The traditional plum rain season has stopped, why is there no more mist and rain in the south of the Yangtze River?

For thousands of years, the plum rains have created the Jiangnan region of China with abundant fish and rice, and have had a profound influence on ink painting and poetry and oriental architecture.

In just over a hundred years, human activities have forced the precipitation during the plum rain season to gradually deviate from its traditional characteristics, resulting in no more mist and rain in the south of the Yangtze River.

Academician Wang Huijun (corresponding author) and Professor Yin Zhicong (first author) of Nanjing University of Information Science and Technology collaborated to publish a research paper titled "Traditional Meiyu-Baiu has been suspended by global warming" in National Science Review. Starting from the conceptual model that summarizes the traditional Meiyu shaping the economy and culture of Jiangnan, an index that can characterize the rich connotation of Meiyu was constructed, which further revealed the scientific fact that human activities have caused the suspension of traditional Meiyu and Meiyu has almost lost its misty rain characteristics. Under the future warming scenario, Meiyu will further move away from its traditional characteristics and enter a "new normal".

1 Jiangnan was once full of mist and rain, which shaped the unique oriental economy and culture

"The rain at the summer solstice is called yellow plum rain, and clothes will be ruined if it gets wet" is from the Western Jin Dynasty's "Yangxian Customs and Local Records". It can be seen that the smoky and humid plum rain climate has existed since ancient times. For thousands of years, the East Asian plum rain (Chinese Meiyu and Japanese Baiu) has profoundly shaped the unique Eastern economy and culture (Figure 1).

Figure 1 Conceptual model of traditional plum rain shaping the economy and culture of Jiangnan

Although plum rain is often associated with mildew, its gentle rain just nourishes rice in the jointing and heading stages. At the same time, plum rain is also conducive to the increase of organic matter and microorganisms, providing sufficient bait for fish and shrimp. The "land of fish and rice" was formed. The misty plum rain has created the tender, sad and sentimental character of the people in the south of the Yangtze River. The literati in the south of the Yangtze River in the past dynasties were happy about the "light rain in the plum season" and placed their sorrow in the "light and misty overcast".

The painting "Viewing the Rain on the West Hill" painted on the Taihu Lake in Suzhou and the gentle and melodious Wu dialect show us the mist and rain that the ancients felt from the audio-visual dimension (Figure 2). Even the aesthetics and functions of the white walls, black tiles and horse-head walls of the Hui-style architecture are greatly influenced by the plum rain.

Figure 2 Ancient Chinese poems with plum rain as a cultural image or theme (above) and "Viewing the Rain on the Western Hills" painted by Ming Dynasty painter Shen Zhou at Taihu Lake in Suzhou (below)

2 The plum rain is not "mold", the plum rain in East Asia gradually deviates from the traditional characteristics of misty rain

In recent years, mist and rain are rare in the Yangtze River Basin and Japan during the Meiyu period. Due to the lack of quantitative methods to describe mist and rain, it is unclear whether the characteristics of Meiyu have changed significantly under the background of climate change. Although many studies have been conducted on the detection and attribution of extreme Meiyu events, mist and rain are not extreme events, so it is difficult to generalize the existing research conclusions to understand the changes in traditional Meiyu.

Academician Wang Huijun's team first constructed a three-dimensional deviation degree of misty rain (D2MR) index and found that the average D2MR in China's Meiyu and Japan's Baiu regions from 1961 to 2023 showed a significant upward trend. This shows that the East Asian Meiyu has gradually lost its traditional misty rain characteristics and the Meiyu is not "mold".

3 Due to human activities, the future will continue to move away

82.5% (75.2–87.2%) of the D2MR variation trend in Meiyu and 81.1% (42.6–96.1%) of the D2MR variation trend in Baiu can be attributed to human activities. Greenhouse gas forcing from human activities is the main factor affecting the change of D2MR, while the influence of aerosols is relatively insignificant. According to the latest projections, the East Asian Meiyu will move further away from its traditional characteristics and enter a "new normal" under the future warming scenario.

The author team from the Center for Basic Science of Climate System Prediction (CCSP) further pointed out: (1) Compared with ancient times, the momentum of human activities has greatly increased. Whether the "traditional suspension of plum rains" is sufficient to promote changes in human social civilization in East Asia and how it will promote it is worth further discussion. (2) East Asia's ecosystems, energy systems, and transportation networks may suffer huge losses due to their inability to adapt to the rapid transition of plum rains to their extreme states in a timely manner, which requires the integration and response of more disciplines and government departments.

For more details, please read the original article

Yin, ZC, Song, XL, Zhou, BT, Jiang, WH, Chen, HP, Wang, HJ, 2024. Traditional Meiyu-Baiu has been suspended by global warming, National Science Review, nwae166, https://doi.org/10.1093/nsr/nwae166