‘Uncertainties’ cloud forecast accuracy

After giving several false alarms for rainstorms on July 1, the Beijing Meteorological Bureau explained on Sunday that forecasting precipitation comes down to a lot of guesswork.

The bureau issued a thunderstorm and lightning warning at 6:05 am Friday, followed by a rainstorm warning at 7:50 am and then another thunderstorm and lightning warning at 12:35 pm. All were canceled in the end, with no predicted rainfall.

Over 30 flood prevention workers waited for 13 hours on Friday in the Fengyi Bridge area of Fengtai district, one of the areas most vulnerable to flooding in Beijing. They finally left at 8 pm, after it was confirmed that no heavy rain would fall, the Beijing Evening News reported.

With the weather on everyone’s minds, many have expressed unhappiness with the city’s meteorologists.

The bureau should release forecast changes via text message and outdoor public screens, as well as set up a mircoblog to provide real- time information, a Beijing News editorial said on Sunday.

It continued to say that the bureau seldom explains why its forecasts are wrong, and that people deserve to know if the inaccuracies stem from technical limitations or human error.

“Even if the mistake is caused by technical limitations, a mistake is a mistake, and it has brought harm to society. Facing the grievances of the public, someone should step up to take moral responsibility. Is it asking too much [for the meteorological bureau] to sincerely apologize to the public and ask for understanding and forgiveness?” the editorial read.

The bureau’s chief meteorologist Sun Jisong responded that they do alert news outlets and make corrections on their website when the forecast changes, but noted the infeasibility of some of the other suggestions.

“Sending texts and broadcasting the weather outdoors are way beyond our ability,” Sun told the Global Times. He did not know if they would launch a microblog.

As to the request for an apology, Sun would only say, “Anyone can utter his opinion, and I don’t want to comment on it.”

It is common knowledge that weather forecasting has its uncertainties, Sun added.

Beijing Meteorological Bureau director Qiao Lin was quoted by the Beijing Evening News as saying that China’s rainstorm forecast accuracy is nearly 20 percent, slightly inferior to the accuracy rates of the US and developed European countries.

“[The figure of 20 percent] is an estimation based on experience and perception, and there’s no worldwide standard by which to measure rainstorm forecast accuracy,” bureau meteorologist Zhang Yingming explained to the Global Times on Sunday.

According to Zhang, major rainstorms are low-probability events that only happen once or twice a year in Beijing, a city that sees no precipitation almost 80 percent of the year.

Beijing mainly uses radar with a range of up to 250 kilometers to detect cumulonimbus clouds, Zhang said.

“But the clouds can develop and scatter very fast. The actual rain might happen in different places than the analysis that the current radar image suggests,” Zhang said.

“The rainstorms have the characteristics of being very sudden and localized,” Zhang said. Predicting if and where there will be a rainstorm is a worldwide challenge, he added.

As a result of the rarity of rainstorms, the bureau simply does not have enough experience to forecast extreme weather, Zhang explained, adding that the deluge that swamped the city on June 23 was a once-in-a-hundred-years rainstorm. The metrological bureau can predict rain showers with relatively better accuracy, he said.

The storm that was predicted for July 1 did actually happen, just not in Beijing, Zhang added.

“We thought the day of July 1 met the requirements for a storm. And actually, it did happen on July 1, but it happened in Tianjin and Hebei Province, about 100 to 200 kilometers south of Beijing,” Zhang said. “Meteorologically speaking, our forecast was relevant.”

According to the Beijing Meteorological Bureau, today should be sunny, but tomorrow they are predicting overcast weather with thunderstorms.

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