Impact of climate change on rice
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.
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.
The challenge for rice production
Global climate change has potentially grave consequences for rice production and, consequently, global food security. Land-use systems in most developing countries are highly vulnerable to climate change and have little capacity to cope with its impacts. Conditions for rice farming will deteriorate in many areas, through water shortages, low water quality, thermal stress, sea-level rise, floods, and more intense tropical cyclones. 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 price as a result of climate change by 2050.
Moreover, flooded intensively managed rice systems release large amounts of methane, but also sequester carbon in soil organic matter, whereas more diversified rice-based cropping systems release less methane, but more nitrous oxide and carbon dioxide. Africa is expected to be very vulnerable to erratic weather patterns arising from climate change, but most disconcerting is that more than half of the growth in Asian rice production over the past decades came from the ‘delta countries’, such as Vietnam and Bangladesh—precisely the countries most vulnerable to sea-level rise and climatic extremes. Many unique ecosystem services in wetland rice culture are now under threat from increasing water scarcity, further aggravated by climate change. What will change in these systems if farmers diversify cropping or switch to ‘aerobic’ water management? Will these systems be resilient and productive enough over the longer term? What will be the sustainable rice-based cropping systems and crop management practices of the future?
The impacts that climate change will have on rice production will play a key role in determining food security in large parts of the world. Especially in Asia, where rice is the staple food of many rural and urban poor, negative effects on yields and availability of rice will directly translate into major food shortages. Consequently, rice is a widespread farming system in many environments considered to be ‘hot spots’ of climate change impacts. For example, sea level rise causing flooding and salinity intrusion may affect Asia’s mega-deltas (Ganges-Brahmaputra in Bangladesh; Irrawady in Myanmar; and Mekong and Red River in Vietnam) limiting future production. This in turn, along with other climate change impacts will affect domestic rice markets as well as international trade.
Moreover, rice is also grown in rainfed lowland regions that are prone to drought and flood. In these areas, production risks will increase under aggravating climatic extremes. Rice yields will also be negatively affected by higher night-time temperatures (a decline of 10% for every 100 C temperature increase).
Alternately, rice production is a source of greenhouse gas (methane) due to flooding of paddies. Like other cropping systems, rice fields also emit nitrous oxide due to soil and fertilizer nitrogen. Flooded rice fields also store large amounts of soil carbon that would be released as carbon dioxide in case rice paddies are converted to upland cropping systems. Under the Global Rice Science Partnership (GRiSP), impacts as well as possible adaptation and mitigation strategies will be studied in synergy and close linkage with other CGIAR research programs.
Climate change: Adaptation and mitigation
Developing rice varieties adapted to climate change
IRRI has a comprehensive rice research and breeding program to make climate-ready rice varieties that are more tolerant of submergence, drought, heat, and salinity—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 around 110,000 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 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 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 a 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.
Reducing emissions from rice
Although rice production is predicted to be affected by climate change, rice farming can also contribute to climate change. Despite 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 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 oxide.
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 determine if fertilizer applications are necessary, what nutrients are needed, and what application time is optimal.
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
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 gases.
Climate change-ready rice
IRRI is developing rice varieties that can withstand conditions forecast to become more frequent and intense with climate change including drought, flood, heat, cold, and soil problems like high salt and iron toxicity.
Environmental stresses constrain rice production, affecting about 30% of the 700 million poor in Asia alone, who live in rainfed rice-growing areas. These stresses can be caused by extreme climatic changes like drought, flooding, or rising sea levels, while some can be inherent like high iron toxicity in the soil. Our breeding programs aim to develop rice types that can survive in these harsh environments.
IRRI breeders use a breeding method known as marker-assisted breeding. It helps breeders incorporate specific desirable traits into new varieties with more accuracy and speed.
In recent years, IRRI has developed rice with better tolerance to drought, submergence, cold, salinity, and sodicity. Our national research and agricultural extension partners test these breeding lines in different locations and countries, including evaluating their performance on farmers’ fields. The selected lines which survive under stress and retain desirable grain qualities are either released directly or bred into widely grown and popular local varieties.
Along with improved crop management, proper use of technology through extension work, and the support of national institutions, these improved varieties or “climate change-ready rice” are showing substantial, positive impacts in the lives of poor farmers.