A persistent south-north flow of the Jet Stream has dredged moisture up from the Indian Ocean, India and Bangladesh and deposited it in a deluge that has persisted over Sichuan, China for at least the past five days. Rainfall in many areas were the worst seen since weather records began in 1954. In one example, the city of Dujiangyan experienced 37 inches of rainfall over the course of 40 hours.
The floods forced nearly 100,000 people to evacuate and have impacted at least 2 million people across the region. Over 200 people are feared dead or missing. With some towns buried under as much as 20 feet of water, thousands of homes and buildings have been destroyed or damaged with transportation brought to a stand-still in many of the effected regions. In hard-hit Dujiangyan, a local resort was buried when a hillside collapsed, burying the area to tree-top level in mud and debris and spurring the evacuation of 352 tourists. Raging floodwaters also caused a nearby bridge collapse that sent at least six vehicles into raging flood waters.
In the video below, provided by KIDgrownup, we can see the raging floodwaters washing away buildings and heavy equipment as people flee the disaster site:
Changed Jet Stream Causes Dangerous, Persistent Weather Pattern as Super Typhoon Approaches
A dwindling, but still significant, number of media sources continue to claim that we cannot attribute single events such as the most recent Sichuan Floods to climate change. Unfortunately, this claim is simply untrue. Climate is a measure of weather over a given area during a long period of time. As climate changes so does the weather. In Europe, for example, major flood events are now twice as likely as they were forty years ago. This 100% increase in floods can be directly attributed to changes in Europe’s climate and, as such, fully 50% of each new major flood is, therefore attributable to climate change. And the fact that the most extreme floods are getting more extreme can also be attributed to climate change. In this case, saying a single record flood event, like the current Sichuan flood, cannot be attributed to climate change is at least 50% untrue. Would a flood like this have occurred, eventually, if climate hadn’t changed? Probably. But it likely would have happened 50, 100, 200 years or more later. Would it have happened this year, the way it did, without climate change? Absolutely not.
At the micro level, we can also look at weather patterns and clearly point out how they are not normal and how they’ve changed as a result of human-caused climate impacts. In the example of this week’s Sichuan Floods, the Jet Stream created conditions where heavy rains, so far, have stalled over Sichuan to inundate the region.
(Sichuan Floods, July 8. Image source: Lance-Modis)
In the above image we can see a thick blot of clouds hovering over Sichuan in Central China. This dense band of clouds is the result of a cut off upper air flow of the Jet Stream forming a strong, persistent upper level disturbance. To the south, we can see a broad band of clouds and moisture being drawn into the system from the Indian ocean and over India, Bangladesh, Thailand and Vietnam. To the east, a tropical system in the Korean Sea also contributes moisture to feed this large storm.
What is most unusual about this particular weather pattern is that it doesn’t move. And we can see this when we switch to today’s Lance-Modis shot. The below image is 4 days later than the July 8 shot. But the storm over Central China has hardly budged.
(Sichuan Floods July 11. Image source: Lance-Modis)
In this shot, the cut off upper level flow in the Jet Stream remains, the dense cloud pack over Central China remains, the strong upper level low remains, and the moisture flow from the Indian Ocean and related regions remain. Ominously, the only marked difference in this shot is the looming approach of super typhoon Soulik from the China Sea. This major typhoon packs winds in excess of 140 miles per hour and could cause severe damage to Taiwan. However, it’s the ability of this system to deliver moisture into an already moisture rich upper level air flow that may result in even worse conditions for Eastern and Central China over the next few days as the storm is projected to make landfall in Eastern China, then track as far as 200 miles west of Shanghai. At this point, some weather models, including the ECMWF ensemble, show Soulik getting absorbed by the cut-off upper level low now parked over China. Were this to happen, the resulting rain event could be far more substantial than even the record floods seen over the past few days.
The Climate Change Link To Extreme Weather
So how did climate change create the conditions in which this dangerous situation emerged?
- The upper level Jet Stream was caused to meander due to a climate change induced loss of sea ice and summer snow cover.
- These changes resulted in a slower progression of weather patterns and more cut-off upper level disturbances.
- The added atmospheric heat content added both moisture and instability, adding fuel for storms like this one.
- Increased ocean temperatures made moisture and heat delivery from ocean systems and tropical cyclones more likely.
Without these conditions, the Sichuan floods were unlikely to have happened with such force, violence and to have been so persistent and long-lasting. And now, a bad situation is made worse via the ocean delivery of a super typhoon, just one of many more frequent storms to plague this region over the last 40 years. An increased frequency a recent scientific study also attributes to climate change.
Hybrid rain superstorm to form over China? Hopefully, not. But, at this point, things aren’t looking too good.