The impacts of aridification on land surface phenological changes in the farming-pastoral ecotone of northern China based on the climatic zoning method.

Key phenological periods of vegetation (such as the start (SOS) and end (EOS) of the growing season) are affected by climate change and human activities. However, the impact of aridification on these phenological responses is still unclear. In the farming-pastoral ecotone of northern China (FPENC), which is plagued by severe aridification, the climate change-dominant aridification zone (CDA), human activity-dominant aridification zone (HDA), and compound-dominant aridification zone (CHDA) were differentiated, and their phenological responses to different aridification types were studied via multiyear remote sensing inversion and meteorological data. Our results suggest that aridification significantly shortened the vegetation growing season, i.e., the SOS tended to be delayed (0.4–5.12 d/10a), and the EOS tended to be advanced (0–2.89 d/10a). In addition, the negative impact of CHDA, which had the highest aridification intensity, on phenological change was 3 to 4 times than that of CDA and twice than that of HDA. Thresholds were found in the phenological responses to climate change: in aridification areas, where the interannual warming rate exceeded 0.02–0.04 °C/a or the increased rate of interannual precipitation was less than 8 mm/a, prolonged growing seasons transitioned to shortened seasons. Furthermore, there was a nonlinear relationship between human activity contributions and phenological changes. When human activity contributions were between 40 and 70%, the growing season was significantly shortened. The extent of the SOS delay for cultivated land was greater than that for grassland, while the extent of the EOS advance was less for cultivated land than for grassland. Within the same climate zone, cultivated land phenological changes were stabilized by human activities, while grassland phenological changes under natural conditions were more severe and accompanied by signs of vegetation degradation. This study provides incremental knowledge for understanding the impacts of aridification on phenology and for adapting to aridification. [ABSTRACT FROM AUTHOR]