Distribution and Attribution of Earlier Start of the Growing Season over the Northern Hemisphere from 2001–2018

Abstract

The start of the growing season (SOS) is a vital ecological indicator for climate change and the terrestrial ecosystem. Previous studies have reported that the SOS over the Northern Hemisphere (NH) has experienced remarkable changes in the past few decades. However, because of the different spatial and temporal coverages of existing SOS studies, a coherent and robust account for SOS changes in the NH has been lacking. Using satellite-retrieved vegetation-phenology datasets, ground observations, and several auxiliary datasets, this study evaluated the performance of the latest MODIS vegetation-dynamics dataset (MCD12Q2-C6) and explored the distribution and attribution of the SOS to climate change over the NH for the period 2001–2018. The validation results using the Chinese Ecosystem Research Network (CERN) and Lilac-leafing observations (Lilac) displayed that the MCD12Q2-C6 has a good performance in SOS monitoring over the NH mid-latitudes. Meanwhile, evidence from MCD12Q2-C6 pointed out that the SOS was advanced by 2.08 days on average over the NH during 2001–2018, especially for Europe, China, and Alaska, United States. In addition, detailed-sensitivity analysis showed that the increased surface air temperature (Ts) (−1.21 ± 0.34 days °C−1) and reduced snow-cover fraction (Sc) (0.62 ± 0.29 days%−1) were the key driving factors of the observed SOS changes over the NH during 2001–2018. Compared with Ts and Sc, the role of total precipitation (Pt) was minor in dominating the spring vegetation-phenology changes at the same period. The findings of this study contribute to our understanding of the responses of SOS to the competing changes of Ts, Pt, and Sc over the NH.

Impact of Preseason Climate Factors on Vegetation Photosynthetic Phenology in Mid–High Latitudes of the Northern Hemisphere

“…However, it is noteworthy that, at a regional level, a distinct trend of a delayed SOS has been evident across the majority of the regions in northeastern North America in recent decades. This observation aligns with previous research findings, indicating a gradual weakening of the carbon sink capacity in these regions [25].…”

“…Utilizing long-term photosynthetic phenology data, we have identified a significant advancement in the SOS within northern terrestrial ecosystems. This observation is based on a comprehensive analysis of photosynthetic phenology, aligning with prior studies that employed greenness indicators to investigate a similar trend [25,26]. In particular, Chen et al ( 2022) found a slightly different magnitude, noting a 2.08-day average advancement in the SOS over the NH during 2001-2018.…”

“…For instance, our analysis was primarily focused on the partial correlations of mean temperature, diurnal temperature range, and precipitation with vegetation photosynthetic phenology. We did not consider additional climatic variables such as cloud cover, solar radiation, or snow melt patterns, nor variations in vegetation types or human interventions [1,25,42,44]. Since our study predominantly relied on existing global climate databases, integrating emerging microclimate datasets in future work could enhance the accuracy of simulations and predictions regarding the impact of regional climate change on vegetation phenology [56].…”