With global warming, regionally extreme cold events also occur occasionally and cause hazards and damages. The Tibetan Plateau, with its high elevation and the unique ecosystem, is one of the most vulnerable regions responding to climate change. In early spring 2019, a cold surge hit the southeastern Tibetan Plateau. The daily life of more than 158,000 people and forage supplies of 1.19 million livestock were affected by the cold event, which resulted in economic losses totaling 100 million Yuan.

"We want to understand such cold events against the background of climate warming in this particular region. Would it happen more often or less often? In particular, what's the role of influence of human activities, technically called anthropogenic forcing?" said Prof. DUAN Jianping from the Institute of Atmospheric Physics at the Chinese Academy of Sciences (IAP), when he explained the motif of his study published in Bulletin of the American Meteorological Society.

DUAN and his co-authors from IAP, Chinese Academy of Meteorological Sciences and Met Office, UK performed the event attribution study for the extreme early-Spring cold surge occurred in the southeastern Tibetan Plateau in 2019.

Snowed covered Biru County, Southeastern Tibetan Plateau. Photo taken on 26 September, 2020 by DUAN Jianping.

The results showed that the core region of the cold event located in 28-35^oN, 90-100.3^oE, where the average daily maximum air temperature (Tmax) during 25 February to 11 March of 2019 is record-breaking since 1966. It was 2.55^oC lower compared to the 1981-2010 climatology. The return period of the 2019 cold event is about once in 34 years, but the model simulations suggest that it could be once every few years if there is no influence of human activity. Without anthropogenic influences, the regionally averaged maximum air temperature of early Spring 2019 in the study area would be 1.9oC lower than the actual.

A formal event attribution analysis based on HadGEM3 developed at Met Office, UK and CMIP6 ensemble simulations indicate that anthropogenic forcing has reduced the likelihood of extreme early-Spring cold event over the southeastern Tibetan Plateau similar to 2019 by about 80%.

"So in this particular region, anthropogenic forcing actually reduces the frequency of such extreme cold events." Concluded Prof. Duan. "The next step will be to see how the decreased frequency of cold extremes in the special region affects the phenology and ecosystem."

This research was supported by the National Natural Science Foundation of China (Grants 41875113), the National Key R&D Program of China (2016YFA0600404) and CSSP.

Reference: Jianping Duan, Liang Chen, Lun Li, Peili Wu, Nikolaos Christidis, Zhuguo Ma, Fraser Lott, Andrew Ciavarella, and Peter Stott. Anthropogenic Influences on the Extreme Cold Surge of Early Spring 2019 over the Southeastern Tibetan Plateau. Bulletin of the American Meteorological Society, 2021, 102 (1): S111–S116.
https://journals.ametsoc.org/view/journals/bams/102/1/BAMS-D-20-0215.1.xml

Media contact: Ms. LIN Zheng, jennylin@mail.iap.ac.cn