Climate change's impact on rice output

by Arvin Donley
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The severe drought that has devastated crops in Russia this summer serves as a grim reminder of what may lie ahead for agriculture in years to come due to the global climate change phenomenon.

Particularly unsettling is the impact a warmer climate may have on the production of rice — considered the world’s most important crop for ensuring food security and addressing poverty.

A new study by an international team of scientists found that the net impact of projected temperature increases will be to slow the growth of rice production in Asia. Rising temperatures during the past 25 years have already cut the yield growth rate by 10% to 20% in several locations.

Published in August in Proceedings of the National Academy of Sciences, a peer-reviewed scientific journal from the U.S., the report analyzed six years of data from 227 irrigated rice farms in six major rice-growing countries in Asia, which produces 90% of the world’s rice.

It is the first study to assess the impact of both daily maximum and minimum temperatures on irrigated rice production on farmer-managed rice fields in tropical and sub-tropical regions of Asia.

"We found that as the daily minimum temperature increases, or as nights get hotter, rice yields drop," said Jarrod Welch, lead author of the report and graduate student of economics at the University of California, San Diego. "Our study is unique because it uses data collected in farmers’ fields under real-world conditions. This is an important addition to what we already know from controlled experiment settings."

It is estimated that nearly 3 billion of the world’s 6.8 billion people eat rice every day, and more than 60% of the world’s 1 billion poorest and undernourished people who live in Asia depend on rice as their staple food. The researchers said a decline in rice production will cause more people to slip into poverty and hunger.

"Up to a point, higher day-time temperatures can increase rice yield, but future rice yield losses caused by higher night-time temperatures will likely outweigh any such gains because temperatures are rising faster at night," Welch said. "And if day-time temperatures get too high, they also start to restrict rice yields, causing an additional loss in production.

Climate change may have a positive impact on rice production in some areas. For example, a global temperature rise might allow more rice production to occur in the northern regions of China, or growing two rice crops where, until now, only one can be grown per year. But the vast majority of climate change impacts and the overall impact of climate change on rice are likely to be negative.

An International Food Policy Research Institute study forecasts a 15% decrease in irrigated rice yields in developing countries and a 12% increase in rice prices by 2050 as a result of climate change.

"If we cannot change our rice production methods or develop new rice strains that can withstand higher temperatures, there will be a loss in rice production over the next few decades as days and nights get hotter," Welch said. "This will get increasingly worse as temperatures rise toward the middle of the century."

In addition to Welch, members of the research team included: professors Jeffrey Vincent of Duke University and Maximilian Auffhammer of the University of California, Berkeley; Piedad Moya and Dr. Achim Dobermann of the International Rice Research Institute (IRRI); and Dr. David Dawe of the Food and Agriculture Organization (FAO).


IRRI notes that, besides rising temperatures, climate change may also lead to other conditions that could decrease rice production such as: rising sea levels due to melting polar ice shields and glaciers; flooding; salinity; increased carbon dioxide levels; water scarcity; and an increase in pests, diseases and weeds.

Rice is grown in vast, low-lying deltas and coastal areas in Asia predicted to experience the brunt of sea-level rises, making rice one of the crops most vulnerable to climate change. For example, in Vietnam more than 50% of rice production comes from the Mekong River delta, an area that would likely be affected by rising sea levels.

Flooding caused by rising sea levels in coastal areas and the predicted increase in tropical storms due to climate change will likely hinder rice production. At present, about 20 million hectares of the world’s rice-growing area is at risk of occasionally being flooded to submergence level, particularly in the major rice-producing countries of India and Bangladesh.

Rice is unique in that it can thrive in wet conditions where other crops would fail. But uncontrolled flooding is a problem since rice cannot survive if submerged under water for long periods of time.

The salinity associated with higher sea levels will bring salt water further inland and expose more rice-growing areas to salty conditions. Rice is only moderately tolerant of salt and yield can be reduced when salinity is present.

Increases in carbon dioxide levels will also affect production. Higher carbon dioxide levels typically increase biomass production but not necessarily yield.

The threat of drought in rice-producing areas due to climate change is also a major concern. Rainless days for a week in upland rice-growing areas and for about two weeks in shallow lowland rice-growing areas can significantly reduce rice yields. Average yield reduction in rainfed, drought-prone areas has ranged from 17% to 40% in severe drought years. The intensity and frequency of droughts in these regions are predicted to increase due to climate change. Water scarcity affects more than 23 million hectares of rainfed rice production areas in South and Southeast Asia.

The IRRI said that surveys in hundreds of farmers’ fields over the last 10 years show that rice diseases and pests are strongly influenced by climate change as water shortages, irregular rainfall patterns and related water stresses increase the intensity of some diseases, including brown spot and blast. On the other hand, new environmental conditions and shift in production practices could lead to reductions of diseases such as sheath blight or insects such as whori maggots or cutworms. Weed infestation and rice-weed competition are predicted to increase and will represent a major challenge for sustainable rice production.


IRRI, which funded the Asian rice production study along with the FAO and the University of California, San Diego, said it is working to develop rice varieties that can cope better with the conditions predicted to occur and to improve crop management to develop more resilient rice production systems.

IRRI has developed a rice research and breeding program to make rice more tolerant of submergence, drought, heat and salinity — all conditions predicted to increase in frequency and severity with climate change.

Recently, the IRRI developed a submergence-tolerant rice that can still produce good yields after two weeks under water. Varieties with improved drought and salinity tolerance have also been released.

The IRRI said it is making progress toward developing "C4" rice with a supercharged photosynthesis mechanism that is much better at using sunlight to convert carbon dioxide and water into grain. It is believed that C4 rice could yield up to 50% more grain than currently possible from existing rice varieties and be vastly more water and nutrient-efficient.

IRRI said it is also investigating suitable management strategies that farmers and governments can adopt to help rice cope with the effects of climate change.

Establishment and development of efficient irrigation infrastructure, coupled with water-saving techniques, can help make the best use of limited water. Modified cropping patterns, improved nutrient supply and nutrient management strategies adjusted to available water resources, land-leveling and soil improvement may all help rice in times of drought.

Salinity can be managed by improving water harvesting, water management and appropriate choice of cropping patterns. Infrastructure can also be developed to improve drainage and yet restrict intrusion of saline water.

IRRI said it is also preparing for possible shifts in the impacts of different pests by developing more ecology-based pest management approaches to reduce pest damage. These strategies seek to maximize rice productivity by using pest-resistant varieties, gaining a better understanding of pest dynamics and developing more diverse ecosystems to keep pests at acceptable levels with minimum use of pesticides.