Intense flooding has reduced global rice harvests by an average of 4.3% annually between 1980 and 2015, according to a new Stanford University study. The research highlights that a week of full submergence kills most rice plants, making floods a greater threat than previously recognized. Climate change is expected to worsen these impacts in key rice-growing regions.
A study published on November 14 in Science Advances reveals that extreme floods have caused significant losses in global rice production, averaging 18 million tons per year from 1980 to 2015. Researchers from Stanford University found that these losses have intensified since 2000, coinciding with more frequent extreme floods in major rice-growing areas. Droughts, meanwhile, reduced yields by 8.1% annually over the same period.
The team defined 'rice-killing floods' as those causing full submergence for at least seven days during the plant's growth cycle, a threshold that leads to the death of most rice plants. 'When crops are fully submerged for at least seven days, most rice plants die,' said lead author Zhi Li, a former postdoctoral fellow at Stanford who recently joined the University of Colorado Boulder.
Using data on rice growth stages, global yields, historical floods and droughts since 1950, flood behavior models, and soil moisture simulations, the researchers quantified past damages and projected future risks. They estimate that the most intense week of rainfall in key basins could increase by 13% compared to the 1980-2015 baseline, potentially making rice-killing floods more common as the climate warms.
High-risk regions include India's Sabarmati Basin, which experiences the longest such floods, as well as North Korea, Indonesia, China, the Philippines, and Nepal, where flood impacts on yields have grown most. The greatest total losses occurred in North Korea, East China, and India's West Bengal. An exception is India's Pennar Basin, where flooding sometimes boosts yields due to quick evaporation in hot, dry conditions.
'While the scientific community has focused on damage to rice yield due to droughts, the impacts of floods have not received enough attention,' noted senior co-author Steven Gorelick, a professor of Earth system science at Stanford's Doerr School of Sustainability. The study calls for wider adoption of flood-resistant rice varieties to mitigate future losses, especially amid compounding stresses like heat waves and rapid weather swings, which can nearly double yield reductions.