The climate is changing. Overwhelming scientific research and evidence have shown this to be the case. While there is still ongoing scientific exploration into climate change, IRRI recognizes two universal trends predicted by all climate change models:
• Temperatures will increase, resulting in more heat stress and rising sea levels, and
• There will be more frequent and severe climate extremes.
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 countries such as China, or growing two rice crops where, until now, only one can be grown per year. Yet, the vast majority of climate change impacts and the overall impact of climate change on rice are likely to be negative.
The International Food Policy Research Institute (IFPRI) report Climate Change: Impact on Agriculture and Costs of Adaptation forecasts that by 2050 rice prices will increase between 32 and 37% as a result of climate change. They also show that rice productivity will reduce by 14% in South Asia, 10% in East Asia and the Pacific, and 15% in Sub-Saharan Africa.
The vast majority of climate change impacts and the overall impact of climate change on rice are likely to be negative
Experts have predicted that, as a consequence of melting polar ice caps and glaciers due to rising temperatures, seawater levels may rise on average by about 1 m by the end of the 21st century.
Rice is grown in vast low-lying deltas and coastal areas in Asia; sea-level rise would therefore make rice production very vulnerable to climate change. More than half of Vietnam's rice produce, for instance, is grown in the Mekong River delta—all of which would be affected by sea-level rise.
Predicting the precise effect of sea-level rise on rice production in vulnerable areas is complicated because the effect goes beyond sea-level rise itself. The entire hydrology of the delta will be affected; sediment discharge and shoreline gradients will change.
Rice is unique in that it can thrive in wet conditions where other crops fail. Uncontrolled flooding is a problem, however, because rice cannot survive if submerged under water for long periods of time. Flooding caused by sea-level rises in coastal areas and the predicted increased intensity of tropical storms with 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 major rice-producing countries such as India and Bangladesh.
Major flooding events are likely to increase in frequency with the onslaught of climate change and rice-growing areas, currently not exposed to flooding, will experience floods.
Salinity is also associated with higher sea levels as this will bring saline water further inland and expose more rice-growing areas to salty conditions. Rice is only moderately tolerant of salt and yields can be reduced when salinity is present.
As with sea-level rises, the effects of salinity can permeate throughout whole deltas and fundamentally change hydrological systems.
Increased carbon dioxide levels and higher temperatures
Increases in both carbon dioxide levels and temperature will also affect rice production. Higher carbon dioxide levels typically increase biomass production, but not necessarily yield. Higher temperatures can decrease rice yields as they can make rice flowers sterile, meaning no grain is produced. Higher respiration losses linked to higher temperatures also make rice less productive.
The different predictions for elevated temperature, carbon dioxide levels, changes in humidity, and the interactions of these factors make forecasting future rice yields under these conditions challenging. IRRI research indicates that a rise in nighttime temperature by 1 degree Celsius may reduce rice yields by about 10%.
Rice requires ample water to grow. 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, leading to production losses and food scarcity.
With the onset of climate change, the intensity and frequency of droughts are predicted to increase in rainfed rice-growing areas and droughts could extend further into water-short irrigated areas.
Water scarcity affects more than 23 million hectares of rainfed rice production areas in South and Southeast Asia. In Africa, recurring drought affects nearly 80% of the potential 20 million hectares of rainfed lowland rice. Drought also affects rice production in Australia, China, USA, and other countries.
Pests, diseases, and weeds
Surveys in hundreds of farmers’ fields over the last 10 years show that rice diseases and pests are strongly influenced by climate change. 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 shifts in production practices that farmers may adopt to cope with climate change could lead to reductions of diseases such as sheath blight or insects such as whorl maggots or cutworms. As such, new crop health dynamics are emerging.
Weed infestation and rice-weed competition are predicted to increase and will represent a major challenge for sustainable rice production. Also, extreme weather events have recently led to dramatic rodent population outbreaks in Asia due to unseasonal and asynchronous cropping.