Lately, it seems that Beijing has been experiencing quite a range of weather conditions. Dust storms, sudden temperature declines, snow, hail, and a relentless barrage of wind! WeChat is constantly updating, sending out alerts and warnings for almost every type of weather imaginable. Disastrous conditions! The most powerful winds seen in 70 years! And so forth.
What's going on?
Continue reading for a brief overview of the factors influencing Beijing's unusual weather patterns.
Beijing's Geography and Climate
As many of us are likely aware, Beijing is situated in a topographical bowl, bordered by the Yan Mountains to the northeast, and the Jundu Mountains and Western Hills to the northwest, which extend down along the city's western edge. To the south and east, the city opens up to the vast and flat North China Plain, and further southeast beyond the plain, you find the Bohai Sea. To the west lies the Gobi Desert, while to the west and north of the mountains surrounding Beijing is the Mongolian Plateau.
This geographical layout plays a significant role in the usual weather patterns we recognize. The encircling mountains trap pollution within the "bowl" until it is dispersed by northerly and northwesterly winds. Dust storms are particularly common in April and May. January typically marks the coldest month, while July and August are the hottest.
Beijing experiences a mixed semi-arid, continental monsoon climate. Winters are dry and summers humid. From October to March, cold, dry winds from Siberia descend over the Mongolian Plateau, through the mountains, and into Beijing. However, due to the "bowl" effect, the city usually remains warmer than surrounding regions. The area's mainly northwesterly air circulation diminishes any oceanic climate effects that might be anticipated because of Beijing's proximity to the Bohai Sea. During the summer, hot and humid air flows into the city from the southeast, which is when most of the precipitation occurs, although it varies each year.
Spring and fall are generally the most enjoyable seasons, although they are relatively short. Fall is clear and picturesque, while spring is also pleasant but tends to be the windiest season, known for the aforementioned dust storms.
April Wind Event
The recent wind event in mid-April was caused by a cold vortex moving in from Mongolia. The city issued its first-ever orange-level gale alert due to strong winds and rapid gusts, along with noticeable temperature drops. According to China's wind speed scale, which ranges from level 1 (weakest) to level 17 (strongest), gusts from this cold vortex were estimated to be between levels 11 and 13, with outer districts experiencing the strongest winds.
What is a Cold Vortex?
A cold vortex shares some characteristics with a polar vortex, but they are distinct phenomena. A cold vortex is a low-pressure system that leads to temperature decreases and often brings increased precipitation; it is smaller, lower, and more variable than a polar vortex. Typically, a cold vortex impacts a specific area and is temporary.
Spring, being a transitional phase in Beijing’s seasonal cycle, naturally brings a mix of weather conditions. The occurrence of the cold vortex in April intensified the usual weather patterns, transforming the anticipated spring weather into something resembling meteorological chaos.
So, Why is it So Windy?!
This phenomenon can be attributed to the narrow tube effect, which occurs when wind speed increases as air moves through a confined space. For Beijing, the mountain passes that have historically been significant for trade and communication routes between the North China Plain and regions beyond the mountains, including the Mongolian Plateau, create these constricted areas that substantially boost wind speed. This explains why warnings were more severe for the northern and western outer districts, as they are closer to or situated in the mountains.
Next time, impress your friends by mentioning the "narrow tube effect"!
China's Weather Warning System
China implements a four-color tiered warning system for various weather events. Although the specific weather criteria for triggering each tier differ depending on the phenomenon, the warning colors remain consistent. From most to least severe, the colors are red, orange, yellow, and blue. The orange gale alert issued in April was the second most severe warning for gale conditions.
Looking back, China's weather alert system bears striking similarities to the notoriously criticized Bush-era US Homeland Security Advisory System, just missing the low-risk green. More than two decades after that system's initiation, it's fair to say that China's weather alert framework is significantly more logical.
A (very) short investigation into the causes of Beijing's unusual weather.
