Impact of Climate Change on Crop Pests and Diseases: Ensemble Modeling of Time-Varying Weather Effects

The impacts of climate change on crop yields have been extensively studied worldwide, yet the mechanisms underlying changes in yields are not fully understood. This study investigates the relative importance of pest effects using observational data. As weather effects could vary depending on the timing of exposure, I model time-varying weather effects by separating the entire cropping season into thousands of possible growth-stage combinations and select the top-performing models using the cross-validation method. The empirical application reveals that the proposed method achieves a much better prediction performance than conventional methods. By simulating climate change impacts in central and southern Japan, I find that crop yields decrease by approximately 10% and 30% for rice and wheat, respectively. However, pest effects only explain one-tenth of the overall effect of climate change, which suggests that climate change will harm crop growth directly, rather than through disease and pest epidemics.