Detailed modelling by climate, agronomic and environmental scientists from Europe and the US lead them to conclude that heat-induced water stress is likely to lead to catastrophic impacts on yields of major food crops such as wheat, maize and soybeans.
In a paper entitled “Consistent negative response of US crops to high temperatures in observations and crop models”, published on 19 January in the journal Nature Communications, the scientists say that the increasing frequency of prolonged growing season periods during which daytime temperatures reach between 30°C and 36°C could lead to future yield losses of as much as 40% for soybeans, 49% for maize and 22% for wheat between now and the end of the century.
The scientists modelled wide areas of the US where these three crops are produced, bearing in mind that the country is the world’s biggest producer of soybeans and maize, and the second-largest producer of wheat. They found that temperature-induced water stress is the main driver of yield decline at temperatures above 30°C as plants seek more water on hot days and the soil-to-water supply decreases as soil water stocks deplete. The plants then instinctively try to conserve water loss by closing their stomata – through which they take in CO2 into their cells – thus cutting off their engine of photosynthetic growth. And hence the resulting drop in yield.
The findings also confirmed that yields suffer less in irrigated areas, as the degree of water stress is mitigated compared to areas watered only by rain. However, as global warming could increase the incidence of drought periods, it may limit the amount of water available for irrigation schemes, particularly high-volume traditional systems.
Should the yields of major food crops drop by as much as the cited paper suggests, it would have significant economic and humanitarian impacts. The three crops modelled represent 62% of total US arable land. A 49% drop in the US maize yield would (at 2015 values) represent a loss of some USD 29 billion. Globally, food security could reach crisis point. The world’s population by 2050 is estimated to grow to around 9.7 billion, meaning that farms need to produce enough to feed almost 2.4 billion more people than now. Much of the additional population will be in Africa and Asia, the two continents likely to suffer the most from temperature extremes and water stress.
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Published on 29 March 2017