Climate change and extreme events in China
Through strong collaboration, scientists from the UK and China are helping advance our knowledge around the influence of climate change on extreme events.
In June 2019, over 6 million people in southern China were impacted by heavy rains which caused flooding and landslides. The extreme event damaged 80,000 houses and affected over 400,000 hectares of crops. In the same year, south-western China experienced a severe drought event due to low rainfall. The event led to over 100 rivers and 180 reservoirs drying out and there were severe drinking water shortages for thousands of people and livestock.
Since 2014, the Climate Science for Services Partnership China (CSSP China) project, supported by the UK Government’s Newton Fund, has been using event attribution to study the role of climate change in extreme events such as these in China. Here we talk to scientists involved in the project about their research.
What is extreme event attribution?
Extreme event attribution investigates the links between the climate and extreme weather. “When extreme events happen, we’re often asked if they were caused by climate change. We can’t answer that question directly, but we can see if human influence on the climate made the event more likely”, says Met Office climate scientist Dr Fraser Lott.
One way to conduct attribution studies is by using climate models. “We first simulate the world as we understand it, with natural and human influences, many times to see the range of possible weather. We usually see the event we’re studying in a few of those simulations. We then make a second group of simulations, this time with only natural climate change from volcanoes and changes in the sun. We’re likely to see the event in some of these simulations too” added Fraser.
By looking at how much more, or less, likely the event is in the simulations with human influence, the scientists can see how much influence climate change had on the chance of that event.
What is the CSSP China project doing?
Led by the University of Edinburgh in collaboration with the China Meteorological Administration, NCAS-Climate, and the Met Office, CSSP China has been training early career scientists from China in extreme event attribution through workshops.
“These workshops are a great demonstration of knowledge exchange. We bring state-of-the-art model data and techniques. The participants nominate the extreme events to be studied and also bring scientific understanding of the weather drivers of the event. And it is great fun to work with so many talented scientists from China and the UK,” explains Prof. Simon Tett from the University of Edinburgh.
The last workshop, held at Sun Yat-sen University, Zhuhai in January 2020, resulted in three papers on extreme events in China being published in the recent Bulletin of the American Meteorological Society special report, Explaining Extreme Events from a Climate Perspective.
Did human driven climate change influence any of the extreme events studied?
One of the studies focused on a severe drought event that occurred between May and June 2019, in southwestern China. Yunnan and western Sichuan were particularly affected by the event and over 640,000 hectares of crops of rice, corn and potatoes were damaged. At the peak of the event, average rainfall was the lowest on record since 1960 for the region and the lack of rainfall impacted the drinking water supply for over 824,000 of people.
Scientists from the project found that human driven climate change increased the likelihood of such an event by a factor of six.
Does climate change always influence extreme events?
Climate change doesn’t always change the probability or intensity of an individual event. Other factors such as natural variability in weather systems can play a big role.
In a study on the extended wet and overcast winter of 2018/2019 in the Yangtze River Valley in China, scientists found that climate change had no influence on the number of excessive rainy days. Instead they found that natural climate variability played a large role.
Have there been any other key findings?
One of the interesting findings from the CSSP China workshops is the influence of climate change on rainfall events of different durations in China. A study led by Wenxia Zhang from the Institute of Atmospheric Physics in China, looked at heavy rainfall events in central western China in 2018. It found that climate change halved the probability of persistent heavy rainfall lasting two to four weeks in the region but increased the likelihood of daily extremes by 1.5 times.
Wenxia explained that this difference was due to the influence of different climate drivers. “For daily extreme rainfall, atmospheric moistening induced by greenhouse gases increased the likelihood. Whereas for persistent heavy rainfall events, the weakened large-scale circulation related to aerosol emissions reduced the probability.”
The results from the present-day study are also not simply comparable to what may be experienced in future, creating challenges for flood adaptation planning. “Both daily and persistent heavy rainfall events are expected to occur more frequently in the region in future”, commented Wenxia.
Another recent study on heavy rainfall events in the mid to lower reaches of the Yangtze River found similar results to the earlier paper. The study was also the first example of a previous workshop participant using their training to study the impact of climate change on extreme events in China.
What has been the impact of the project?
To date, over 30 early career scientists have participated in the workshops and participants from previous workshops have returned as tutors. The outcomes from the CSSP China workshops’ results will be used to provide decision makers with information about how the risks of extreme events have changed due to climate change.
“I really enjoyed the workshop as I learned to collaborate with different people and got long-lasting support from senior scientists which continues even after the workshop finished”, commented Wenxia.
The project is also providing benefits beyond China. Knowledge gained from the project helped develop a workshop to train more early career scientists in extreme event attribution in the Climate Science for Services Partnership Brazil (CSSP Brazil) project. Led by Dr Sarah Sparrow from the University of Oxford, the workshop focused on an extreme rainfall event that impacted over 100 municipalities in Brazil.
“Being involved in running China workshops provided me with a template on how to run and structure a successful workshop event that is not only fun and engaging for the participants, but also for the tutors and workshop leaders involved. In the Brazil workshop we were able to demonstrate that the attribution workshop format developed in the CSSP China projects could be successfully extended into to include additional analysis on the impacts of the extreme rainfall event,” Dr Sarah Sparrow, University of Oxford.
Following on from this, the project is planning to share knowledge to enable these workshops to be used by other projects in the Weather and Climate Science for Services Partnership (WCSSP) programme.
Hu et al. 2021, Was the Extended Rainy Winter 2018/19 over the Middle and Lower Reaches of the Yangtze River Driven by Anthropogenic Forcing, Bulletin of the American Meteorological Society, Explaining Extreme Events in 2019 from a Climate Perspective
Li et al. 2021, Anthropogenic Influences on Heavy Precipitation during the 2019 Extremely Wet Rainy Season in Southern China, Bulletin of the American Meteorological Society, Explaining Extreme Events in 2019 from a Climate Perspective
Lu et al. 2021, Anthropogenic Influence on 2019 May–June Extremely Low Precipitation in Southwestern China, Bulletin of the American Meteorological Society, Explaining Extreme Events in 2019 from a Climate Perspective
Nanding et al. 2020, Anthropogenic Influences on 2019 July Precipitation Extremes Over the Mid–Lower Reaches of the Yangtze River, Frontiers in Environmental Science, 8, 603061
Zhang et al. 2020, Anthropogenic Influence on 2018 summer persistent heavy rainfall in central western China, Bulletin of the American Meteorological Society, Explaining Extreme Events in 2018 from a Climate Perspective