Unraveling the impact of environmental factors on wheat yield across the European Union via explainable machine learning

Accurately predicting crop yield and identifying its response to environmental drivers are critical for ensuring food security and optimizing commodities trading financial operations under climate change. Soft wheat is the most widely cultivated crop across the European Union (EU). While studies have assessed the impacts of environmental factors locally, a comprehensive continental-scale analysis of their impacts on soft wheat yield across the EU remains unexplored. To address this research gap, we evaluated the performance of six machine learning models in predicting the Nomenclature of territorial units for statistics (NUTS)-level wheat yield of the EU from 2000 to 2020 using a suite of comprehensive environmental factors, including air temperature, precipitation, solar radiation, soil moisture, and air humidity. Using explainable machine learning, we quantified the importance of these variables in explaining the spatial and temporal variations of wheat yield across the EU throughout the growing seasons. The results demonstrated that the bidirectional long short-term memory (BiLSTM) model outperformed other models with R$^2$, RMSE, NRMSE, and Bias of 0.75, 1.17 t/ha, 20.86% and −0.01 t/ha, respectively, using the Leave-One-Year-Out (LOYO) cross-validation approach. ... mehrFrom the SHapley Additive exPlanation (SHAP) analysis, we found that: (1) solar radiation throughout the growing season, air temperature in winter, vapor pressure deficit from April to June, and soil water content in autumn and early winter contributed significantly to yield variations; (2) In the southern and eastern EU, wheat often suffers from water stress during most of the growing season; While in the southern EU, heat stress caused by high solar radiation tends to lower wheat yield, and in the northern and eastern EU, cold winter lead to low wheat yields. By leveraging explainable machine learning, this study reveals the impact of various environmental factors on EU wheat yield during the past two decades, offering valuable insights into agricultural management and financial operations in commodities trading under climate change.