Exploring the environmental drivers of vegetation seasonality changes in the northern extratropical latitudes: a quantitative analysis * * This manuscript has been authored by UT-Battelle LLC under Contract No. DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable,

Abstract

Vegetation seasonality in the northern extratropical latitudes (NEL) has changed dramatically, but our understanding of how it responds to climate change (e.g. temperature, soil moisture, shortwave radiation) and human activities (e.g. elevated CO2 concentration) remains insufficient. In this study, we used two remote-sensing-based leaf area index and factorial simulations from the TRENDY models to attribute the changes in the integrated vegetation seasonality index (S), which captures both the concentration and magnitude of vegetation growth throughout the year, to climate, CO2, and land use and land cover change (LULCC). We found that from 2003 to 2020, the enhanced average S in the NEL (MODIS: 0.0022 yr−1, p < 0.05; GLOBMAP: 0.0018 yr−1, p < 0.05; TRENDY S3 [i.e. the scenario considering both time-varying climate, CO2, and LULCC]: 0.0011 ± 7.5174 × 10−4 yr−1, p < 0.05) was primarily determined by the elevated CO2 concentration (5.3 × 10−4 ± 3.8 × 10−4 yr−1, p < 0.05) and secondly controlled by the combined climate change (4.6 × 10−4 ± 6.6 × 10−4 yr−1, p > 0.1). Geographically, negative trends in the vegetation growth concentration were dominated by climate change (31.4%), while both climate change (47.9%) and CO2 (31.9%) contributed to the enhanced magnitude of vegetation growth. Furthermore, around 60% of the study areas showed that simulated major climatic drivers of S variability exhibited the same dominant factor as observed in either the MODIS or GLOBMAP data. Our research emphasizes the crucial connection between environmental factors and vegetation seasonality, providing valuable insights for policymakers and land managers in developing sustainable ecosystem management strategies amidst a changing climate.