Less summer rain had no clear link to autumn greenness dates at 43 PhenoCam sites in 2008–2024

We tested whether less summer rain was associated with earlier autumn canopy greenness loss. We used 414 camera-years at 43 deciduous broadleaf PhenoCam sites in North America in 2008–2024. The fixed linear model used June–August rain, summer and autumn temperature, site effects and year effects. Halving summer rain was associated with a 1.63-day later falling 50% greenness date. The approximate 95% interval was 2.39 days earlier to 5.17 days later. We used 4,999 refits that resampled 13 spatial cells and 17 years. The 25% date, 10% date and late-fall duration also had intervals that included zero. All ten fixed midpoint checks had intervals that included zero. A post-plan check added 26 valid records for 2025 and gave +1.40 days (−2.26 to +5.31). With year resampling alone, the midpoint interval was +0.04 to +3.76 days. Thus, the uncertainty estimate depends on the resampling unit. The result does not establish equal dates or no drought response. It applies to selected camera records with autumn midpoints in September–December. Summer losses before September, rare drought thresholds, soil water and species responses were not tested. The package has unchanged source files, source hashes, selection records, all estimates, bootstrap samples, figures and code. An independent CSV rebuild and full matrix calculation matched the final results.

phenology · PhenoCam · summer precipitation · autumn greenness · Daymet · spatial bootstrap · reproducibility