PP027-04
Asymmetrical Response of the Continental Water Cycle to Cold and Warm Climates

Thursday, 10 December 2020: 19:12
Virtual
Alexis M Berg, Harvard University, Cambridge, MA, United States, Pierre Gentine, Columbia University, Earth and Environmental Engineering, New York, NY, United States, Benjamin R Lintner, Rutgers, New Brunswick, NJ, United States, Justin Sheffield, University of Southampton, Southampton, United Kingdom and Kaighin A. McColl, Harvard University, Department of Earth and Planetary Sciences and School of Engineering and Applied Sciences, Cambridge, MA, United States
Recorded Presentation
Abstract:
Climate models provide global hydrological simulations under different climate conditions, informing our understanding of the response of the land water cycle to climate change. However, physical interpretation of such simulations remains confounded by the multiplicity of hydrological variables involved and the complex interactions of different climatic and environmental drivers. To provide a more integrated, process-based characterization of the functional response of the global land water cycle to climate change, here we analyze CMIP5 climate model simulations of past and future climate in the framework of the Budyko Relationship, which relates the partitioning of precipitation into evaporation and runoff to available moisture and energy. Of particular interest is if, and how, the shape of this relationship is modulated by climate change.

We identify an asymmetrical response of the Budyko Relationship to past cold climate (the Last Glacial Maximum, LGM), present day climate, and future warm conditions (RCP8.5 scenario): during past warming (LGM to present) precipitation partitioning shifts towards evaporation (away from runoff), thus increasing the convexity of the Budyko Relationship; in contrast, under future warming (present day to RCP8.5) the Budyko relationship remains stationary. Decomposing changes in land evaporation and transpiration shows that this asymmetry reflects greater relative increases in plant transpiration, driven by larger fractional increases in LAI, during past warming; in contrast, future warming sees smaller increases in transpiration, reflecting smaller increases in LAI and greater increases in stomatal resistance. Analysis of idealized CMIP5 experiments further highlights the compensating effects of climate change and CO2’s physiological effect in the Budyko Relationship invariance to future warming: over that range of CO2 increase, the increase in stomatal resistance and associated reduction in transpiration are large enough to offset the warming-induced shifts of precipitation partitioning towards evaporation.

Our results demonstrate a fundamental asymmetry in the continental hydrological response across a range of climatic conditions, driven in large part by non-linearities in the vegetation response to climate and CO2 changes.

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