Vapour pressure deficit determines critical thresholds for global coffee production under climate change

This study examines Arabica coffee production responses to key seasonal climate drivers, namely, temperature, precipitation, soil moisture and vapour pressure deficit, in 13 of the world's most important producing countries. Through threshold regression and generalized additive models, threshold responses are identified that could translate into rapid coffee yield declines under climate change. Our understanding of the impact of climate change on global coffee production is largely based on studies focusing on temperature and precipitation, but other climate indicators could trigger critical threshold changes in productivity. Here, using generalized additive models and threshold regression, we investigate temperature, precipitation, soil moisture and vapour pressure deficit (VPD) effects on global Arabica coffee productivity. We show that VPD during fruit development is a key indicator of global coffee productivity, with yield declining rapidly above 0.82 kPa. The risk of exceeding this threshold rises sharply for most countries we assess, if global warming exceeds 2 degrees C. At 2.9 degrees C, countries making up 90% of global supply are more likely than not to exceed the VPD threshold. The inclusion of VPD and the identification of thresholds appear critical for understanding climate change impacts on coffee and for the design of adaptation strategies.