3. 187
Chapter EIGHT
Global warming impact
on rice crop productivity
D.P. Singh
Abstract
Rice is a major food crop of Asia and of the world. The
impact of global warming on rice may be due to a rise in
sea level, thus resulting in inundated lands with sea water
which makes these lands unsuitable for rice cultivation.
Climate change is estimated to affect 20 million hectares
of the world’s rice-growing area adversely, mainly in India
and Bangladesh. It is forecasted by the International Food
Policy Research Institute that by 2050, the rice prices
will increase between 32% and 37% as a result of climate
change due to the reduction in rice productivity by 14% in
South Asia, 10% in East Asia and the Pacific and 15%
in sub-Saharan Africa. The rise in carbon dioxide levels
in the environment may result in higher biomass in rice,
which, depending on the type of cultivars, may or may not
Contents
Abstract 187
8.1 Introduction 188
8.2 Global warming 188
8.3 Global warming and rice productivity 189
8.4 Land and water resources for rice 191
8.5 Salinity, flooding and rice 193
8.6 Water shortage and rice productivity 194
8.7 Global warming and its impact on pests, diseases
and weeds 194
8.8 Strategies for mitigating effects of global
warming on rice production 195
References 196
4. 188 Climate Change Effect on Crop Productivity
increase the grain yield. Climate change may be tackled
by adopting proper strategies in research and policies of
different countries. A proactive approach to this may save
the rice production, as well as help in reducing emissions
of greenhouse gas ‘methane’ from rice cultivation.
8.1 Introduction
The world population is growing steadily on the one hand,
whereas land and water resources are declining on the other.
Rice is the primary staple food for more than half the world’s
population. Asia represents the largest producing and consum-
ing region. A total of 651 million tonnes of rice (paddy) was
harvested in Asia in 2012 (FAOSTAT, 2012). Rice production is
rising in SouthAsia but falling in the east. It is also a staple food
in sub-Saharan Africa, preferred in China and the only available
domestic staple in many countries in Asia (FAOSTAT, 2010).
An increase in rice production by ≈1% annually is estimated to
meet the growing demand for food that will result from popu-
lation growth and economic development (Rosegrant et al.,
1995). Global population is predicted to rise to over 9 billion
by 2050, which will lead to a 25% increase in the demand for
rice. Most of this increase must come from greater yields on
existing cropland to avoid environmental degradation, destruc-
tion of natural ecosystems and loss of biodiversity (Cassman,
1999; Tilman et al., 2002). During this period, a warmer climate
may decrease rice yields by 8%. Fresh global water supply will
be needed to accommodate increased rice production and an
additional 57,280,000,000 L (1432 L × 40,000,000 kg) of fresh
water will be required. Fresh water demands will be more in
highly populated countries like India and China, which are the
main producers of rice in the world.
8.2 Global warming
‘Global warming’ refers to the rise in the average temperature
of the earth’s atmosphere and oceans. The greenhouse gases
(carbon dioxide, water vapour, nitrous oxide and methane) trap
heat and light from the sun in the Earth’s atmosphere and lead
to an increase in the temperature. Huge quantities of green-
house gases are released into the atmosphere due to mining and
combustion of fossil fuels, deforestation and maintenance of
livestock herds and also due to rice production. The increase in
5. 189Global warming impact on rice crop productivity
temperature harms people, animals and plants, including rice.
The higher the concentration of greenhouse gases, the more the
trapping of heat in the atmosphere and the reduced escape of
heat back into space. The higher heat results in a change in cli-
mate and altered weather patterns. In 2001, the ‘UN-sponsored
Intergovernmental Panel on Climate Change’ reported that
worldwide temperatures have increased by more than 0.6°C in
the past century and estimated that by 2100, average tempera-
tures will increase by between 1.4°C and 5.8°C (Nguyen, 2005).
8.3 Global warming and rice productivity
High temperatures or global warming would decrease the rice
production globally (Furuya and Koyama, 2005). There is a
need to plan for appropriate strategies to adapt to and miti-
gate the global warming for achieving long-term food secu-
rity. Both lowland rice cultivation and upland rice production
under slash-and-burn shifting cultivation results in the emis-
sion of methane and nitrous oxide gases and, thus, contributes
to global warming. Increased concentration of carbon dioxide
in the atmosphere along with rising temperatures are two major
factors making rice agriculture a larger source of greenhouse
gas ‘methane’ which may double by the end of this century.
