Rice harvests are collapsing under more intense flood seasons

Rice feeds more than half the world, yet it grows in a surprisingly fragile way. The crop thrives when fields hold a shallow sheet of water – a thin layer that keeps weeds down and helps stabilizes soil temperature.

But that same strategy becomes a liability when water rises too high or stays too long. A new global analysis shows just how costly that vulnerability has become.

Severe flooding has quietly chipped away at rice harvests for decades, cutting yields by roughly 4.3 percent – about 18 million tons of rice every year – between 1980 and 2015.

That is food that never reached markets, households, or the billions who depend on rice daily.

Climate pressure hits rice hard

The damage from flooding has not stayed steady. The pace has accelerated since 2000 as extreme floods have become more frequent across major rice-growing regions. Researchers warn that climate change is likely to make this trend even worse.

Scientists and farmers have long paid close attention to drought, because dry spells clearly hurt yields.

The study shows that droughts reduced rice yields by an average of 8.1 percent per year during the 35-year period. But it also brings floods into sharper focus as a separate, growing threat.

“While the scientific community has focused on damage to rice yields due to droughts, the impacts of floods have not received enough attention,” said study co-author Steven Gorelick, a professor of Earth system science at the Stanford Doerr School of Sustainability.

“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.”

Measuring when water turns fatal

The team behind the study drew on many types of information at once. They combined data on rice growth stages, annual global rice yields, and a global dataset of droughts and floods that stretch back to 1950.

The researchers added a model of how floodwaters move through river systems and a simulation of soil moisture levels in major rice-growing basins over time.

This mix of records and models allowed them to link specific weather events to changes in harvests.

Rice normally benefits from shallow flooding, especially early in its growth. A thin layer of water can actually help the plant, but the helpful zone is narrow.

Once depths and durations cross a certain line, the water cuts off air and light, and the plants can no longer cope. The study aimed to pinpoint that threshold and measure how often it has been crossed across regions.

What makes a flood deadly for rice

Study lead author Zhi Li pointed out the research clearly defines for the first time what makes a flood deadly for rice crops. A full week underwater during the plant’s growth cycle is the key threshold.

“When crops are fully submerged for at least seven days, most rice plants die,” said Li, who worked on the research as a postdoctoral fellow in Gorelick’s lab at Stanford.

“By defining ‘rice-killing floods,’ we were able to quantify for the first time how these specific floods are consistently destroying one of the most important staple foods for more than half of the global population.”

The analysis also looked ahead. The analysis suggests that in the coming decades, the most extreme week of rainfall in major rice-growing river basins could intensify.

Those peaks may bring about 13 percent more rain compared to the 1980–2015 baseline.

That kind of increase in the heaviest rain weeks means the rice-killing threshold is likely to be crossed more often unless farming systems change.

The world’s riskiest basins

The study points to places where flood-resistant rice varieties and smarter water management could make the biggest difference.

Regions at highest risk include the Sabarmati Basin in India, which experiences the longest rice-killing floods.

Other hot spots include North Korea, Indonesia, China, the Philippines, and Nepal, where the impact from rice-killing floods has grown the most in recent decades. The largest losses overall have been in North Korea, East China, and India’s West Bengal.

The research also uncovered exceptions such as India’s Pennar Basin, where floods appear to enhance rice yields. The authors say hot, dry climates in these regions may explain the pattern, because they allow stagnant floodwater to evaporate quickly.

This pattern shows that the impact of flooding depends not only on depth and duration but also on local background climate and how long water really stays on the fields.

Rice caught in climate whiplash

For Gorelick and Li, the latest findings highlight the importance of understanding how rice yields respond to floods, droughts, heat waves, and cold stress individually and in sequence.

Previous research has shown that sequences of weather whipping from drought to flood and back again result in nearly twice the rice yield loss compared to individual flood or drought events alone.

According to the researchers, how these combined effects can be mitigated remains a major challenge.

Flood-resistant rice varieties, better early warning systems, and infrastructure that can drain or hold water when needed all play a part in reducing risk. So do farming decisions about when to plant and which fields to prioritize.

As heavy rains, dry spells, and sharp swings between them become more common, farms and policymakers will face growing pressure to adapt.

The future of rice may depend on how quickly farms adapt to water that turns from helpful to harmful within days.

The full study was published in the journal Science Advances.

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