International researchers have more precisely measured how extreme weather events driven by a changing climate can devastate crop yields.

Hot and cold temperature extremes, drought and heavy precipitation account for 18 to 43 percent of variations in global yields for maize, spring wheat, rice and soybeans.

“Climate extremes such as heat waves or droughts can have devastating effects on agricultural yields,” said lead author Elizabeth Vogel with the Centre of Excellence for Climate Extremes and Climate and Energy College at the University of Melbourne in Australia.

“For example, the millennium drought in Australia from 1997 to 2009 was among the worst droughts in the last several centuries and had severe impacts on agriculture. In southeast Australia, rice production went down by 99 percent between 2002 and 2009 and wheat yields dropped by 12 per cent during the drought.”

The European heat wave and drought in summer 2018 led to widespread harvest failures and shortages of livestock feed.

Similar drought conditions last year challenged farmers and ranchers in Western Canada as hay and livestock feed dwindled.

Driving the fears of global drought is that climate change is triggering more intense variable climate events and also increasing the frequency and severity of climate extremes.

Researchers from Australia, Germany and the United States were involved in the project.

The research team investigated the effects of year-to-year climate variability and extremes on yields of four crops — corn, rice, soybeans and wheat to better understand climate impacts. While they expected climate factors would obviously influence crop yields, they were particularly interested in how these fluctuations were explained specifically by climate extremes. They used a global agricultural database algorithm called Random Forests to show which climate factors played the biggest role in influencing crop yields.

Vogel said a Random Forest algorithm can identify patterns in large datasets and create predictive, statistical models.

Our results showed that 18 percent to 43 percent of the variance in yields is accounted for by climate extremes. For maize, soybeans and rice, this represents more than half of the explained variance.”

They found the most important climate factors for fluctuations in crop yield were related to temperature, not precipitation. Vogel wrote that temperature-related predictors were more strongly correlated with variable crop yields than precipitation-related predictors across all four crops.

The team also identified global hot spots of particular importance for global production yet highly susceptible to the influence of climate, and especially climate extremes, during the growing season.

“As industrialized agricultural regions contribute a large share of world production, many of these regions were among the hot spots … North America, Europe and Oceania still make up most of the hot spots.”

In the study, maize yields in Africa showed one of the strongest relationships with the climate variabilities in the growing season.

“Our results show a particularly strong relationship between climate variations and year-to-year fluctuations in maize yields. These results agree with other previous studies that have shown a strong link between climate variability and extremes, particularly heat extremes, and maize yields. We also see strong effects on spring wheat yields at the global scale and some influences on rice and soybean yields in many regions.”

She said there was no clear answer why the signal was particularly strong for maize, but she suggested that crop-specific temperature and water stress sensitivities, varying management practices and differences in growing seasons between the different crops may play a role.

Production of maize in Africa is particularly critical since a large percentage of the crop is for human consumption, making it an essential source of food security in the region.

“Communities that highly depend on subsistence farming are particularly affected by the effects of climate extremes on crop production,” said Vogel. She said African maize showed one of the strongest associations between climate variations during the growing season and yield anomalies of all the crop-continent combinations. Climate factors explained about 55 percent of maize yield variations in the region.

“Our study highlights the need to adapt food production to climate extremes, not only in major crop producing countries, but also in regions with a strong dependence on subsistence farming or a high share of production for human consumption.”

Some mitigation approaches include shifting the growing season if possible, development of drought or heat-tolerant crop varieties, irrigation, water conservation, and accurate seasonal weather forecasting.