Resolving effects of leaf pigmentation changes and plant residue on the energy balance of winter wheat cultivation in the ORCHIDEE-CROP model

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Abstract. Crop management impacts climate not only through changes in carbon stocks and greenhouse gas budgets, but also through changes in the heat budget. However, the latter aspect is not yet covered by existing cropping system models. The coupling of dedicated crop models with land surface models may be an attempt to quantify those effects, but is hampered by the simplistic representation of surface albedo as a mix of soil albedo and a static vegetation albedo controlled by vegetation cover. Here, we developed ORCHIDEE-CROP, a land surface model integrating the cropping system model STICS, by incorporating time-varying albedo from crop pigmentation during foliar yellowing and post-harvest crop residue soil cover. We further parameterized the effect of crop residues on surface roughness and soil evaporation affecting the heat budget and partitioning between latent and sensible heat fluxes. Using 10 site simulations, we quantified the impacts of these processes on soil temperature, soil moisture, water and heat fluxes of winter wheat crops. Incorporating foliar yellowing and post-harvest residue cover increased surface albedo by an average of 0.07±0.03 during the foliar yellowing period and 0.02±0.02 during the residue cover period, accordingly inducing surface cooling by −0.42±0.65 °C and -1.39±1.07 °C. During each period, sensible heat flux changed by -0.03±2.34 W m-² and 1.30±11.52 W m-², while latent heat flux decreased by -1.23±1.78 W m-² and -3.59±3.90 W m-². Spatiotemporal variability in these effects was driven by site-specific meteorology and soil properties. Simulations of drying climate scenarios reveal that crop residues left on the field can progressively increase plant available water over multiple years under dry conditions. This study underscores that crop pigmentation and residues significantly modulate surface energy partitioning, and demonstrates the potential of its management for climate mitigation. The refined modelling framework enables simultaneous assessment of the biogeochemical and biophysical impacts of field operations on the Earth System.

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