doi:10.1038/nindia.2015.2 Published online 13 January 2015
Putting together results from 30 different crop models, scientists from across the world estimate that for every degree rise in temperature, the global wheat production is expected to go down by 6 per cent1. South Asia, including India, is projected to be amongst the worst hit in terms of wheat production as temperatures soar.
A consortium of scientists, which tested crop models in wheat fields with mean growing season temperatures between 15ºC to 32ºC, suggests that more temperature resilient varieties of wheat and early warning systems could help meet challenges that climate change is bound to pose to food security.
“Normally, we use one model to see temperature impacts. This study took into account 30 different models and extrapolated the ensemble temperature response,” says Pramod Aggarwal, one of the authors from India in the multinational study. Aggarwal, the south Asia head of International Water Management Institute’s programme on Climate Change, Agriculture and Food Security (CCAFS) says the impact of warming on south Asia’s wheat yields is expected to be highest. The losses are expected to be higher than previously thought.2
The scientists estimate that the world will lose 42 Mt of wheat with each degree rise of temperature considering the present global production rate of 701 Mt in 2012. This, the study points out, is a quarter of global wheat trade, pegged at 147 Mt in 2013.
The most notable take home of the study is that change in temperature requires an adaptation strategy different from one that looks at change in rainfall. According to the authors, locations where plants suffer from high temperature stress have been identified across the globe. But none of the crop models have been tested systematically against experiments at different temperatures in field conditions. Glasshouse or controlled-environment temperature experiments are not suitable for model testing since heating of root systems in pots and effects on micro-climate are vastly different from field conditions.
The global study got underway after detailed information on field experiments on a wide range of sowing dates and infra red heating became available for wheat recently. The scientists chose the experimental locations using country statistics and disaggregated global mean surface temperature increases to regional surface temperature changes.
The modellers carried out simulations in a ‘blind' test with phenology and yield data at normal temperature. Higher temperatures meant the number of days during which plants could intercept light for photosynthesis went down and this resulted in reductions in biomass and grain yields.
The scientists found that wheat grains failed to set when the mean temperature was greater than 28ºC and when there were extremely high temperatures early in the growing season.
“Since warming is a reality we are faced with, it would be imperative to continuously monitor agriculture systems and come up with early warning systems that can project crop production in short term,” Aggarwal says. The impact of soaring temperatures on wheat yields can be compensated by altering sowing dates, using different cultivars and effective fertilisers, he says.
For rice yields, an increase in temperature would not be as significant since paddy is less sensitive to temperature. However, indirect effects on production such as floods, cyclones and food storage losses are not accounted for in such studies and would be worth taking note as well, Aggarwal says.