Methane is produced from carbon and hydrogen by bacteria
in the soil. Some carbon enters the soil from the roots of rice
plants, which have taken it from the atmosphere via photosyn-
thesis. The rice plants grow faster under higher carbon dioxide
concentration. This growth, in turn, pumps up the metabolism
of methane-producing microorganisms in soil in rice field,
thus generating more methane. Rice farming is responsible for
approximately 10% of the methane released. Researchers at
Northern Arizona University gathered published research from
63 different experiments on rice paddies, mostly from Asia and
North America. The meta-analysis was used and found two
strong patterns: first, more carbon dioxide boosted emissions
of methane from rice paddies, and second, higher temperatures
caused a decline in rice yields. According to the study, in the
future the amount of methane emitted from rice paddies is
likely to increase. Together, higher carbon dioxide concentra-
tions and warmer temperatures predicted by the end of this cen-
tury will double the amount of methane emitted per kilogram
of rice produced (NAU, 2013). Since half of the worlds’ human
population is highly dependent on rice, the production systems
for this crop are, thus, vital for the reduction of hunger and
6. 190 Climate Change Effect on Crop Productivity
poverty. The cultivation of rice extends from dry lands to wet-
lands and from the banks of the Amur River at 53° north latitude
to Central Argentina at 40° south latitude. Rice is also grown
in cool climates at altitudes of over 2600 m above sea level in
the mountains of Nepal, as well as in the hot deserts of Egypt.
However, most of the annual rice production comes from tropi-
cal climate areas. In 2004, more than 75% of the global rice
harvested area (about 114 million out of 153 million ha) came
from the tropical region whose boundaries are formed by the
Tropic of Cancer in the Northern Hemisphere and the Tropic
of Capricorn in the Southern Hemisphere (Nguyen, 2005). The
temperature increases, which results in rising seas and changes
in rainfall patterns and distribution, and may affect the land and
water resources required for rice production and achieving the
desired productivity of rice crops. The highest limit of tempera-
ture for growth of rice is 45°C and temperatures above this will
be adverse for yields. The optimum temperature range for rice
at different stages after germination is 35–31°C whereas for rip-
ening it is 20–29°C (Table 8.1). The temperature may affect and
produce abnormal symptoms in rice (Table 8.2). Such a rapid
increase during the crop growth stages, particularly during
extremely sensitive reproductive and early grain-filling stages
of rice (Oryza sativa L.), leads to reduced biomass, grain yield
and quality. Hence, increasing diurnal temperature tolerance in
Table 8.1 Critical temperatures for the development of rice
plant at different growth stages
Growth stages
Critical temperature (°C)
Low High Optimum
Germination 16–19 45 18–40
Seedling emergence 12 35 25–30
Rooting 16 35 25–28
Leaf elongation 7–12 45 31
Tillering 9–16 33 25–31
Initiation of panicle primordia 15 − −
Panicle differentiation 15–20 30 −
Anthesis 22 35–36 30–33
Ripening 12–18 30 20–29
Source: From Yoshida, S. 1978. Tropical Climate and Its Influence on
Rice. IRRI Research Paper Series 20. Los Baños, Philippines,
IRRI.
7. 191Global warming impact on rice crop productivity
rice is a more sustainable approach than altering well-estab-
lished cropping patterns, which will inevitably lead to yield
penalties (Nagarajan et al., 2010). The current temperatures are
already approaching critical levels during the susceptible stages
of the rice plant, namely, Pakistan/North India (October), South
India (April, August), East India/Bangladesh (March–June),
Myanmar/Thailand/Laos/Cambodia (March–June), Vietnam
(April/August), Philippines (April/June), Indonesia (August)
and China (July/August) (Wassmann et al., 2009b).
8.4 Land and water resources for rice
The increase in temperature will create more land and water
for growing rice in areas outside the tropical region (Darwin
et al., 2005). The areas of coastal regions in the United States
(Florida, much of Louisiana), the Nile Delta and Bangladesh
will become unsuitable for rice with the rise of sea level by
88 cm (Kluger and Lemonick, 2001).
During the last two decades, night temperatures have
increased at a much faster rate than day temperatures and global
climate models predict a further increase in its frequency and
intensity. The rice crop is affected both at the vegetative and
reproductive stage due to a rise in temperature and, hence, pro-
ductivity is also affected. The temperatures required at different
crop growth phases are given in Table 8.1. High temperatures
may result in various possible injuries to rice crops (Table 8.2).
High temperatures for 1–2 h at anthesis may result in sterility
of the rice crop. Mohandrass et al. (1995) predicted a decline
in yield by 14.5% in summer rice in India by 2005 based on
experiments at multi-locations. In the Philippines too, yields
of dry-season rice declined by 10% for every 1°C increase in
growing-season minimum temperatures, whereas the effect of
Table 8.2 Symptoms of heat stress in rice
Growth stage Symptoms
Vegetative White leaf tip, chlorotic bands and
blotches, white bands and specks, reduced
tillering, reduced height
Reproductive anthesis Reduce spikelet number, sterility
Ripening Reduced grain-filling
Source: From Yoshida, S. 1981. Fundamentals of Rice Crop Science.
