Longer, hotter, more regular heat waves could impact crop production in Africa, warn climate scientists in a study published in the journal Environmental Research Letters.

Located between the Tropic of Cancer and the Tropic of Capricorn, Africa experiences high levels of solar radiation all year round and heat waves can occur in any season, not just during summer months. Running climate models through to 2075, the scientists found that heat waves could occur as frequently as four times per year towards the end of the century. In other words, one dangerously hot spell for every season of the year. 

The authors examined temperature data from 1979 to 2015 and note that heat waves are unusual but believe they could become a normal occurrence within 20 years.  To make their estimate, the team uses a metric dubbed the Heat Wave Magnitude Index daily (HWMId). The data format takes into account the severity of the temperature extremes as well as the number of consecutive days of hot weather. Using this approach, the group can compare heat waves occurring in different places and at different times of the year, but there are other details to factor in.

"The severity of the impact on human mortality and crop production depends on the vulnerability of the communities affected and the environmental systems," said Jana Sillmann of the Center for International Climate and Environmental Research (CICERO), one of the institutions taking part in the study. "For example, the heat wave in Finland during 1972--which we have studied previously--was comparable to the period of hot weather occurring in Central Europe during 2003. However, the latter event was responsible for more deaths than the Finnish heat wave."