Spatiotemporal characteristics and drivers of Northern Hemisphere phenological change

Determine the spatial and temporal characteristics and the driving mechanisms of vegetation phenological changes—specifically the photosynthetic phenology indicators start of season (SOS), peak of season (POS), and end of season (EOS)—across the Northern Hemisphere.

Background

The paper introduces vegetation photosynthetic phenology as the functional seasonal cycle of plant activity, emphasizing key indicators (SOS, POS, EOS) expressed as day of year, and their importance for carbon and water cycling. Despite numerous large-scale studies, methodological and data limitations have hindered clear understanding of how these phenological metrics vary across space and time and what factors drive their changes in the Northern Hemisphere.

The authors note that commonly used satellite vegetation indices (e.g., NDVI, EVI) and solar-induced chlorophyll fluorescence (SIF) can diverge from actual photosynthetic activity, particularly in evergreen systems, and that coarse spatial resolution and snow contamination further complicate phenology extraction and validation. Additionally, reliance on reanalysis climate data, especially for water-related variables such as vapor pressure deficit and precipitation timing, introduces uncertainties for identifying phenological drivers. The dataset presented aims to address these gaps by leveraging weather-station-scale GPP estimates, but the overarching task of characterizing spatiotemporal patterns and causal drivers remains explicitly stated as unclear.