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Title: Plant responses to increasing CO 2 reduce estimates of climate impacts on drought severity

Rising atmospheric CO 2 will make Earth warmer, and many studies have inferred that this warming will cause droughts to become more widespread and severe. However, rising atmospheric CO 2 also modifies stomatal conductance and plant water use, processes that are often are overlooked in impact analysis. We find that plant physiological responses to CO 2 reduce predictions of future drought stress, and that this reduction is captured by using plant-centric rather than atmosphere-centric metrics from Earth system models (ESMs). The atmosphere-centric Palmer Drought Severity Index predicts future increases in drought stress for more than 70% of global land area. This area drops to 37% with the use of precipitation minus evapo-transpiration (P-E), a measure that represents the water flux available to downstream ecosystems and humans. The two metrics yield consistent estimates of increasing stress in regions where precipitation decreases are more robust (southern North America, northeastern South America, and southern Europe). The metrics produce diverging estimates elsewhere, with P-E predicting decreasing stress across temperate Asia and central Africa. The differing sensitivity of drought metrics to radiative and physiological aspects of increasing CO 2 partly explains the divergent estimates of future drought reported in recent studies. Further, use of ESMmore » output in offline models may double-count plant feedbacks on relative humidity and other surface variables, leading to overestimates of future stress. The use of drought metrics that account for the response of plant transpiration to changing CO 2, including direct use of P-E and soil moisture from ESMs, is needed to reduce uncertainties in future assessment.« less
Authors:
ORCiD logo [1] ; ORCiD logo [2] ;  [3] ;  [4]
  1. Univ. of Washington, Seattle, WA (United States). Dept. of Atmospheric Sciences and Dept. of Biology
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Computer Science & Mathematics Division and Environmental Sciences Division
  3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Climate & Ecosystem Sciences Division
  4. Univ. of California, Irvine, CA (United States). Dept. of Earth System Science
Publication Date:
Grant/Contract Number:
AC02-05CH11231; AGS-1321745
Type:
Accepted Manuscript
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Volume: 113; Journal Issue: 36; Journal ID: ISSN 0027-8424
Publisher:
National Academy of Sciences, Washington, DC (United States)
Research Org:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23); National Science Foundation (NSF)
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; drought; global warming; climate impact; evaporation; global hydrology
OSTI Identifier:
1377477