Soil moisture–atmosphere feedback dominates land carbon uptake variability

Abstract

Year-to-year changes in carbon uptake by terrestrial ecosystems have an essential role in determining atmospheric carbon dioxide concentrations1. It remains uncertain to what extent temperature and water availability can explain these variations at the global scale2–5. Here we use factorial climate model simulations6 and show that variability in soil moisture drives 90 per cent of the inter-annual variability in global land carbon uptake, mainly through its impact on photosynthesis. We find that most of this ecosystem response occurs indirectly as soil moisture–atmosphere feedback amplifies temperature and humidity anomalies and enhances the direct effects of soil water stress. The strength of this feedback mechanism explains why coupled climate models indicate that soil moisture has a dominant role4, which is not readily apparent from land surface model simulations and observational analyses2,5. These findings highlight the need to account for feedback between soil and atmospheric dryness when estimating the response of the carbon cycle to climatic change globally5,7, as well as when conducting field-scale investigations of the response of the ecosystem to droughts8,9. Our results show that most of the global variability in modelled land carbon uptake is driven by temperature and vapour pressure deficit effects that are controlled by soil moisture.

The effects of varying drought-heat signatures on terrestrial carbon dynamics and vegetation composition

“…All results, such as the exact changes in vegetation distribution and carbon uptake, are somewhat sensitive to the choice of the dynamic global vegetation model and the employed climate model. Furthermore, land-atmosphere feedbacks may play an important role (Humphrey et al, 2021), which are not considered in such an offline model setup as we have conducted in this study. A model intercomparison project using our scenarios as forcings for different vegetation models has already been set up and will reveal insights on model differences and their effects on the results.…”

“…Though it is still uncertain exactly how these increases will affect the terrestrial biosphere, there are concerns they might substantially reduce the current terrestrial carbon sink (Reichstein et al, 2013). While coupled models of the land and atmosphere allow for a more complete representation of the feedback processes (Humphrey et al, 2021) than stand-alone land biosphere models, the analysis of results is more complicated for coupled models, since the coupling is different for different models and uncertainties depend not only on the land but also on the atmosphere module.…”

Estimating Agricultural Soil Moisture Content through UAV-Based Hyperspectral Images in the Arid Region

“…Therefore, the purposes of this study are: (1) to assess the effects of FOD technology on UAV-based hyperspectral data; (2) to analyze the capacity of MI for important spectral information; and (3) to estimate the SMC using optimal XGBoost models.…”

“…The soil moisture content (SMC) dominates hydrothermal energy exchange, climate change, and land carbon uptake [1,2]. The limitation of SMC is the connection between atmospheric drying and hydrological responses [3].…”

Nonstationary weather and water extremes: a review of methods for their detection, attribution, and management

“…Nonlinear feedbacks between atmospheric and land surface processes can also lead to varying carbon uptake in vegetation (e.g. soil moisture may alter photosynthesis rates; Humphrey et al, 2021). Afforestation and deforestation affect both floods and droughts -sometimes in more ways than one.…”