Spatiotemporal dynamics of heat stress and cold stress on UK rapeseed cropping over 1961-2020.

Most temperature stress research in oil crops has focused on either heat or cold stress with analyses of the effects of both in combination rare. For the UK, neither the spatiotemporal hot spots of temperature stressed arable areas nor the comparative trends of heat and cold stresses for rapeseed cropping under climate change are understood. This study investigated the spatiotemporal heat and cold stresses for UK rapeseed over 1961–2020, and quantified the normalized rapeseed production loss index (fRPL) induced by heat stress during flowering. Stress indices including a literature derived heat stress index (fHS), cold degree days (CDD), with historical land cover and crop productivity data were used to comparatively study both stresses and to estimate fRPL. Results showed increasing fHS, particularly during flowering (April to May) and main yield-forming reproductive stages (spanning flowering through pod and seed development from April to July) over the study period, with fHS being negatively correlated with latitude. The decreasing values of CDD and frequency of cold stress suggest cold stress decreased during the flowering, vegetative (September to November) and reproductive stages. Notably, this study observed that annually at the UK level heat stress was increasing at a faster rate than cold stress was decreasing during flowering. The increasing values of fRPL, with significant differences between decades and regions, suggested an increasing production loss. These results presented a potentially trend of increasing heat stress impacts on future rapeseed production and further work is required to understand the specific impacts and mitigation strategies for addressing UK food security.