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PI-Submitted Research Highlights for
Terrestrial Ecosystem Science Program

Increasing Impacts of Extreme Droughts on Vegetation Productivity Under Climate Change

Chonggang Xu

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November 25, 2019

Multimodel analysis suggests increases in the frequency of extreme droughts and the magnitude of their effects on plant growth.

The Science
This research showed an increasingly stronger impact on terrestrial gross primary production (GPP) by extreme droughts than by mild and moderate droughts over the 21st century. Specifically, the percentage contribution by extreme droughts to the total GPP reduction associated with all droughts was projected to increase from ~28% during 1850–1999 to ~50% during 2075–2099.

The Impact
Even though higher carbon dioxide (CO2) concentrations in future decades can increase GPP, low soil water availability and disturbances associated with droughts could reduce the benefits of such CO2 fertilization. This study conducted the first global analysis to quantify potential impacts of drought on future GPP, an assessment which could guide future modeling and field experiments.

Summary
Terrestrial GPP is the basis of vegetation growth and food production globally and plays a critical role in regulating atmospheric CO2 through its impact on ecosystem carbon balance. In this study, scientists from the Next-Generation Ecosystem Experiments (NGEE)–Tropics project and Los Alamos National Laboratory (LANL) analyzed outputs of 13 Earth system models to show an increasingly stronger impact on GPP by extreme droughts than by mild and moderate droughts over the 21st century. The droughts were defined on the basis of root-weighted plant-accessible water. Due to a projected dramatic increase in the frequency of extreme droughts, the magnitude of globally averaged reductions in GPP associated with extreme droughts was projected to be nearly tripled by the last quarter of this century (2075–2099) relative to that of the historical period (1850–1999) under both high and intermediate greenhouse gas (GHG) emission scenarios. By contrast, the magnitude of GPP reductions associated with mild and moderate droughts was not projected to increase substantially. These drought impacts were widely distributed with particularly high risks for the Amazon, Southern Africa, Mediterranean Basin, Australia, and the southwestern United States. This analysis indicates a high risk of extreme droughts to the global carbon cycle with atmospheric warming; however, this risk can be potentially mitigated by positive anomalies of GPP associated with favorable environmental conditions.

Contacts
BER Program Manager
Daniel Stover
U.S. Department of Energy Office of Science,
Office of Biological and Environmental Research
Earth and Environmental Systems Sciences Division (SC-33.1)
Environmental System Science
daniel.stover@science.doe.gov

Principal Investigator
Chonggang Xu
Los Alamos National Laboratory
Los Alamos, NM
cxu@lanl.gov

Funding
This work was funded by (1) the Next-Generation Ecosystem Experiments (NGEE)–Tropics project and the Survival/Mortality project, both sponsored by the Terrestrial Ecosystem Science program of the U.S. Department of Energy’s (DOE) Office of Biological and Environmental Research within the DOE Office of Science; (2) the Laboratory Directed Research and Development program of Los Alamos National Laboratory; and (3) the University of California’s Laboratory Fees Research Program (Grant No. LFR-18-542511). Also used was the DOE Program for Climate Model Diagnosis and Intercomparison (PCMDI), which provides coordinating support and led development of software infrastructure in partnership with the Global Organization for Earth System (GOES) science portals.

Publications
Xu, C., N. G. McDowell, R. A. Fisher, L. Wei, S. Sevanto, E. Weng, and R. Middleton. “Increasing impacts of extreme droughts on vegetation productivity under climate change.” Nature Climate Change 9, 948–53 (2019). [DOI:10.1038/s41558-019-0630-6].

Related Links

The main funding source is NGEE tropics. We  also used the Department of Energy’s Program for Climate Model Diagnosis and Intercomparison provides coordinating support and led development of software infrastructure in partnership with the Global Organization for Earth System Science Portals.

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