Mixed Land Cover Maximizes Surface Cooling in India: An ICON Model Energy-Balance Attribution Study

India is experiencing rapid land-use transitions through cropland expansion and afforestation, which modify surface properties such as albedo and evapotranspiration and, in turn, influence land surface temperature. What remains unclear, however, is how much of the resulting temperature change is driven by individual surface energy balance components, and whether cropland expansion and afforestation produce symmetric or distinct biogeophysical responses, a question we address using idealised ICON model experiments. Therefore, we conduct three land-cover change experiments using the ICON Earth system model and follow the AMIP protocol: (i) a control simulation mirroring the historical land cover change until present-day (CTRL), (ii) a forest-to-cropland experiment (F2C) where all tropical deciduous forests are replaced by cropland, and (iii) a cropland-to-forest experiment (C2F) in which all croplands are replaced by tropical deciduous forest. All simulations are global and span the period 1850-2014 (165 years).

Preliminary results show that, relative to the CTRL simulation, the F2C experiment exhibits a long-term mean surface warming of 0.26°C, while the C2F simulation shows a weaker warming of 0.05 °C over India. Surface energy balance decomposition, which quantifies the contributions of individual radiative and turbulent flux components (shortwave radiation, longwave radiation, latent heat flux, sensible heat flux, ground heat flux, and albedo) to surface temperature change, indicates that the F2C simulation leads to surface warming relative to CTRL (+0.26 °C in the model, compared to +0.55 °C inferred from energy balance attribution). This difference between the attributed and model-simulated warming arises because the attribution estimate sums individual flux-driven contributions, whereas the model-diagnosed temperature additionally reflects nonlinear feedbacks and heat storage effects. Warming is primarily due to increased net longwave radiation (+0.46 °C), decreased latent heat flux (+0.23 °C) and enhanced sensible heat flux (+0.21 °C), partially offset by albedo-driven cooling (-0.36 °C). In contrast, C2F produces weaker warming relative to CTRL (+0.05 °C in the model; +0.07 °C from attribution), dominated by reduced surface albedo (+0.70 °C) and increased net shortwave absorption (+0.06 °C), despite enhanced latent heat flux. C2F exhibits the highest latent heat flux (55.87 W m^-2) and lowest downward longwave radiation (61.92 W m^-2), favouring cooling, but this is counteracted by low albedo (0.17), high net shortwave radiation (167.87 W m^-2), and elevated sensible heat flux (47.30 W m^-2). Trend analysis further indicates that C2F warms slightly faster (0.0062 °C yr^-1) than CTRL (0.0059 °C yr^-1) and F2C (0.0055 °C yr^-1), mainly due to a persistently decreasing albedo. Overall, our results show that neither complete afforestation nor extensive cropification maximizes surface cooling over India. Instead, a mixed land-cover configuration optimizes competing biogeophysical processes that regulate surface temperature, highlighting the importance of explicitly accounting for surface energy balance mechanisms in land-use planning.