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.
References
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.
Source
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).
