Severe Floods Slash Global Rice Yields, Impacting Food Security

Severe flooding has significantly reduced global rice yields, threatening the food security of billions who rely on this staple. Research from Stanford University, published in Science Advances, indicates that between 1980 and 2015, rice production suffered losses of approximately 4.3%, or 18 million tons, per year. The frequency of extreme flooding in major rice-growing regions has increased since 2000, a trend expected to worsen due to climate change.

While the adverse effects of droughts on rice yields have long been documented, the new study sheds light on the impacts of floods, which have not received adequate attention. The research underscores that droughts resulted in an average yield reduction of 8.1% per year during the same period. However, excessive flooding during critical growth stages can devastate rice crops.

According to Steven Gorelick, senior co-author of the study and professor at the Stanford Doerr School of Sustainability, the scientific community has largely overlooked the damage caused by floods. He stated, “Our research documents not only areas where rice yields have suffered due to past flooding, but also where we can anticipate and prepare for this threat in the future.”

Understanding Flood Impacts on Rice Cultivation

The study introduces a new definition of what constitutes “rice-killing floods.” Lead author Zhi Li, who conducted the research as a postdoctoral fellow at Stanford and is now part of the faculty at the University of Colorado Boulder, explained that a full week of submersion during the plant’s growth cycle is critical. “When crops are fully submerged for at least seven days, most rice plants die,” Li remarked. This study quantifies how these specific flooding events consistently threaten one of the most vital food sources for over half of the global population.

To evaluate the damage caused by droughts and floods, researchers analyzed rice growth stages, annual global rice yields, a comprehensive dataset of droughts and floods since 1950, flood dynamics models, and simulations of soil moisture levels across major rice-growing basins.

The findings suggest that in the coming decades, the most extreme week of rainfall in major rice-growing river basins could see an increase of 13% compared to averages recorded from 1980 to 2015.

Potential Solutions and Regional Impacts

Increasing the adoption of flood-resistant rice varieties presents a viable strategy to mitigate future losses, particularly in regions most vulnerable to rice-killing floods. Areas such as the Sabarmati Basin in India, known for enduring lengthy floods, along with countries like North Korea, Indonesia, China, the Philippines, and Nepal, are identified as high-risk zones where the impacts of flooding have escalated in recent decades.

Notably, the largest losses in rice yields have been observed in North Korea, eastern China, and the West Bengal region of India. Interestingly, exceptions exist, such as in the Pennar Basin of India, where floods appear to enhance rice yields, potentially due to the region’s hot, dry climate that allows for quick evaporation of stagnant floodwaters.

Researchers emphasize that understanding how rice yields respond to floods, droughts, heat waves, and cold stress, both individually and in combination, is crucial. Previous studies indicate that sequences of weather events shifting from drought to flood can cause nearly double the yield losses compared to isolated events.

The authors conclude that addressing the cumulative effects of these environmental factors remains a significant challenge for global food security. As climate change continues to exacerbate extreme weather events, ensuring the resilience of rice production will be critical for feeding billions worldwide.