CONTROL ID: 1504310

TITLE: Evaluation of the seasonal dynamics of photosynthesis and drought stress in CMIP5 models

AUTHORS (FIRST NAME, LAST NAME): James Tremper Randerson¹, Mingquan Mu¹, Brendan M Rogers¹, Nuno Carvalhais², James Ehleringer³, Miguel D Mahecha², Forrest M Hoffman¹, Jannis von Buttlar², Markus Reichstein²

INSTITUTIONS (ALL): 1. Earth System Science Dept, Univ California Irvine, Irvine, CA, United States.
2. Max Planck Institute for Biogeochemistry, Jena, Germany.
3. Department of Biology, University of Utah, Salt Lake, UT, United States.

ABSTRACT BODY: In many northern terrestrial ecosystems, photosynthesis during summer is fueled by the accumulation of snow and soil moisture during winter and spring. With longer growing seasons expected during the next several decades as a consequence of climate warming, increasing drought stress is possible if earlier onset of photosynthesis and transpiration are not balanced by increases in precipitation during the growing season or increases in ecosystem water use efficiency. Here we examined the timing of spring photosynthetic onset in CMIP5 models using eddy covariance observations and atmospheric carbon dioxide mole fraction observations. Our results indicate that many of the CMIP5 models exhibit an early onset bias in photosynthesis and transpiration for the contemporary period. In some models, the early onset of photosynthesis appears to cause ecosystems to more rapidly consume soil moisture reserves, leading to low biases in latent heat fluxes during mid-summer, and as a consequence, greater atmospheric heating and reduced precipitation over the interior of northern continents. We also examined how photosynthesis and drought stress is likely to change during the 21^st century, and assessed how contemporary biases may influence future projections of change. We conclude by describing a new set of physiological mechanisms that may reduce spring photosynthesis biases in climate models.

KEYWORDS: [0475] BIOGEOSCIENCES / Permafrost, cryosphere, and high-latitude processes, [0315] ATMOSPHERIC COMPOSITION AND STRUCTURE / Biosphere/atmosphere interactions.
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CONTACT (NAME ONLY): James Randerson
CONTACT (E-MAIL ONLY): jranders at uci dot edu
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