Los Baños, Philippines, IRRI. 269 pp.
8. 192 Climate Change Effect on Crop Productivity
maximum temperature on crop yields was insignificant. Peng
et al. (2004) provided evidence in support of statements that
decreased rice yields from increased nighttime temperature was
associated with global warming. Temperature and radiation had
statistically significant impacts during both the vegetative and
ripening phases of the rice plant. Welch et al. (2010) concluded
that diurnal temperature variation must be considered when
investigating the impacts of climate change on irrigated rice
in Asia. Higher temperatures can adversely affect rice yields
through two principal pathways, namely (i) high maximum
temperatures that cause—in combination with high humid-
ity—spikelet sterility and adversely affect grain quality, and (ii)
increased nighttime temperatures that may reduce assimilate
accumulation. On the other hand, some rice cultivars are grown
in extremely hot environments, so that the development of rice
germplasm with improved heat resistance can capture an enor-
mous genetic pool for this trait. The results show that high night
temperature compared with high day temperature reduced the
final grain weight by a reduction in grain growth rate in the
early or middle stages of grain filling, and also reduced cell size
midway between the central point and the surface of the endo-
sperm (Morita et al., 2005). In the Philippines, rice production
may decline up to 75% by 2100 because of global warming
and Filipinos will have to settle for meals with little or no rice
unless the government aggressively implements climate change
adaptation programmes (Antiporda, 2013). Transpiration from
rice panicles can help lower the temperature of the panicle,
which is the susceptive organ for high-temperature-induced
spikelet sterility. By increasing the transpiration, the heat dam-
age to the panicle predicted to occur due to global warming
may be avoided. To examine the possibility of genetic improve-
ment in transpiration conductance of intact rice panicles (gpI),
we measured gpI at the time of flowering in the open field in
21 rice varieties of widely different origins. Thus, the target of
improvement in gpI against high-temperature-induced spikelet
sterility should be set at the level of the existing varieties with
the highest gpI (Fukuoka et al., 2012). Tao et al. (2008) stud-
ied the impact of global warming on rice production and water
use in China, against a global mean temperature. They found
the median values of rice yield decrease ranged from 6.1% to
18.6%, 13.5% to 31.9% and 23.6% to 40.2% for GMT changes of
1°C, 2°C and 3°C, respectively. Yoshimoto et al. (2010) synthe-
sised a process-based model study in tandem with FACE exper-
iments for studing the effects of climate change on rice yields
in Japan. They found that it not only contributes to reducing
9. 193Global warming impact on rice crop productivity
the evaluation uncertainties, but also validates the adapting
or avoiding studies of heat stress or negative influence on rice
under projected climate change. The biomass production in rice
will be more, which may or may not increase the grain yield.
The higher temperatures can result in sterility in flowers, which
will then adversely affect yields. The higher respiration losses
due to a rise in temperature will also make rice less productive.
IRRI research indicated that a rise in nighttime temperature by
1°C may result in losses in rice yields by about 10%.
8.5 Salinity, flooding and rice
Rice is highly sensitive to salinity. Salinity often coincides
with other stresses in rice production, namely drought in inland
areas or submergence in coastal areas. Submergent tolerance
of rice plants has substantially been improved by introgressing
the Sub1 gene into popular rice cultivars in many rice-growing
areas in Asia. The rice crop has many unique features in terms
of susceptibility and adaptation to climate change impacts due
to its semi-aquatic phylogenetic origin. The bulk of global rice
supply originates from irrigated systems, which are to some
extent shielded from immediate drought effects. The buffer
effect of irrigation against climate change impacts, however,
will depend on the nature and state of the respective irrigation
system (Wassmann et al., 2009b). Although rice can grow in
water fields, submerged crops under water for long periods of
time are not tolerated by rice plants. Flooding due to sea level
rises in coastal areas and tropical storms will hinder rice pro-
duction. At present, about 20 million hectares of the world’s
rice-growing area is at risk of occasionally being flooded to
submergence level in India and Bangladesh. Wassmann et al.
(2009b) in his review paper mentioned that the mega-deltas in
Vietnam, Myanmar and Bangladesh are the backbone of the
rice economy in the respective country and will experience
specific climate change impacts due to sea level rise. Significant
improvements of the rice production systems, that is, higher
resilience to flooding and salinity, are crucial for maintaining
or even increasing yield levels in these very productive del-
taic regions. The other ‘hotspot’ with especially high climate
change risks in Asia is the Indo-Gangetic Plains (IGP), which
will be affected by the melting of the Himalayan glaciers.
The dominant land use type in the IGP is rice–wheat rotation.
