Weakening greening trend in the late growing season across mid-to-high latitudes in the Northern Hemisphere and its drivers
Wen Zhang, The University of Arizona, wenzhang1@arizona.edu (Presenter)
David Moore, University of Arizona, davidjpmoore@email.arizona.edu
William Kolby Smith, University Of Arizona, wksmith@email.arizona.edu
The high northern latitudes ecosystem (above 30°N) has an enhanced greening trend during the early and peak growing season periods since the 1980s, but the greenness trend during the late growing season period and its underlying mechanisms in these regions are not yet fully understood. Here, we used a satellite-derived leaf area Index (LAI) and combined multi-regression analysis with machine learning (random forests) to assess the greenness trend changes and the main environmental drivers during the late growing season period from 2000-2018. Overall, we demonstrated a weakening greening trend during the late growing season period compared to that in the early- and peak-growing season period, due to 10.2 % of the study area exhibiting a significant browning trend. Surprisingly, the browning trend was more significant in humid regions rather than in drier regions. The browning trend in the late season is due to accumulated soil moisture deficit in the peak-growing season period. However, state-of-the-art land surface models do not simulate the observed spatial greening and browning distributions, though they did reproduce the area-averaged weakening trends. Consequently, they underestimated the soil moisture constraints on vegetation greening trends during this period. The browning trend induced by drying soil over Northern Hemisphere, which is likely to persist into the drier future, will be a major driver of greenness changes with consequences for the global carbon, water, and energy balance.
Associated Project(s):
Poster Location ID: 3-39
Presentation Type: Poster
Session: Poster Session 3
Session Date: Thu (May 11) 3:00-5:00 PM
CCE Program: TE