Abrupt shifts in phenology and vegetation productivity under climate extremes

Authors: MA, X. - University Of Technology Sydney; HUETE, A. - University Of Technology Sydney; Moran, Mary; Ponce Campos, Guillermo; EAMUS, D. - University Of Technology Sydney

Submitted to: Journal of Geophysical Research-Biogeosciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/11/2015
Publication Date: 10/21/2015
Citation: Ma, X., Huete, A., Moran, M.S., Ponce Campos, G.E., Eamus, D. 2015. Abrupt shifts in phenology and vegetation productivity under climate extremes. Journal of Geophysical Research-Biogeosciences. 120:2036–2052. https://doi.org/10.1002/2015JG003144.
DOI: https://doi.org/10.1002/2015JG003144

Interpretive Summary: Global warming is predicted to increase climate variability and the frequency and severity of droughts, but the effects of these extreme climate events on vegetation are still uncertain. We investigated the impacts of early 21st century climatic extremes on vegetation in southeastern Australia using satellite images. We found abrupt changes in the length of growing seasons and vegetation growth under drought and wet extremes, with widespread collapse in seasonal trends during drought years. Further, we found that vegetation in semi-arid climates exhibited the largest sensitivity to climatic variations. This unexpected result suggests that semi-arid ecosystems are most vulnerable to climatic extremes and will experience severe loss of resilience with future mega-drought events. We concluded that the current drying trend in the Southern Hemisphere will result in loss of a large land carbon sink during future wet periods.

Technical Abstract: Amplification of the hydrologic cycle as a consequence of global warming is predicted to increase climate variability and the frequency and severity of droughts. Predicting how ecosystems will be affected by climate change requires not only reliable forecasts of future climate, but also observational evidence of ecosystem response to current and past climate conditions to synthesize our knowledge. Recent climatic extremes involving large-scale drought and flooding over numerous continents provide unique opportunities to understand ecosystem responses to intensification of the water cycle under global warming. In this study, we investigated the impact of climatic extremes during the early 21st century on phenology and vegetation productivity in southeastern Australia (SEA) using Moderate Resolution Imaging Spectroradiometer (MODIS) Enhanced Vegetation Index (EVI) and Standardized Precipitation-Evapotranspiration Index (SPEI). Results revealed dramatic impacts of hydroclimatic variations on phenology and vegetation productivity, with abrupt between year changes in phenology. Drought resulted in widespread reductions or collapse in the normal patterns of seasonality such that in many cases there was no detectable phenological cycle during drought years. Regional vegetation productivity was reduced by 21% in the extreme drought year of 2002, but increased by 20% in the wetter-than-average year of 2010, relative to the decadal average. Importantly, across the full-range (arid to humid) of climates examined, we found semi-arid ecosystems exhibiting the largest sensitivity to hydroclimatic variations, exceeding that of arid ecosystems. This unexpected result demonstrated that semi-arid ecosystems are most vulnerable to climatic extremes and most likely to experience severe loss of ecosystem resilience with future mega-drought events. Meanwhile, we found a skewed distribution of hydroclimatic sensitivity as a function of aridity further suggests that current drying trends in semi-arid regions will reduce hydroclimatic sensitivity with corresponding loss of the large carbon sink during future wet periods, hence of global biogeochemical significance.