Thursday, May 5, 2011

• Temperatures will increase, resulting in more heat stress and rising sea levels, and
• There will be more frequent and severe climate extremes.

Rice plays a central role in feeding more than 3 billion people, including most of the world’s 1 billion poor, and any significant negative effect on rice production caused by climate change would be devastating for efforts to achieve global food security and address poverty.

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.

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

The impact of climate change on rice

Sea-level rises

Recent predictions suggest that, as a consequence of melting polar ice shields and glaciers and 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 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 is grown in the Mekong River delta - all of which would be affected by sea-level rises.

Predicting the precise effect of sea-level rises on rice production in these areas is complicated because the effect goes beyond the basic sea-level rise itself. The entire hydrology of the delta would be affected, including changes in sediment discharge and shoreline gradients.

Flooding

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

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%.

Water scarcity

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.

Adapting rice to climate change

IRRI’s approach to help rice production in the face of climate change is 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.

Developing rice varieties adapted to climate change

IRRI has a comprehensive 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.

A recent major advance in this area has been the release of IRRI’s submergence-tolerant rice that can still produce good yields, even after two weeks under water - conditions that would devastate most other types of rice. Varieties with improved drought and salinity tolerance have also been released and work continues to improve their yield even when under stress caused by these conditions.

IRRI uses the International Rice Genebank - the most comprehensive collection of rice genetic diversity in the world with more than 109,000 different types of rice - as a source of rice genes associated with traits that help rice cope with climate change. Modern science is finding beneficial genes from this diversity and incorporating them into high-yielding rice varieties more accurately and faster than ever before. Genetic diversity outside of rice can also be used to improve the properties of rice through genetic modification.

IRRI is making progress towards developing “C4” rice - rice with a supercharged photosynthesis mechanism that is much better at using sunlight to convert carbon dioxide and water into grain. C4 rice could yield up to 50% more grain than currently possible from existing rice varieties. Importantly, in relation to climate change, it would be vastly more water- and nutrient-efficient.

Management strategies to cope with climate change

IRRI 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.

In the case of flooding, proper seed and seedbed management practices, direct seeding, and optimal fertilizer use can help to have taller, healthier, less flood-susceptible plants that also recover better after flood exposure. Growing rice in the dry season, when floods are unlikely to occur, is also an option with potential in many regions.

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, thereby reducing the impact of salinity.

IRRI 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 smarter understanding of pest dynamics, and developing more diverse ecosystems to keep pests at acceptable levels with minimum use of pesticides.

Reducing the impact of rice on climate change

Although rice production is predicted to be affected by climate change, rice farming can also contribute to climate change. In spite of its fairly minor contribution on a global scale, rice production is a substantial source of greenhouse gases at the national scale in many Asian countries. Combining water-saving and nutrient management technologies can maintain yields and reduce greenhouse gas emissions from rice fields, while simultaneously reducing costs and conserving valuable inputs. And, smart management of rice residues and reducing the cooking time of rice can also help reduce the impact of rice on climate change.

Reducing methane emissions

Rice is often grown in flooded fields under anaerobic soil conditions that release methane as organic matter decomposes in the soil. Methane is a greenhouse gas that is about 25 times more potent than carbon dioxide. Methane accounts for about 20% of the enhanced greenhouse effect and rice contributes about 10% of this.

IRRI’s research shows that growing rice in flooded fields has proven to be a highly sustainable practice where soil health can be maintained. Irrigated rice fields have been an integral part of rice production in Asia for centuries and they are responsible for 75% of global rice production.

Water-saving technologies such as alternate wetting and drying reduce the amount of time rice fields are flooded and can reduce the production of methane by about 60-90%. IRRI is promoting alternate wetting and drying as an alternative management practice.

Reducing nitrous oxide emissions

Practices such as alternate wetting and drying that reduce methane emissions can, however, increase the production of nitrous oxide, another greenhouse gas, which is 300 times more potent than carbon dioxide. The presence of excess nitrogen in the soil, combined with ‘unsaturated’ fields, produces nitrous

To mitigate the production of nitrous oxide, water-saving technologies must be accompanied by good nutrient management. Reducing fertilizer wastage - hence the amount of excess nitrogen in the soilreduces nitrous oxide emissions. IRRI helps farmers manage their nutrients through tools such as the Nutrient Manager, an online resource to help determine if fertilizer applications are necessary, what nutrients are needed, and what application time is optimal.

Rice residues

After rice is harvested and dehusked, rice straw and rice husk residues remain. These residues are commonly incorporated back into the soil or burned. When incorporated, methane is produced as decomposition occurs under waterlogged conditions; when burned,, methane and soot develop and contribute to climate change.

Charring - or partly burning - rice residues and adding the obtained black carbon or “biochar” to paddy fields instead of incorporating untreated harvest residues may reduce field methane emissions by as much as 80%. In addition, the black carbon is highly stable - meaning the carbon can be effectively stored in the ground for potentially hundreds or thousands of years. As an added bonus, black carbon can improve the fertility of degraded soils.

Biochar can be the byproduct of bioenergy production from rice residues, which adds the additional advantage of energy generation. For rice husk, the respective technologies are already advanced, but little is known on the use of straw. IRRI is looking at ways to overcome the practical challenges in collecting and charring rice residues at the farm or village level to help farmers take advantage of this technology.

Rice cooking time

Everyday, millions of households cook rice and in so doing consume energy, which usually results in the emission of greenhouse gases. The cooking time of rice is determined by the temperature at which the crystalline structures of the starch begin to melt - the gelatinization temperature. Rice with low gelatinization temperature takes a short time to cook and rice with high gelatinization temperature takes longer.

IRRI is exploring whether a recently discovered gene that affects gelatinization temperature could allow rice varieties with lower gelatinization temperature to be bred. If achieved, this could decrease average rice cooking time by up to four minutes.

A decrease in four minutes of cooking time for each time rice is cooked worldwide could save more than 10,000 years of cooking time everyday, resulting in massive global energy savings and reduced emissions of greenhouse.