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High temperature alone would lead to a well-understood loss of crop yields, but the compounding effects by other global change factors are much less well understood and can either amplify or reduce temperature-driven yield change. Analysis focusing on U.S. maize yield shows that the concurrent changes in precipitation have nonnegligible influence on temperature-yield relations. For the country as a whole, 27% of the observed strength of temperature-yield relation relates to the compounding precipitation effects. Further analysis shows that precipitation exerted the compounding effects mainly through its direct influence on yields rather than indirectly from its feedback to temperature. Under 2 and 1.5 degrees C global warming, maize yield for the country as a whole is projected to decrease by -13.53 to -14.37% and -9.02 to -9.29%, respectively, with the magnitude of change depending on the climate model. Around 30% of the benefit by constraining global warming to 1.5 degrees C would be contributed by the compounding precipitation effects, pointing to the important role of precipitation in regulating the impacts of temperature rise on yields. The results can greatly improve our understanding and interpretation of the important but uncertain temperature-yield relations.

Plain Language Summary This paper assesses the precipitation effect in modulating maize yield response to temperature rise in the United States within the context of global warming. Results show that excluding the effect of precipitation does not lead to significant change in the spatial distribution pattern of temperature-driven maize yield changes but can alter the magnitudes substantially. For the country as a whole, concurrent changes in precipitation lead to a decrease in the sensitivity of maize yield to growing-season temperature from -7.48 to -5.47%/k. Constraining global warming to 1.5 degrees C can benefit maize yield by reducing temperature-driven loss from -13.53 to -14.37% under 2 degrees C to -9.02 to -9.29%. However, the estimated benefit by limiting global warming to 1.5 degrees C versus 2 degrees C would be altered considerably, when the effects induced by precipitation changes are excluded. This study highlights the important role of precipitation in regulating temperature impact on crop yields, which are subject to substantial uncertainties.