On a sweltering summer afternoon last year, Jacqueline Arellano and James Cordero were out in a desert area on the border between California and Mexico, when they ran into a man in his 60s, who was alone, disoriented and wearing a wool sweater and loafers.

"He'd been lost for three days," says Cordero, "and he'd been going to the top of every nearby mountain, to try to get a better view of where to go, because he couldn't tell which direction was what."

Arellano asked him where he was from. Venezuela, he told her, but, "yo no tengo pais. I don't have a country. I don't have anywhere else to go."

She and Cordero gave him water, and offered medical aid.

This encounter is representative of what Arellano and Cordero do. They run a non profit organization called Border Kindness. They go to the desert, where they drop off water, food and first aid along migrant routes into the US. For the last eight years, they've worked mostly on the Mexico-California border.

But recently, they've received a lot more missing persons reports from further east, near the Arizona border. The desperate calls from friends and families of those who have disappeared signal it's time to draw new maps of new routes being carved out by migrants. The maps, for their own use, help them mark where they can start giving aid — like water, food and dry socks.

Like many of the volunteers in their group, Cordero and Arellano were inspired in part by hearing the stories of their own family members who crossed — why they did it, and how terrifying it was. They also are motivated by the humanitarian crisis at the border that has grown more dire in the last few years.

They both feel they have the moral obligation to help save lives out here. Cordero says having a child especially made him committed to the work. When he hears stories of parents attempting to reunite with their children in the U.S., or bringing their kids to escape danger,"I think, that's something we would all do."

The recent rise in unauthorized border crossings isn't limited to any one area. The number of migrants apprehended and expelled across the entire southern U.S. border has skyrocketed: more than 200,000 in November last year alone. Numbers that high were seen during the last major wave of immigration, over 20 years ago.

One major factor for the increase has been the pandemic and it's aftermath, says Professor Raquel Aldana, with the UC Davis School of Law.

"Even in the U.S., we are experiencing inflation and some economic challenges that feel a little more permanent, or at least lingering," Aldana says. "But the effects of the pandemic in economies of the global south have been pronounced and severe."

Many migrants first attempt to travel to a neighboring country, but several Latin American nations have closed off their borders. In 2018, Ecuador cut off entry to Venezuelan immigrants. At the start of the pandemic, Brazil followed suit. Haitians, have been expelled or discriminated against throughout Latin America and the Caribbean. This has created a domino effect where migrants find their way to the border, hoping to find asylum in the U.S.

Those who grow desperate decide to cross into the U.S. on their own. One of the major challenges Border Kindness faces is how to draw a humanitarian aid map for people who do not want to be found.

The answer: follow the items left behind.

Some parts of the desert look more like a shipwreck. Hairbrushes, tooth brushes, shoes — lots of shoes — life rafts and life vests for crossing the nearby All American Canal are scattered across the ground.

Arellano and Cordero have become fluent in the language of discarded items. If the bottles and cans are made in Mexico, they belonged to migrants; the level of condensation in the bottles indicates how recently people have come through here.

The items also tell the story of how much immigration is changing. Those crossing used to be predominantly Mexican and Central American. But now, Arellano says, "we've been finding currency from Brazil, from Colombia, from Panama. From all over the place. And that's different."

Where they find signs of people passing through, they drop a pin in Google maps with a note: this area needs supplies.

The discarded items also speak to how dangerous it is to cross this area. Along the way, they find multiple sets of coroner's gloves littering the sand. Last year set a grisly record for migrants trying to cross the US-Mexico border without documents. More than 800 people died across the entire Southwest border. Many were drownings in the canals and rivers that separate the U.S. from Mexico. But it also was due to heat and dehydration in desert areas like the one Arellano and Cordero were standing in on this day.

If the deaths are discovered, local and federal authorities are notified. Border Patrol agents who regularly monitor the area acknowledge the challenges.

In a statement, the Border Patrol told NPR, "most who choose to enter the U.S. unlawfully are unprepared for the life-threatening dangers they will face." The statement also said, in part, that the "Border Patrol has invested in programs, resources, and infrastructure to allow agents to accomplish their border security mission and preserve human life."

On this day, Arellano points at a Border Patrol truck, about a block away, watching them. She keeps moving and they keep their distance. Over the years the group's relationship with Border Patrol has ebbed and flowed. In the past it was tense; they've also been thanked by agents for helping prevent deaths on the border.

"There was mostly negative interaction with Border Patrol agents during the first few years in the desert," says Cordero. "But in the last few years, we haven't really had many bad interactions. We have used Border Patrol as a tool for search and rescue, for a while reaching out and communicating with Border Patrol to see if they have a search in progress for a certain person or if they have records of them in custody."

Crossing these areas has always been extremely dangerous. In the past, Arellano says, people were more prepared. Recently, volunteers have seen a shift in crossing without the traditional guides — Coyotes — who are hired to smuggle people into the U.S. without documentation.

"Especially in the last two years, we have been encountering people either alone or in pairs that are in pretty bad shape," Arellano says. "They've told us that they were under the impression that it wasn't going to be as difficult as it was. They never could have imagined."

The complexities of immigration, combined with politics, has kept any long-term solutions in limbo.

The Biden administration has enacted a number of policies designed to discourage people from going to the border. They've elicited criticism from both immigration advocates and from Republicans. The bottleneck continues.

Title 42 — a pandemic-era policy that allowed border authorities to detain and expel migrants without the traditional legal proceeding — is set to end in a few weeks. Some Texas cities along the border have declared states of emergency, anticipating more crossings. The emergency declaration makes it easier to file for federal aid.

"The solution isn't at the border" says Professor David Hernandez, of Mount Holyoke College "You can process people and all that. But I think you need to stabilize nations abroad. We just focus on the short term, the wall, the tinkering with asylum policy, and it doesn't really work. There's instability abroad and people are fleeing their countries. And that's not going to stop with a wall. "

For Arellano, Cordero and other volunteers, they're running against a clock. Summer brings heat. As Cordero points out, increasingly extreme weather means they are in a constant race against the desert heat.

"Climate change is real," says Cordero. "Summer of 2020 we experienced temperatures up to 130 degrees. This summer, we just have to plan and prepare that it's going to be the hottest summer on record. It's kind of a recipe for disaster. It's a killer out here."

In some parts of this new route they are exploring, Arellano and Cordero are already leaving bottles of fresh water in bushy areas, where people may be taking refuge from the sun.

They check to see if anyone drank from them.

Arellano picks up the bottle. "Slashed", she sighs.

This is where Border Kindness runs into one of the biggest hurdles in drawing a new map: not climate, not geography, but people. Occasionally, when they leave these bottles of water, they return to find them destroyed.

They don't know who is doing it - but there's plenty of people out here who disapprove of the work they do.

"If they recognize what the water is for... they'll slash it. In hopes people die I guess?" Arellano says.

As they move along, Arellano and Cordero find about a dozen destroyed water bottles at various locations. All mangled. They replace them.

Before calling it a day, they drive up to one last spot where a migrant was found dead from dehydration just a few months ago.

In the nearby bushes, there's the usual: shoes, socks, also, a small child's pink winter glove, and a tiny winter jacket. It's baby blue and filled with caked mud. Arellano inspects it's tags. "4-T", she reads out loud. It belonged to a 4-year-old child.

They walk over to check on the water bottle they left here a few days ago, to see if anyone was able to drink.

But it, too, has been slashed open.