Climate change reduces rice quality in China and Japan

According to a Chinese study, the quality of rice has been deteriorating for decades, and the phenomenon is unlikely to slow down over this century

by Matteo Cavallito

 

Weather conditions related to climate change would lead to a deterioration in the quality of rice grown in East Asia. This is reported in a study published in the journal Geophysical Research Letters. The research, by scientists at Normal University in Shaanxi, China, highlighted the key role of rising temperatures by noting the impact of the phenomenon on the nutritional aspects of what remains a staple food for billions of people. And whose demand, the scientists remind, has doubled globally in the past 50 years.

More than three decades of data under review

“Food security is not only related to yield, but also to quality, which is closely related to human nutrition and market value,” the study explains. “Although crop quality is generally controlled by breed genes, climate change also has an important impact. Our findings highlight that food security should consider both yield and quality aspects.” The investigation, recalls a statement from the same university, was based on data collected over 35 years in Japan and China.

 Experts, in particular, looked at the so-called Head Rice Rate (HRR), an indicator that measures the fraction of grains that retain at least 75 percent of their length after milling.

The study analyzed climatic variables to determine those that most influence rice quality, including night and daytime temperatures, average daily temperature, hot days (with temperatures above 30/35 °C), precipitation, relative humidity, solar radiation, cloud cover, diurnal vapor pressure, transpiration, and carbon dioxide concentration. Results showed that nighttime temperatures are the main factor affecting rice quality.

Temperatures are crucial to rice quality

According to the scientists, when these exceed a critical threshold, photosynthesis is reduced and, with it, starch accumulation in the grains decreases with a deterioration in rice quality and an increase in the incidence of broken grains. “Results show a significant decline in high quality rice rate, mainly driven by warm nighttime temperatures when they exceed a critical threshold estimated at 18°C and 12°C in China and Japan, respectively,” the research states.

Moreover, “Climate projections suggest a continuing decreasing trend in HRR under moderate and high emission scenarios by 2100.”

Also important is the effect of daily solar radiation, which has a negative impact on rice quality, as well as reduced precipitation (to which corresponds a lower quality level) and increased diurnal vapor pressure. On average, the researchers go on to explain, rice quality in China records an HHR of 62 percent and has decreased by 1.45 percent each decade. Higher quality (66 percent) is still noted in Japan, but also a more pronounced decline in quality with a 7.6 percent reduction on a 10-year basis.

Quality is expected to keep declining in the future

The dynamics may be different in the future, but the general worsening trend would still be confirmed. Rice quality is expected to decline by 0.5 percent in Japan and 1.5 percent in China between 2020 and 2100 under a low emissions scenario. Under higher emissions, quality loss in China could exceed 5 percent by the end of the century. The situation would be particularly critical in the country’s southern provinces. In these areas adaptation to rising nighttime temperature levels will be a major problem affecting food security and economic stability, the researchers conclude.