Identifying contributions of climatic and atmospheric changes to autumn phenology over mid-high latitudes of Northern Hemisphere

Variations in autumn phenology (i.e., the end of growing season, EOS) in recent decades have been suggested to be the dynamic response of terrestrial ecosystems to global environmental change. However, predicting EOS change with climate variation is still challenging, given that there are several environmental factors that can affect EOS apart from warming. In this study, EOS over the Northern Hemisphere (>30 degrees) was calculated by three different extracting methods using the Normalized difference vegetation index (NDVI) records from the Global Inventory Modeling and Mapping Studies third generation (GIMMS3g) during 1982 to 2015. We used partial correlation and partial least-squares regression (PLSR) analyses to investigate the EOS variations in response to five global environmental change factors, including temperature, precipitation, insolation, atmospheric CO2 and nitrogen (N) deposition. We found that about 58.5% (13.6% were significant) of the study area showed earlier EOS trends and 41.5% (10.3% were significant) with later EOS. Warming played a critical role in regulating EOS. The cumulative precipitation during the preseason had the greatest positive impact on EOS in arid/semiarid regions. Sufficient insolation could contribute to the delayed EOS over high latitudes. Compared with climatic factors, EOS also showed high sensitivity to changes in the atmospheric factors, and the dominant control of atmospheric CO2 and N deposition on EOS was found at 25-30% of the areas. Our results confirmed the dominant role of climatic factors in regulating EOS, but other global environmental cues, for instance, elevated atmospheric CO2 concentration and increased atmospheric nitrogen (N) deposition should also be included in the autumn phenological model to further understand the carbon and N cycles of terrestrial ecosystems with climate change.

Automated summary

This study analyzed vegetation index data from the Northern Hemisphere between 1982 and 2015 to investigate the response of autumn phenology to global environmental factors. It found that warming, precipitation, insolation, atmospheric CO2, and nitrogen deposition all play important roles in regulating the end of the growing season. Changes in these factors have varying impacts on different regions, with atmospheric CO2 and nitrogen deposition showing significant control over EOS in some areas.