Abstract 259

Abstract ID: 259

An Emergent Constraint to Improve the Representation of Biosphere-Atmosphere Feedbacks in Earth System Models

Lead Author: Julia Green
University of Arizona, United States of America

Keywords: biosphere-atmosphere feedbacks, emergent constraint, seasonal forecasting, surface temperatures, vegetation

Abstract: Biosphere-atmosphere feedbacks operate on subseasonal to seasonal timescales. Therefore, accurately representing vegetation processes and their interactions with the atmosphere in models is essential to improving subseasonal to seasonal forecasts. One related process, the response of vegetation canopy conductance (gc) to changes in moisture availability (γ_gc^m) is a major source of uncertainty in weather and climate projections. Representing γ_gc^m accurately in Earth System Models (ESMs) is particularly problematic because no regional scale gc observations exist with which to evaluate it. Here, we overcome this challenge by deriving an emergent constraint on γ_gc^m across ESMs from Phase 6 of the Coupled Model Intercomparison Project (CMIP6). We leverage an ensemble of satellite, reanalysis and station-based estimates of surface temperatures, which are physically and statistically linked to γ_gc^m due to the local cooling effect of gc from transpiration. We find that models systemically underestimate γ_gc^m by ~50%, particularly in semi-arid grasslands, croplands, and savannas. Based on the mediating effect of gc on carbon, water and energy fluxes through land-atmosphere interactions, the underestimation of modeled γ_gc^m in these regions contributes to biases in these three fluxes. Our results provide a novel benchmark to improve model representation of vegetation dynamics and biosphere-atmosphere feedbacks in these regions, thus improving forecasting ability under future climate change scenarios.

Yao Zhang (Sino-French Institute for Earth System Science, College of Urban and Environmental Sciences, Peking University, Beijing, China)
Xiangzhong Luo (Department of Geography, National University of Singapore, Singapore; Center for Nature-based Climate Solutions, National University of Singapore, Singapore)
Trevor F. Keenan (Department of Environmental Science, Policy, and Management, University of California Berkeley, Berkeley, California, USA; Climate and Ecosystem Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA)