Fig. 4

Correlograms of the yearly trends observed for the temperature averaged on a mobile window of 3, 4, or 5 weeks. Each pixel (x, y) corresponds to a temperature averaging window spanning y weeks (vertical axis) after the date x (horizontal axis). The color of a pixel (x, y) corresponds to the correlation coefficient between the years and the mean temperature on the corresponding temperature averaging window (starting at the date x and spanning y weeks after). Significant (p value < 0.05) correlation coefficients are indicated by a cross. A red square corresponds to a positive correlation and a blue square to a negative correlation. Three periods were characterized by a significant increase: ~April (e.g., from DoY 92–120, 0.18 °C year⁻¹), in ~June (e.g., from DoY 141–169, 0.10 °C year⁻¹), and in ~November (e.g., from DoY 295–323, 0.14 °C year⁻¹)