Extreme rainfall is taking a toll on China's rice crops, and it could get much worse

Extreme rainfall has cut China’s rice yields by 8 per cent over the past two decades, according to a study led by Chinese researchers.

The study, published in the peer-reviewed journal Nature Food on May 4, found that the impact of extreme rainfall on rice yields was comparable to that of extreme heat.

The researchers predicted that by the end of this century, extreme rainfall could reduce rice yields by another 7.6 per cent in China, in addition to other climate change-induced impacts, such as global warming and rising carbon dioxide emissions.

Jian Yiwei, lead author of the study and a PhD candidate at Peking University, said extreme events were projected to be more intense in the future, which would pose an increasing threat to agricultural productivity.

“The aim of our study is to help people better understand extreme events – how do they affect crop production and what scientific and effective measures can be taken when extreme rainfall occurs,” she said.

Scientists are learning more about the impact of extreme weather events on food security.

According to the sixth Synthesis Report from the UN Intergovernmental Panel on Climate Change (IPCC) in March, over the last 50 years, climate change has likely slowed growth in agricultural productivity across the globe.

It has led to food insecurity in parts of Africa, Asia, Central and South America and other vulnerable regions, according to the report.

China, one of the most populous countries, has begun to see the negative impacts of global warming in rising sea levels, severe weather events and melting glaciers.

The Ministry of Water Resources predicted in March that China’s southern region – now in its annual flood season – would suffer from frequent flooding and droughts this year, with some areas experiencing more severe extreme events compared to normal.

Aside from the threats of climate change, concerns over food security in China have arisen over deteriorating relations with the United States and its allies – many of which are major agricultural suppliers.

Chinese President Xi Jinping said at the annual central rural work conference in December that agriculture was the foundation of national security and weak links – including low productivity – must be fixed.

Previous studies had focused mainly on the impacts of drought and extreme heat on crop yields, but relatively little research had been done on the impact of extreme rainfall, Jian said, adding that the impact on the yields remained largely uncertain.

Past studies have usually analysed daily or seasonal rainfall data in county-level or city-level administration zones to evaluate the impact of extreme rainfall, but the method can miss negative impacts, according to the authors.

“Extreme rainfall may occur in a few hours. If you average it out over a whole day or over a whole week, the impact may be invisible,” Wang Xuhui, study lead author and a researcher at Peking University, said.

In their study, the researchers investigated the impact of extreme rainfall on rice yields and discovered two new underlying mechanisms.

The authors used hourly rainfall data collected from nationwide observations and found that yield reductions caused by extreme rainfall were comparable to those due from extreme heat, and were larger than the reductions related to drought, extreme cold and other extreme events.

“This differs considerably from previous findings that indicate that temperature has the dominant role in determining climatic impacts on crop yields, with precipitation having a more minor role,” Jonathan Proctor, a researcher at Harvard University who was not involved in the study, said in a separate article in the same issue of Nature Food.

To reveal more about how extreme precipitation cut down rice yields, the authors conducted 64 rainfall control experiments between 2018 and 2019.

They found that extreme rainfall diminished rice yields in China by reducing available soil nitrogen and physically damaging the branch clusters at the top of rice plants, known as panicles, which make it more difficult for the pant to produce grains.

Wang said people used to think of the effects of climate change as rising temperatures, but “the impacts of climate change are not just warming and rising sea levels”.

“It also includes extreme events, including an increase in the frequency and intensity of extreme rainfall events.”

“These findings demonstrate that it is critical to account for extreme rainfall in food security assessments,” the authors said in the study.