Night warming threatens rice output in Asia

Hotter nights arising from climate change will put a brake on the rise in rice production in Asia over the coming decades, with the effect worsening as the century progresses, scientists said yesterday (9 August).

The first study to use ‘real-world’ data from farmer-managed rice farms has shown that, while hotter days may boost productivity, hotter nights more than compensate by reducing it.

"There is very little doubt that higher night temperature is harmful to rice and that further increases will continue to harm production unless there are technological changes in the way is produced," lead author of the study Jarrod Welch, from the University of California in San Diego, told SciDev.Net.  

The researchers analysed six years of data collected by the International Rice Research Institute (IRRI) in the Philippines from nearly 230 farmer-managed irrigated farms across six major rice-growing countries in Asia.  

The international team wanted to disentangle the effects on rice productivity of three factors: daytime temperature, night temperature and sunshine.

The scientists confirmed what previous, experimental trials have suggested: that warmer temperatures lead to a net decline in production.

The reason for the fall in productivity at night may lie in a key stage in the rice plant’s cycle: grain filling. It is thought that, at night, energy needed for grain-filling goes instead to power the increased respiration a plant requires in hotter weather.

The scientists’ long-term prognosis is even worse because, once day time temperatures reach a certain height they, too, will start to restrict the rice growth cycle, leading to an additional loss in production.

The phenomenon is set against a background of increased rice productivity, achieved through improvements in technology such as better seeds, use of fertiliser and mechanisation. The net effect will be a slowing down of the rate of growth of rice yield.

Reiner Wassmann, coordinator of the Rice and Climate Change Consortium at IRRI, said that plant-breeding using rice varieties that have evolved traits to adapt to very hot environments could provide a way forward.

Hilton Pinto, director of the Center for Meteorology and Climate Research Applied to Agriculture at the Brazilian university Unicamp, told SciDev.Net  that adaptation of agriculture to climate has to begin immediately.

"If we want to obtain a new variety of plant more resistant to high temperatures we need to start now. This takes ten years of work with an estimated cost of one million dollars per year in research. Let’s start now."

In Asia, where 60 per cent of the world’s population lives, each hectare of land used for rice provides food for 27 people. By 2050, IRRI estimates the same land will have to feed 43 people.

Link to paper abstract in Proceedings of the National Academy of Sciences