A new dataset to elucidate inaccurate temperature thresholds masking a hidden source of risk uncertainties in common wheat

Temperatures outside the optimum range for each phenological phase may wreak cereal yield losses. However, there is no consensus on temperature thresholds for assessing thermal stress in wheat. The wide spread use of these thresholds in the scientific literature is hardly ever considered in climate risk assessments. Our review updates the seminal work of Porter and Gawith (1999) by revising thermal stress thresholds, according to the geographical localisation, wheat type, phenological phases and processes involved. A group of 122 publications on the impact of temperature on wheat crops reveals high variability and inconsistencies in the thresholds. We disentangle some of the factors generating this variability and show that when the sample is filtered by geographical localisation, type of common wheat (winter or spring), and biological process (growth or development), the variability decreases within a range of 35–65 % depending on the stress indicator. This variability leads to considerable uncertainty in the estimation of agroclimatic risks to wheat crops. Indeed, a 2°C difference in the stress threshold (25°C vs. 27°C) for the grain-filling phase reduced the heat stress risk (number of days above the threshold) by up to 45 % on average over a 30-year period in France. These results help interpret previous studies by considering how the chosen threshold position within the range of possible values may lead to under or overestimation. We provide the full database from this review, including metadata defining the validity range of each study’s threshold. We recommend that future studies avoid deterministic thresholds and instead use a range of values to capture uncertainty and minimize conflicting conclusions.