Rice yields will fall this year.
That’s the dire projection made by the Climate Change in Southeast Asia Program, Yusof Ishak Institute, Singapore.
The heat wave from March to May saw temperatures rise above 45 degrees Celsius in Thailand, Myanmar, and Laos, and above 40° C in Cambodia, Vietnam, and Malaysia. It delayed the rice planting season.
It will impact on the Philippines, the second-largest importer of rice after China. In July, Typhoon Egay wiped out 22 percent of the country’s annual production, according to an Associated Press report.
“Rice production, like most of agriculture, is highly dependent on favorable climate,” said Elyssa Ludher and Paul Teng in a briefing paper for the Yusof Ishak Institute.
El Niño is expected to prolong the warm, dry weather in mid-2023 into mid-2024, causing plants to experience heat stress, which impacts growth and ultimately, yield.
Heat stress causes water loss, delayed growth, reduced pollination, impaired seedling or root growth, withered or yellow leaves, reduced number of tiller, the grain bearing branch, and seedling death in plants.
Generally, temperatures above 33° C have commonly resulted in rice yield reductions. One study by the International Rice Research Institute (IRRI) in the Philippines has found that for every 1° C increase in average night-time temperatures during the dry season, there is a corresponding 10 percent yield loss on average.
The optimum temperature for rice at seedling stage is 25° C to 28° C and for germination at 28° C to 30° C.
Temperatures above that reduces yield — for example, by increasing sterility, delaying flowering, and shortening fertilization periods.
Heat stress at later, grain filling stages reduces starch accumulation and may increase chalkiness in grains, resulting in reduced translucence of rice and milling quality. Lower grade rice means lower commercial values — resulting in economic losses for farmers.
With El Niño likely bringing record-breaking temperatures, yields are expected to be reduced, said Ludher and Teng.
Both experts said research to develop climate-resilient varieties is important as the heat stress effects on rice yields are dependent on the timing (when it happens), severity (how high the temperature and humidity levels are) and duration (how long it lasts) of the heating event during the growth and developmental stages of the crop.
Any genetic improvement in rice varieties needs to address all stages of the plant’s development.
Rice responds to heat stress in different settings. As compared to Japonica rice, Indica rice is more heat-tolerant and suitable for high-temperature environments.
Indica rice is the dominant rice grown in Southeast Asia (Jasmine, Phka Rumduol and other fragrant and non-fragrant varieties). Japonica rice (short grain) is mostly grown in the highlands of the region, though a tropical derivative — the Javanica — is popular in Indonesia.
Abnormally warm temperatures in the highlands can thus have a greater impact on rice yields than on yields in lowlands.
“Heat stress can be alleviated with irrigation,” said Ludher and Teng.
“However, as El Niño results in reduced precipitation, there is little reprieve for rice farms dependent on rains. Irrigated farms also face competing pressures on the water use of residential, industrial or biodiversity needs.”
