chinese cave, china rainfall history, china monsoon history
Emperor Taizong (r. 626–649) receives Ludongzan, ambassador of Tibet, at his court; painted in
641 AD by Yan Liben (600–673).

Study Links Rainfall to the Fall of Chinese Dynasties

November 08, 2008 08:00 AM
by Denis Cummings
The study of a cave formation in northern China reveals that the strength of monsoons may have played a large role in the rise and fall of Chinese dynasties.

Strong Monsoons, Strong Dynasties

Chinese and American scientists studied a volleyball-sized stalagmite dating to 230 A.D. from the Wanxinag cave in Northern China and determined the strength of monsoon seasons over the last 1,810 years. Matching up those weather patterns to China’s political history, they found that during strong monsoon seasons Chinese society flourished, but weak monsoon seasons often brought about the end of a dynasty.

Stalagmites are formed when water seeps through the ground and enters a cave below; as the water evaporates, its minerals crystallize and create the cave formation. The researchers took over 700 samples from the Wanxinag stalagmite and tested for the level of oxygen-18 isotopes. Higher levels indicate heavy rainfall, while lower levels indicate droughts.

The researchers said that weak monsoons contributed to the decline of the Tang, Yuan and Ming dynasties. “The synchrony between these cultural events and climate change events is really compelling,” Columbia University paleoclimatologist Peter deMenocal told National Geographic. “Climate in many cases acts like the straw that broke the camel's back.”

The most striking example is during the 10th century, when, after centuries of relatively weak monsoons, there was a sharp drop in monsoon strength between 910 and 930. This coincides with the chaotic Five Dynasties and Ten Kingdoms Period of 907-60, when five dynasties fell in rapid succession and 10-12 independent states were formed.

The monsoons became very strong in the late 10th century and remained strong over the next several centuries under the Northern Song Dynasty. The rainfall allowed the cultivation of rice to soar and the estimated population doubled.

The researchers also found that monsoon patterns were consistent with solar cycles and weather patterns in other parts of the world. For example, there was a correlation between a rise of temperature in the West and a rise in monsoon strength; the strong monsoons of the 10th century coincided with the Medieval warm period, while weak monsoons in the 14th and 15th centuries coincided with the Little Ice Age.

However, the relationship between monsoons and global weather factors has changed in the past 50 years, a time of weak monsoons. The researchers attribute this to human activity and the rise of greenhouse-gas emissions.

Reference: Text of the monsoon study


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