At 6 pm on Sept 5, an hour before the start of a promotional event for the men's soccer final at the 14th National Games, the rain that had started in the afternoon was still falling.

　　Forecasters in Weinan, Shaanxi province, where the final would be played two days later, were staring at radar images to monitor the amount of rain they could expect that evening.

　　They also mulled the guidelines in a document about emergency weather plans for the games, which advised that events could be affected if the precipitation level reached 10 mm an hour.

　　Wu Linrong, deputy head of the Weinan Meteorological Service, said the team's forecasts were crucial to decision-makers at the games.

　　"Too much rain would cause the ball to slide and affect the players on the outdoor pitch during the promotional event. We had to provide accurate forecasts so the organizers and technicians could decide whether to suspend or delay it," he said.

　　Eventually, the event went ahead after the forecasters predicted that the hourly precipitation level would be about 8 mm, lower than in the emergency plan.

　　In the final, on Sept 7, the Shaanxi team won the title by beating a team from the southwestern municipality of Chongqing.

　　Influence of conditions

　　This year, the games featured 35 competitive sports, with events taking place across Shaanxi. They opened on Sept 15 and closed on Monday, but some events had already been completed before the opening ceremony, including the men's soccer, men's volleyball and the diving competitions.

　　"Meteorology and sports are inseparable," said Cai Xinling from the Shaanxi Climate Center.

　　"In the worst conditions, bad weather such as rainstorms and extremely high temperatures could cause outdoor events to be suspended. Other factors, including wind and humidity, could also have an impact on venues and the athletes' performances," she said, adding that wind can be highly influential in certain competitions.

　　"For example, in events such as the javelin and discus, a light head wind can increase lift, which is beneficial to performances. Tail winds are conducive to hammer throwing, while crosswinds can affect accuracy in archery and shooting events."

　　She noted that humidity levels had to be within a set range because too much water vapor in the air could make it difficult for the athletes to breathe easily and perform well, but if conditions were too dry, the competitors may have become dehydrated.

　　Rain affects different sports in different ways. "For track and field events, rain makes the track slippery and hard to run on. But for marathons, a little rain can make the runners feel comfortable and even relieve their nervous tension," Cai said.

　　In the emergency plan, a precipitation level of more than 5 mm was deemed unsuitable for marathon runners, while the limit for track and field venues was slightly lower, at 3 mm.

　　"Conditions we may consider normal are highly influential for sporting events that are sensitive and vulnerable to weather risks," said Luo Hui, deputy head of the Shaanxi Meteorological Bureau.

　　She added that the forecasters needed to take more details into consideration than many people may have realized.

　　"For example, on windy days, we provided information to suggest reinforcing the equipment at venues. On rainy days, even those with just a little precipitation, we needed to remind organizers to prepare rainproofing for spectators and shelters at the ticket checking points," she said.

　　In August 2019, a meteorological center established specifically for the games and comprising 65 staff members from across the province began operations in Xi'an, Shaanxi's capital.

　　The team was supported by the work of other forecasters in the province and by the National Meteorological Center.

　　The experts provided hourly weather forecasts for the organizers and athletes on the day before the games began.

　　Challenges, techniques

　　However, challenges remained: For some events, the forecasters needed to practice new techniques, while the venues were scattered across Shaanxi, which meant that predicting the weather was a very complicated business.

　　Wu, from the Weinan Meteorological Service, said that for the beach volleyball games, the forecasters measured the temperature of the sand for the first time, but they had to overcome technical difficulties to improve their accuracy.

　　"Sand hotter than 45 C burns players, so reports on sand temperatures were a great focus of attention," he said.

　　Initially, the sand was placed on a lawn in the sun so the temperature could be gauged, but the results were inaccurate by between 2 and 6 C. The forecasters realized that the lower temperature of the grass base was affecting the accuracy of the readings. In response, they placed sensors at each of the four corners of the playing area and began recording more accurate temperatures.

　　Meanwhile, a special climate work group formed by the Shaanxi Meteorological Bureau conducted background analyses of weather conditions at sports fields across the province. The team combed through provincial climate data related to the month of September over the past 30 years and calculated the frequency and locations of notable weather events.

　　Mao Mingce, deputy director of the Shaanxi Climate Center, said the facility provided forecasts for every venue so emergency plans could be formulated.

　　For example, Shaanxi's northern areas often experience strong winds and high temperatures, while the south of the province regularly sees heavy rains that can result in landslides and floods.

　　"We had to make proper forecasts that neither exaggerated nor underplayed the situation, so the organizers didn't overwork their plans or neglect risks," Mao said.

　　"In the national games, the forecasters were like sentinels: our major responsibility was to provide information as accurately as possible."

　　Team members from the Shaanxi Meteorological Bureau install equipment to ensure smooth proceedings during the torch-lighting ceremony in Yan'an, Shaanxi province, for the 14th National Games. CHINA DAILY

　　A member of staff at the meteorological bureau in Ankang, Shaanxi, repairs and cleans a water temperature sensor. CHINA DAILY

　　A worker adjusts meteorological equipment while a game of basketball is played at the national games. HU JIANGBO/FOR CHINA DAILY