Northern Hemisphere Land–Atmosphere Feedback from Prescribed Plant Phenology in CESM

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Abstract Plant phenology influences both the terrestrial carbon cycle and land–atmosphere interactions and, therefore, can potentially modify large-scale circulations in the atmosphere. However, considerable discrepancies are present among models and between model simulations and observations of plant phenology, adding large uncertainties to future climate projections. Here, we modified plant phenology in the Northern Hemisphere in the Community Earth System Model and conducted simulations to characterize how differences in plant phenology influence land–atmosphere coupling. Plant phenology changes the land surface and land–atmosphere interactions by directly modulating absorbed solar radiation and evapotranspiration and indirectly modifying cloud feedback and snow–albedo feedback. Over the Northern Hemisphere, the largest effects occur from March to June when seasonal deciduous phenology is modified from satellite-derived values to model simulations, which results in a >3 K increase in surface temperature that propagates to 500 hPa (∼5-km height). Phenology-induced changes in canopy evapotranspiration and surface temperature depend on soil moisture availability during the growing season. Surface temperature decreases significantly due to increasing latent heat flux and cloud reflection where soil moisture is abundant, while soil moisture control over evapotranspiration increases, and surface temperature remains little changed or even increases in more arid regions. Characterizing the influence of phenology on biogeophysical processes is critical, as significant impacts are present both at the land surface and in the atmospheric layers above. Significance Statement Plant phenology influences both biogeochemical and biogeophysical processes in climate models. However, considerable discrepancies exist between satellite-derived phenology and state-of-the-art climate model simulations, and their influences on land–atmosphere coupling remain unclear. Here, we prescribe phenology discrepancies in different phenology plant function types (PFTs) to assess their influences on Earth’s system and find significant PFT-dependent impacts. The largest impacts are in high-latitude regions dominated by seasonal deciduous PFTs in late winter to spring when increasing plant activity, cloud feedback, and snow–albedo feedback all cause increased surface temperature. Growing-season temperature decreases where soil moisture is abundant due to increasing evapotranspiration and cloud feedback. Understanding the potential influences of phenology discrepancies is critical for disentangling phenology-induced changes and uncertainties in future climate projections.

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