Observed warming is shrinking favourable daylight windows for outdoor recreation: evidence from sports facilities across France

Dimitri Defrance 

Observed warming is changing not only the severity of heat exposure during outdoor recreation, but also the time of day when thermally favourable conditions remain available. We quantify this emerging temporal constraint across metropolitan France from 1991 to 2025 by combining hourly ERA5-Land meteorology, Wet-Bulb Globe Temperature (WBGT), solar geometry and the national Data ES inventory of 226,516 outdoor sports facilities. We define favourable daylight hours as those simultaneously below a WBGT threshold of 28 °C and within civil twilight, and assess trends using Theil–Sen slopes and Mann–Kendall tests. Favourable daylight time declined or remained unchanged across the entire warm-season grid, with the strongest contractions in southern and south-western France and during summer afternoons. In Mediterranean France, the largest recent declines occurred around 14:00–17:00 local time, progressively shifting favourable conditions towards the cooler margins of the day. Regional exposure was highly uneven: more than 60% of outdoor facilities in Nouvelle-Aquitaine and Occitanie were located in highly exposed cells. Current lighting only partly offsets this constraint, leaving substantial shares of highly exposed facilities unlit. Differences among sports largely reflected the geography of facility provision rather than intrinsic thermal sensitivity. These results show that climate change is reducing the temporal accessibility of outdoor recreation and that adaptation capacity is spatially uneven. Incorporating time-of-day into recreation planning could help identify where rescheduling, shading, modified opening hours or targeted infrastructure adaptation are most needed.