The Yale Interactive terrestrial Biosphere model version 1.0: description, evaluation and implementation into NASA GISS ModelE2

Abstract. The land biosphere, atmospheric chemistry and climate are intricately interconnected, yet the modeling of carbon–climate and chemistry–climate interactions have evolved as entirely separate research communities. We describe the Yale Interactive terrestrial Biosphere (YIBs) model version 1.0, a land carbon cycle model that has been developed for coupling to the NASA Goddard Institute for Space Studies (GISS) ModelE2 global chemistry–climate model. The YIBs model adapts routines from the mature TRIFFID (Top-down Representation of Interactive Foliage and Flora Including Dynamics) and CASA (Carnegie–Ames–Stanford Approach) models to simulate interactive carbon assimilation, allocation, and autotrophic and heterotrophic respiration. Dynamic daily leaf area index is simulated based on carbon allocation and temperature- and drought-dependent prognostic phenology. YIBs incorporates a semi-mechanistic ozone vegetation damage scheme. Here, we validate the present-day YIBs land carbon fluxes for three increasingly complex configurations: (i) offline local site level, (ii) offline global forced with WFDEI (WATCH Forcing Data methodology applied to ERA-Interim data) meteorology, and (iii) online coupled to the NASA ModelE2 (NASA ModelE2-YIBs). Offline YIBs has hourly and online YIBs has half-hourly temporal resolution. The large observational database used for validation includes carbon fluxes from 145 flux tower sites and multiple satellite products. At the site level, YIBs simulates reasonable seasonality (correlation coefficient R > 0.8) of gross primary productivity (GPP) at 121 out of 145 sites with biases in magnitude ranging from −19 to 7 % depending on plant functional type. On the global scale, the offline model simulates an annual GPP of 125 ± 3 Pg C and net ecosystem exchange (NEE) of −2.5 ± 0.7 Pg C for 1982–2011, with seasonality and spatial distribution consistent with the satellite observations. We assess present-day global ozone vegetation damage using the offline YIBs configuration. Ozone damage reduces global GPP by 2–5 % annually with regional extremes of 4–10 % in east Asia. The online model simulates annual GPP of 123 ± 1 Pg C and NEE of −2.7 ± 0.7 Pg C. NASA ModelE2-YIBs is a useful new tool to investigate coupled interactions between the land carbon cycle, atmospheric chemistry, and climate change.