

If it's taxing to engage in the normal sedentary American lifestyle during a Mojave summer, it's even more so to ramp up your activity to things like hiking in unfamiliar desert canyons. That's why people who actually know the desert well, who live here in the summer and know viscerally how quickly heat exposure can cause problems, simply avoid hiking at low elevations in midday on hot days.

Death Valley National Park's safety advisory puts it even more broadly: "Do not hike in the low elevations when temperatures are hot." The spot where Legeno was found was between 200 and 600 feet in elevation above sea level, which definitely qualifies.

That broad advisory makes sense in places like the floor of Death Valley, where nighttime summer temperatures might not cool down much past the triple-digit mark. Average low temperatures for Furnace Creek in July stand at 88 degrees, which means that on half the nights in a typical July the air temperature at 2:00 a.m. will be higher than that.

Elsewhere in the desert, where nighttime summer temperatures might drop down to a relatively refreshing 79° or so, desert rats who crave some time on the trails will get up and out of the house by 5:00 a.m. or so. The hiking day generally ends at 10:00 a.m., with a few hours' siesta and then perhaps another couple hours after the sun goes down.

There are exceptions, of course: it is possible to take a short walk during midday and live to tell the tale. In 2005, when I was likely in the best shape I've ever been in, a friend and I walked out onto the salt flats at Badwater, at 282 feet below sea level, at 3:00 p.m. on a very hot day. The temperature up the road at Furnace Creek was 117° in the shade: at Badwater in the sun, with salt crystals reflecting most of the sunlight back at us, it was likely a few degrees hotter. We walked about half a mile out and back and that was more than enough.

But there's something visitors to the desert don't understand about those short summer midday walks: even they can go badly wrong. What might seem a trivial jaunt in Oregon or the south of England can be a life-threatening ordeal in the California desert.

We regulate our body temperature in extreme heat by sweating, and that uses up a lot of water. Which means we need to replace it. When temperatures get as hot as that, a typical person will need to drink at least a gallon of water a day if they spend the day sitting in a chaise in the shade with a fan aimed at them. Add even a little bit of physical activity and that gallon won't be enough. Few hikers not accustomed to the desert think to being even so much as two liters of water when they set out on a five- or six-mile hike.

It's not just the California desert, of course. A young man visiting Phoenix from Seattle perished in May on a trail that was at no point more than half a mile from suburban developments. He apparently had less than a quart of water with him when he reached the trailhead. Sit at the first water fountain a mile and a half down the Bright Angel Trail in the Grand Canyon in April and May, and you'll likely see a Park Ranger stationed there to dissuade ill-prepared visiting hikers from attempting to make it down to the Colorado and back, generally carrying a pint or so of water.

People not from here just do not get how dangerous that is. They think they can tough it out. But in the desert in summer, people who tough it out die. Every single summer adds to the death toll, and a high percentage of the dead are people who came out for a bit of exercise.

In past years, we've run articles on what kinds of illnesses can befall unwary desert visitors in the first minutes and hours of overexposure to heat, as well as how to administer first aid to people who show those frightening symptoms.

But why risk it? The midday sun bleaches out the colors and fine detail in the desert, and any animal in the vicinity will be either underground or hidden away. Far better to hike when the sun's low in the sky anyway. You'll see more, and you might just live to tell about it.