Dr Zuhair Hasnain
MASSIVE research and evidence have shown that
climate is changing rapidly and overall influence
of this change is negative on rice productivity. Asia is vitally important continent which comprises majority of rice producing countries extending from Pakistan to Japan. 17 out of 25 major rice producing nations are present in Asia which collectively produces 92% of rice and consumes 90% of the world’s total rice production. Climate change alters both the area of rice production and its yield per unit area. The extent of area in which rice is grown is affected by changes in environmental factors which, in result, decide whether rice crop will grow or not, also reduces yield below a threshold level. Climate change directly affects the physiological mechanisms of rice such as photosynthesis which influences the yield per unit area. In Asia, rice is grown in coastal areas and low lying deltas where rise in sea level will make rice vulnerable to grow. More than half of rice produced in Vietnam is affected by rise in sea level. Rise in sea level results in flooding which hinders the rice production especially in countries such as Bangladesh and India. Increased intensity of storms in conjunction with climate change also declines crop productivity.
Another fallout of rising sea levels is soil salinity. As rice is moderately tolerant to saline soils, so yield is also reduced as a result of raised sea level induced salinity. Increased carbon dioxide concentration tends to increase crop growth and yield because of its influence on photosynthetic rate of crop plants. On the other hand, temperature rise decreases crop yield as it urges crop plants to mature early than normal period, so crop has not enough time to give bumper yield. Higher temperature results in higher respiration losses which makes the rice less productive. Both variables ie carbon dioxide and temperature determines the productivity of rice in a given region. According to the International Rice Research Institute (IRRI) 1 degree Celsius rise in night temperature may result in 10% decline in rice yield. As climate is changing, so the intensity and frequency of drought are increasing in rainfed rice growing areas. Shortage of water affects more than 23 million hectares of rainfed area under rice production in South and South East Asia. Moreover, changes in climatic conditions are somehow intensifying the rice pests and diseases such as brown spot and blast disease of rice. Infestation of weed and crop-weed competition are also increasing in rice fields in a result of fluctuating environmental conditions. In India, out of the 42 million ha of total area under rice production, about 45% is irrigated, 33% is rainfed lowland, 15% is rainfed upland, and 7% is flood-prone.
As paramount area comes under rainfed conditions so distribution of rainfall is a critical factor in rice production in this region. It is predicted that rice production will increase in India due to high CO2 and temperature levels and fertilizing impact of increased CO2 concentration is strong enough to mitigate the negative impact of hot temperatures in a region. Malaysia is also self-sufficient in her rice needs to some extent. Rest, it imports from other trading partners. In Malaysia, major problem of low rice production is alteration of people’s preferences in consuming rice as staple food, which in last 20 years, dropped from 100 to 70 kg of rice consumed per capita. This result in shrinkage of area under rice cultivation and other constraints are unpredicted rainfalls, monsoon floods and periodic droughts which are the ultimate results of climate change. Rice being the staple food of South Korea is grown there 3000 years ago. Drought stress at seedling growth and transplanting stage tends to decline crop yield. Flooding damage occurs as a result of heavy rainfall from July to September. High temperature in summer also leads to spikelet sterility. Climate change results in an average loss of about 11% in rice yield. In China, increased carbon dioxide concentration increases crop yield and high temperature results in declined rice production.
Overall, both variables determine the final productivity in a specific region. According to Geophysical Fluid Dynamics Laboratory (GFDL) model scenario, overall production of rice in China is simulated to be changed by +12.2%. Majority of crops faces decline in yield due to high temperatures at flowering stage which results in significant spikelet sterility. In the Philippines, average results of different models indicate a 2.1% loss in rice production. This change is significant in dry seasons. Japan is self-sufficient for its rice grain needs. In this region, almost all of rice is grown in paddy fields. Major climatic factors influencing the rice crop in Japan are strong winds, solar radiations, temperature and heavy rainfall linked with typhoons which is a major cause of decline in yield of crop. Main factor influenced by high temperature in rice crop is spikelet sterility as it is extremely sensitive to temperature below 20°C and above 33°C hence, a small change in this temperature change causes decline in crop yield. Varietal adaptation, such as tolerance to hot temperatures, is a best way to mitigate the adversities of increasing temperatures on rice crop. Genetic modification of rice plant is a dire need of time to combat climate change. As the International Rice Research Institute (IRRI) is trying to develop C4 rice which will have supercharged mechanism of photosynthesis, ability to utilize CO2 in a better way and yield up to 50% more than present varieties. Suitable management strategy should be adopted to cope up with the impacts of climate change. The International Food Policy Research Institute (IFPRI) forecasts increase in price between 32 and 37% and yield loss between 10 and 15% by 2050.
—The writer is Assistant Professor and Project Director Attock Campus, PMAS Arid Agriculture University Rawalpindi.