The geo-spatial vulnerability assessments may become cru-
cial for planning targeted adaptation programmes, but policy
10. 194 Climate Change Effect on Crop Productivity
frameworks are needed for their implementation (Wassmann
et al., 2009a).
8.6 Water shortage and rice productivity
Rice cultivation needs plenty of water. The changes in climate
leading to a week without rain in upland rice-growing areas
and 2 weeks in shallow lowland rice-growing areas can cause
reduction in rice yields in the range of 17–40%. The intensity
and frequency of droughts are predicted to increase in rain-fed
rice-growing areas. Such changes are also expected in reduce
water-short irrigated areas for rice cultivation. It affects rain-
fed rice production in an area of 23 million hectares in South
and Southeast Asia and about 20 million hectares of rain-fed
lowland rice in Africa. The scarcity of water may also affect
rice production in Australia, China, the United States and other
countries. Drought stress is also expected to aggravate through
climate change; a map superimposing the distribution of rain-
fed rice and precipitation anomalies in Asia highlights espe-
cially vulnerable areas in East India/Bangladesh and Myanmar/
Thailand (Wassmann et al., 2009a,b).
8.7 Global warming and its impact on pests,
diseases and weeds
The IRRI experiments over the last 10 years at farmers’ fields
indicated that rice diseases and pests are influenced greatly by
climate change. The incidence of diseases like brown spot and
blast increases due to shortages of water, irregular rainfall pat-
terns and related water stresses. On the other hand, the inci-
dence of sheath blight or whorl maggots or cutworms reduces
due to a change in the environmental conditions and shifts in
production practices adopted by farmers to reduce the impact
of climate change. It, thus, results in an emergence of new crop
health dynamics. Global warming will enhance rice–weed com-
petition. Rodent population outbreaks in Asia may increase due
to unseasonal and asynchronous cropping as a result of extreme
weather events. A combined simulation model (CERES-Rice
coupled with BLASTSIM) was used to study the effects of
global temperature change on rice leaf blast epidemics in sev-
eral agro-ecological zones in Asia. At least 5 years of historical
daily weather data were collected from each of 53 locations
in five Asian countries (Japan, Korea, China, Thailand and
11. 195Global warming impact on rice crop productivity
Philippines). Two weather generators, WGEN and WMAK,
from the Decision Support System for Agrotechnology Transfer,
were utilised to produce estimated daily weather data for each
location. Thirty years of daily weather data produced by one of
the generators for each location were used as input to the com-
bined model to simulate blast epidemics for each temperature
change. Maximum blast severity and the area under the disease
progress curve caused by leaf blast which resulted from 30-year
simulations were statistically analysed for each temperature
change and for each location. Simulations suggest that tempera-
ture changes had significant effects on disease development at
most locations. However, the effect varied in different agro-eco-
logical zones. In the cool subtropics such as Japan and north-
ern China, elevation of temperature above normal temperature
resulted in more severe blast epidemics. In warm/cool humid
subtropics, elevation of temperature caused significantly less
blast epidemics. However, lower temperature caused insignifi-
cant difference in disease epidemics compared with that in nor-
mal temperature. Conditions in the humid tropics were opposite
to those in cool areas, where daily temperature changes by −1°C
and −3°C resulted in significantly more severe blast epidemics,
and temperature changes by +1°C and +3°C caused less severe
blast. Scenarios showing blast intensity affected by temperature
change in different agro-ecological zones were generated with a
geographic information system (GIS) (Luo et al., 1998).
8.8 Strategies for mitigating effects of global
warming on rice production
The paddy experiments carried out at UC Davis and Trinity
College Dublin indicated that increased carbon dioxide in the
atmosphere boosted rice yields by 24.5% and methane emis-
sions by 42.2%, increasing the amount of methane emitted per
kilo of rice (Soos, 2012). There are several options available to
reduce methane emissions from rice agriculture. The manage-
ment practices such as mid-season drainage and using alterna-
tive fertilisers as well as switching to more heat-tolerant rice
varieties and adjusting sowing dates are some of the measures
suggested to reduce the methane emissions (NAU, 2013).
The following are few of the strategies which may be adopted
to counter the effect of global warming on rice:
1. To breed and release new rice cultivars with better adap-
tation to high temperature and other climatic stresses
12. 196 Climate Change Effect on Crop Productivity
2. Develop new agro-ecosystem models which may be
capable of predicting more correctly the consequences of
climate change and land use change at different scales
3. Deployment of new management strategies for an eco-
logical intensification of rice landscapes in Asia for
increasing resource use efficiency, enhanced ecosystem
resilience and a reduction in global warming potential
4. Create national and regional adaptation and mitigation
policies for climate change on rice-based agriculture and
net contributions of rice systems to global warming
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