African maize yields will fall under increasing temperatures

To those following the scientific research on climate impacts on agriculture in Africa, the theme of this post should come as no surprise. Stanford research David Lobell and colleagues merely add to work that has already been published by that research group. Their latest study adds much more empirical data analysis to much modeling already undertaken, with confirmation of the grim scenarios foreseen for agriculture on the African continent.

Using data from maize/corn variety trials carried out over more than ten years across Africa they provide further evidence of the effects of temperature on maize production. In particular, the number of degree days that exceed 30 degrees C has significant effect -- "each degree day spent above 30 degrees C reduced final yield by 1% under optimal rain-fed conditions, and by 1.7% under drought conditions."

High temperatures affect the moisture status of the soil, thereby increasing stress on the plant. As well, high temperatures were especially problematic during silking and pre-silking stages.

Their work concludes with analysis of the cumulative impact of degree days above 30 degrees C -- linking the impacts of daily temperature maximums seen during a season with what would be expected over the next decades with each 1 degree C of warming seen.

For sites with average temperatures above 25 degrees C yields decline rapidly with increasing temperatures, "because of frequent exposure to temperatures above 30 degrees C, with more than 10% yield loss per degree C of warming... Under drought conditions, even the coolest trials are harmed by 1 degree C warming, with losses exceeding 40% at the hottest sites."

The graphs and maps included in the paper are sobering.