Long-lead Stratospheric Precursors of European Vegetation Dynamics and Crop Yield

Abstract. Modes of atmospheric variability in the North Atlantic are known to influence vegetation activity across Europe, yet it remains unclear whether they enable long-lead predictions of vegetation dynamics for several months ahead in time. Identifying such early precursors of vegetation phenology is essential for improving crop yield predictions under changing climatic conditions. Here, we show that the winter Northern Hemisphere stratospheric polar vortex (SPV), a well documented large-scale driver of European winter weather, influences vegetation dynamics across Europe from winter to summer. Comparing years characterized by weak and strong winter-mean SPV conditions in satellite-derived vegetation greenness, atmospheric reanalysis, and crop yield data, we identify two pathways through which the SPV shapes European summertime vegetation. First, the SPV directly modulates winter weather, with implications for vegetation in the early growing season that can persist into summer through lagged effects. Second, the winter SPV modulates the timing of springtime SPV breakdown, which in turn shifts probabilities of hazards to vegetation activity like frost after bud burst and soil moisture anomalies. In France's breadbasket region, weak wintertime SPV conditions delay growing season onset by up to three weeks relative to strong SPV conditions, while an associated delayed springtime SPV breakdown reduces the risk of soil moisture anomalies up to 100 %, increasing the summertime vegetation peak. Hence, nearly all weak SPV years in our record show positive winter and spring crop yield anomalies in this region. Conversely, strong wintertime SPV advances growing season onset, while the springtime SPV breakdown in these years increases risk of soil moisture extremes up to threefold, risking crop loss. Our results identify the winter SPV as a previously underappreciated long-lead precursor of vegetation and crop productivity anomalies in Europe, offering potential predictability several months ahead for agricultural applications.