Summer rain deficits gave no clear change in autumn warmth slopes of leaf colour-to-fall gaps in four Swiss samples, 1951-2024

We tested whether summer rain deficits change the autumn warmth response of the gap from leaf colour to leaf fall. We used 6,061 paired beech and horse chestnut records at 70 Swiss stations in 1951-2024. We used the same 114 site-species series in two periods and two regions. Weather came from E-OBS v31.0e. Models controlled site-species differences, species-specific time blocks, summer warmth and autumn rain. Each series had equal total weight. The four interaction estimates were -0.33 to +0.09 days per C per standard deviation of summer rain deficit. All four 95 percent intervals, with a correction for four tests, included zero. The tests did not show a repeated interaction. Tests with separate species, site trends, year effects and longer records also left the interaction uncertain. In 1988-2024, both colour and fall dates had positive warmth slopes in both regions, but their gap slopes were uncertain. The primary intervals permit changes of about one day per C per deficit unit in either direction. These data do not prove that the effect is absent. Missing visits, tree changes, coarse weather and a common observation network limit the test. This study measures visible seasonal stages. It does not identify a causal climate effect, air pollution effects or biodiversity loss. The package contains code, source hashes, figures, aggregate results and independent numerical checks. External weather and joined record tables stay outside the signed package under their source terms.

autumn phenology · leaf colour · leaf fall · summer rain deficit · compound weather · E-OBS · MeteoSwiss · observation bias · regional replication · null result