Summer rain had no clear mean link to the interval from leaf colouring to drop for six tree species at 110 Swiss stations in 1996–2025

We tested whether less summer rain was linked to a shorter interval from 50% leaf colouring to 50% leaf drop. We used 11,096 paired records for six tree species at 110 Swiss stations in 1996–2025. Each station had a fixed nearby weather match. Separate species models included station effects, linear time, July–August temperature and September–October temperature. The equal species mean was 0.43 days shorter per 100 mm less July–August rain. Its 95% interval from 3,999 common three-year block resamples ran from 1.05 days shorter to 0.22 days longer. Joint weather-group and year resampling gave a range from 1.50 days shorter to 0.51 days longer. All planned average checks remained uncertain. Beech had a larger negative estimate, but its interval included zero with common year effects. These models did not establish an average rain link. They do not show a zero effect or identify a drought cause. Rain is a proxy for tree water supply. The recorded thresholds do not measure individual leaf life span or carbon uptake. The package preserves exact source files, provenance, all model results and draws, figures, independent source checks and offline repeat instructions.

phenology · leaf fall · leaf colouring · precipitation · MeteoSwiss · paired observations · block bootstrap · null result