Mountain events can improve safety with ultra-high-resolution weather models
In late May 2021, 172 runners embarked on a 100-kilometer (62 mi) ultramarathon in northwestern China. By midday, as the runners made their way through a rugged, high-altitude section of the course, temperatures dropped, strong winds blew around the slopes of the hills, and rain and hail frosted the runners. By the next day, the death toll from the sudden storm had risen to 21.
A new study is revisiting the deadly event with the aim of testing how hyperlocal modeling can improve forecast accuracy for mountain events. The runners ran into trouble as hourly weather forecasts for the race underestimated the storm. The steep mountainsides had very localized effects on wind, precipitation and temperature on a scale too small for weather forecasts for the event, according to the new study, published today in the Journal of Geophysical Research: Atmospheres .
Hourly forecasts for the 2021 race were based on relatively large-scale atmospheric processes, with models with a three-kilometer resolution — sufficient for most regional forecasts, but too coarse to capture “hyperlocal” weather, such as the storm that hit. the natural, says Haile Xue, a climate scientist at China’s CMA Earth System Modeling and Prediction Center and lead author of the new study. Although a wind and cold temperature advisory had been issued the night before, it lacked the resolution needed to locate the danger zones on the track.
“An apparent temperature forecast based on a high-resolution simulation can be useful” in addition to general regional forecasts, Xue says. Conditions such as the storm of 2021 are common in extremely high-elevation mountains, such as Mount Everest and Denali, the newspaper said. Although less frequent at lower elevations, when such storms occur, they can strike suddenly and lead to injuries and loss of life.
The new study uses topographical data from the orbit, with a resolution of tens of meters instead of kilometers, to model the hyperlocal weather conditions created by the mountains. With a resolution two orders of magnitude finer than the original predictions for that weekend, as well as detailed considerations of mountainous topography, the model accurately reconstructed the race’s storm conditions and offered even greater insight into what might have happened that day.
The original forecast included a large-scale cold front, which would have led to temperature drops and stronger – but not extreme – winds, with only a low-level wind recommendation. The new study found that the apparent temperature could have dropped to -10 degrees Celsius (14 degrees Fahrenheit), about 3 degrees Celsius cooler than what the original models predicted.
The model also generated an ‘impact prediction’, including apparent temperature, which could have been even lower because it takes humidity into account and ideally would include the effect of wet clothing or skin on body temperature. Including these in forecasts, Xue says, can reduce the risk of hypothermia.
In addition to the weather, the schedule for the race and equipment requirements for the runners were discussed after the event. Many endurance events require adequate layers for protection from heat and rain; these were suggested but not required, which could have contributed to the loss of life. Both accurate weather forecasts and equipment requirements are essential for a safe event.
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Haile Xue et al, Simulation of the effect of small-scale mountains on weather conditions during the May 2021 ultramarathon in Gansu Province, China, Journal of Geophysical Research: Atmospheres (2022). DOI: 10.1029/2022JD036465
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