Biological vulnerability to climate change
The impacts of climate change on rice production and productivity can be summarized by the following factors: heat stress, increased night-time temperature, flooding, drought and salt stress.
Rice is a tropical crop. It can withstand high temperatures, but unfortunately also rice has its limits. During the vegetative stage rice can withstand night temperatures up to 25 °C and day temperatures up to 35 °C. Higher temperatures will result in reduced photosynthesis.
Another phenomenon related to high daytime temperatures is heat stress. Heat stress causes spikelet sterility, eventually leading to high yield loss. Rice is particularly sensitive to heat stress at the flowering stage, which may occur when the temperature rises above 35 °C.
Especially, the time of day when rice opens its flower is very important, because it is at that moment that rice is most vulnerable to high temperatures. The fact that African rice (Oryza glaberrima) flowers early in the morning, while Asian rice (Oryza sativa) flowers just before noon, unleashed the search for the African rice early flowering trait that enables the rice flower to escape the heat of the day.
The effect of increased CO2 on rice yield is not yet fully understood. It is generally thought that the positive effects of increased CO2 levels, or CO2 fertilization, will disappear through the simultaneous increase in temperature. Increased night-time temperature has a negative effect on rice grain yield.
After analyzing data from Los Banos, Peng et al. (2004) found that the associated grain yield declined by 10% for each 1 °C increase in minimum temperature in the dry season, while there was no clear effect of an increase in maximum temperature.
The latest edition of the Intergovernmental Panel on Climate Change’s report on climate change (IPCC 2007) predicts increased droughts for the African continent. Since most of the African agriculture is rainfed, this will have negative consequences on crop yields.
The same holds for rice production. An estimated 80% of the rice-growing area in Africa is devoted to rainfed rice production, while 48% is for upland and 32% for rainfed lowland production. While rainfed upland rice production will be hit hardest, the rainfed lowland production may be negatively affected too.
Although better protected against drought, rainfed lowlands face an increased probability of being confronted with flooding. While rice can easily withstand flooding it can withstand complete submergence only for a short time.
New rice varieties that have been introgressed with the Sub1 gene can stand submergence for three weeks as was reported by IRRI (Wassmann et al. 2009). At AfricaRice, studies are under way on producing rice with less water.
Increased temperature will lead to an increase in evaporation. Increased evaporation may lead to increased salinity and sodicity inland, while in coastal areas sea level rise will increase salinity. As a result, an increase in salt stress associated with climate chance is expected to occur.
Rice is moderately tolerant to low levels of salt, while mangrove rice varieties are known to withstand high levels of salt. Efforts are being made to identify the genes that confer salt tolerance.
AfricaRice currently has two research projects studying the effect of climate change on pest and diseases. One is studying the effect of climate change on the virulence and distribution of blast and bacterial leaf blight, while the second is concentrating on the effect of climate change on the vigor and distribution of parasitic rice weeds.
Socioeconomic vulnerability to climate change
Africa is one of the less-researched continents in terms of the potential consequences of global warming. Trends suggest that the variability of rainfall will increase and the monsoon regions may become drier, leading to increases in drought-prone areas in the Sahel and southern Africa.
Equatorial zones of Africa may receive more intense rainfall. The overall spatial distribution of future rainfall remains uncertain, however, particularly for the Sahel for which there are a number of contrasting projections.
Climate change is expected to lead to major changes in rainfall distribution, increased frequency of extreme weather events, and generally rising temperatures and CO2 levels. Farmers have great experience in dealing with climate risk, but the fast pace of change means that their local knowledge and technologies may not be sufficient as new conditions emerge.
We need to anticipate such changes and provide alternatives or measures for farmers to adapt to lower and erratic rainfall, higher demand for water, changing river discharges, and so on.
New climate-resilient varieties and crop-and resource-management technologies and institutional innovations such as insurance against crop failure may help them adapt to these rapidly changing environments. Mitigation opportunities are also important.
The impact of the predicted enhanced use of Africa’s lowlands for rice, slash-and-burn practices in upland environments, and increased use of nitrogen fertilizer needs more study to develop as much as possible ways to limit additional release of greenhouse gases into the atmosphere.
In short, a global effort to develop targeted technological options to help African farmers to adapt to and mitigate the effects of climate change is needed.
Sub-Saharan Africa represents one of the poorest regions of the world with a high number of people living below the poverty line. It will be very difficult for these people to protect themselves against climate change, because they do not have the means or the knowledge to deal with the threats that climate change is posing to them. For this reason AfricaRice is involved in research projects that deal with all the threats listed above.
Africa Rice Center (AfricaRice). 2011. Boosting Africa’s Rice Sector: A Research for Development Strategy 2011–2020. Cotonou, Benin: Africa Rice Center.
IPCC 2007. Climate Change 2007: Impacts, Adaptation and Vulnerability. Intergovernmental Panel on Climate Change (IPCC). Online at http://www.ipcc.cg.
Peng SB, Huang, JL, Sheehy JE, Laza RC, Visperas RM, Zhong XH, Centeno GS, Khush GS, Cassman KG. 2004. Rice yields decline with higher night temperature from global warming. Proceedings of the National Academy of Sciences 101: 9971–9975.
Wassmann R, Jagadish SVK, Heuer S, Ismail A, Redona E, Serraj R, Singh RK, Howell G, Pathak H, Sumfleth K. 2009. Climate change affecting rice production: The physiological and agronomic basis for possible adaptation strategies. Advances in Agronomy 101: 59- 122.
Kiepe P, 2012. Rice in Africa. Impacts of climate change on the agricultural and aquatic systems and natural resources within the CGIAR’s mandate (Thornton P, Cramer L, eds), CCAFS Working Paper 23: 131-135.
CCAFS is a strategic partnership of the CGIAR and the Earth System Science Partnership (ESSP). CGIAR is a global research partnership for a food secure future. The program is supported by the Canadian International Development Agency (CIDA), the Danish International Development Agency (DANIDA), the European Union (EU), and the CGIAR Fund, with technical support from the International Fund for Agricultural Development (IFAD).