Multimodel simulations revealed strong spatial heterogeneity in temperature‐, photoperiod‐ and moisture‐driven modes of autumn phenology in Northern Hemisphere grasslands (25° N–55° N)

Abstract Autumn phenology plays a critical role in regulating growing season length and matter and energy exchanges in terrestrial ecosystems. The climate‐driven mechanism of the grassland autumn phenology process and its spatial distribution patterns at the hemispheric scale are, however, still poorly understood. In this study, we employed 17 existing and modified models to simulate the satellite‐derived end‐of‐season (EOS) over northern mid‐latitude grasslands (25° N–55° N), aiming to determine how grassland autumn phenology responds to individual and combined changes in low temperature, photoperiod, and water supply. The results showed that the prediction accuracy of EOS based on models driven by daily minimum temperature is slightly superior to that of the counterparts forced by daily average temperature. The model modified with water content as a regulatory factor of leaf senescence rate determined by low temperature and photoperiod performed best (root‐mean‐square error, 10.4 days; correlation coefficient, 0.38) on average. The autumn phenology process in 68.4% of grassland areas was better simulated by the models that incorporated water conditions. Spatially, optimal models jointly forced by low temperature, photoperiod, and water supply occupied 61.4% of the North American grasslands, 58.5% of the Central‐West Asian grasslands, and 42.1% of the Mongolian grasslands. Grasslands on the Tibetan Plateau were primarily forced by the associated effects of low temperature and photoperiod. Further analysis revealed that low temperature‐photoperiod driven models and low temperature‐photoperiod‐moisture driven models were mostly distributed in relatively hotter and wetter grasslands, while optimal models forced solely by low temperature were largely concentrated in those grassland areas with cooler and drier autumn. Overall, this study highlights the complex patterns and spatial heterogeneity of environmental control on autumn phenology in the Northern Hemisphere grasslands, which could shed light on global grassland development investigation.