Carbon sources and sinks of North America as affected by major drought events during the past 30 years

Zelalem A. Mekonnen, Robert F. Grant, Christopher Schwalm

Research output: Contribution to journalArticlepeer-review

14 Scopus citations


The North American (NA) terrestrial biosphere has been a long-term carbon sink but impacts of climate extremes such as drought on ecosystem carbon exchange remain largely uncertain. Here, changes in biospheric carbon fluxes with recent climate change and impacts of the major droughts of the past 30 years on continental carbon cycle across NA were studied using a comprehensive mathematical process model, ecosys. In test of these model responses at continental scale, the spatial anomalies in modeled leaf area indices, fully prognostic in the model, from long-term (1980–2010) means during major drought events in 1988 and 2002 agreed well with those in AVHRR NDVI (R2 = 0.84 in 1988, 0.71 in 2002). Net ecosystem productivity (NEP) modeled across NA declined by 92% (0.50 Pg C yr−1) and 90% (0.49 Pg C yr−1) from the long-term mean (+0.54 Pg C yr−1), in 1988 and 2002 respectively. These significant drops in NEP offset 28% of the carbon gains modeled over the last three decades. Although the long-term average modeled terrestrial carbon sink was estimated to offset ∼30% of the fossil fuel emissions of NA, only 0.03% and 3.2% were offset in 1988 and 2002 leaving almost all fossil fuel emissions to the atmosphere. These major drought events controlled much of the continental-scale interannual variability and mainly occurred in parts of the Great Plains, southwest US and northern Mexico. Although warming in northern ecosystems caused increasing carbon sinks to be modeled as a result of greater gross primary productivity with longer growing seasons, elsewhere in the continent frequent drought events of the past 30 years reduced carbon uptake and hence net carbon sinks of the NA.

Original languageEnglish (US)
Pages (from-to)42-56
Number of pages15
JournalAgricultural and Forest Meteorology
StatePublished - Oct 15 2017


  • Carbon source and sink
  • Climate change
  • Ecosystem modeling
  • North America carbon cycle
  • North America drought
  • ecossys

ASJC Scopus subject areas

  • Forestry
  • Global and Planetary Change
  • Agronomy and Crop Science
  • Atmospheric Science


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