THAMO, Nepal -- Dawa Tshering Sherpa remembers the 1985 flood as if it happened just yesterday. At that time, Sherpa, a then-trekking guide living in this riverside village in the Mount Everest region, was home, resting after lunch.
"Suddenly, I heard a sound like a thunder," the 68-year-old recalled over tea on a recent day. "I looked out from the window and saw a dark river coming down from the mountain."
Sherpa ran out of his house with his wife and 9-year-old son, watching the river -- mixed with rocks, mud and livestock -- passing along his village a quarter of a mile away.
"The river crashed everything standing on its way," he said. "It felt like an earthquake. My house was shaking. I thought the whole village would be destroyed."
Luckily, the flood did not get closer and faded away a few hours later. Sherpa returned home with his family after dark, but he found himself unable to fall asleep.
"I looked at the window all night, afraid that another flood would come down," he said. "I thought it was a punishment from God, until two days later, I heard from other villagers that the flood was caused by the burst of a glacier lake in the upstream."
That was the first glacier lake outburst flood that Sherpa and his neighbors have experienced, but it probably won't be the last. Glacial lakes are a normal feature of mountain geography, formed by melting ice, but as temperatures have increased in recent years, a lot more of them have been created, setting up a time bomb for villages downstream.
At the same time, erratic weather patterns, decreasing freshwater supplies and other problems likely associated with global warming have emerged here, making it more costly and challenging for locals to cater to global travelers.
Mount Everest alone attracts more than 36,000 travelers each year. But experts doubt whether the attraction will persist under changing climate conditions.
When weather becomes strange
"One of the biggest challenges that arise with a series of extreme events is the disruption of the image Nepal has built as a tourism destination," said Marjorie van Strien, a tourism specialist at the International Centre for Integrated Mountain Development, an intergovernment institute of eight Hindu Kush Himalayas countries headquartered in Katmandu.
"The country had just recently rebuilt its attractiveness with an image of being a safe and accessible destination. Extreme events could set these developments back," she added.
Last year, more than 100 flights were canceled in a single week of October because of unusually bad weather. Since air transportation is the only way into and out of the Everest region, the cancellations created a logistical and financial nightmare for the tourists who had to reschedule their international flights or pay thousands of dollars to escape by helicopter.
"Once fewer tourists come, lodges, porters and teahouses and trekking guides and almost everyone living from the airport to the Mount Everest suffer," said Gyelzen Nuru Sherpa, who runs a lodge at the major tourist stop Phakding village.
Sherpa himself lost more than 100 booked guests last autumn, and he says such losses have become more common in recent years. "Weather here became very strange," he said. "In the past, there were always sunny days from September to November. But now, we see cloudy days for one week in a row."
The cost of running tourism businesses here also has increased, as poor weather conditions have stopped flights from coming, cutting off the supply line for rice, sugar and many other provisions to this mountainous region.
Although the warmer weather allows crops to grow in areas that were previously too cold, farming has been threatened by increasingly unpredictable rainfall. Last year, potato growers in many Everest villages failed to harvest due to a missed monsoon rain, and people here ended up trekking a few days to buy potatoes from elsewhere.
Another threat from above
Then there is the problem of getting fresh water. The recent years' decline in snowfall has led to an insufficient recharge in the groundwater that is the main source of water for villages high in the mountains. In places like Khumjung, many streams have dried up, and lodges there have to carry in water from far away.
But none of those problems can be as damaging as glacier lake flooding. In 1985, when the dam containing Dig Tsho glacial lake failed, the resulting flood wiped a miles-long trekking route off the map.
At Thamo, one of the affected villages, Dawa Tshering Sherpa pointed to a place on the riverside that looks like a stone pit. "It was a tree-covered hill," he said. "When the flood came, it pulled down trees, caused a landslide and left many rocks there."
The flood did not cause much trouble to his business, Sherpa said. "At that time, only dozens of tourists came here anyway, and there was no tourism infrastructure," he explained.
"But if another glacier lake outburst flood happens," he continued, "it would create a huge damage to the tourism industry. We now have so many lodges, teahouses and bridges in the downstream. The flood could wash away all of them."
Alton Byers, a geographer at Washington, D.C., nonprofit organization the Mountain Institute, says new glacier lakes are increasingly forming and existing lakes are becoming larger and more precarious.
One such lake, Imja Lake, is now the size of 2,500 Olympic swimming pools. To avoid potential flooding that would threaten downstream villages, a $7.2 million project financed by the U.N. Development Programme has been carried out to lower the lake level.
"But if you think you can lower all those lakes, it is not possible," Byers said. "It is just too expensive. There might come a day that people have to get out of the way."
A skeptic hangs on
For now, tourism is booming here. Some Nepalese move here to help out. Dipak Majar, 28, started a restaurant this year with his brother in Monju, an Everest village that scientists say is highly vulnerable to glacier lake flooding.
"Yes, I heard of Imja Lake, and I know it is potentially dangerous," Majar said while sitting in his restaurant 16 feet above the water. "I'm a bit scared," he added. "When there is a very hot day, I can't stop thinking if the glaciers will melt down and the flood will come."
So Majar puts his mobile phone next to the window to get a better signal. "If something happens in the upstream, I can get a call and run away," he explained.
But still, there is no plan to leave. "We have to make money to support our family," Majar said. "If we go back to our hometown in eastern Nepal, we can't even make 100 rupee [$1] in a day."
Finally, there are people here who simply do not believe in climate change. Among them is Dil Chapa Magar. Although the unusually bad weather last year cost Magar 50 percent of his booked guests at his lodge in Namche Bazaar, he still does not believe that glacier lake flooding and other climate-related problems will come in the future.
"Scientists are just trying to scare away tourists," said the 40-year-old lodge owner. "Before earthquakes, tsunamis and other natural disasters happened, they said nothing about it, and what scientists did say often did not happen."
But what if scientists are right and the flood will come down from the mountain?
Magar replied, smiling: "Then there will be no solution, because scientists said the future is uncertain."
Correction: An earlier version of this story did not correctly describe the International Centre for Integrated Mountain Development.