POLICE

Parameter Optimisation of a terrestrial biosphere model to Link processes to Inter annual variability of Carbon fluxes in European forest Ecosystems

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 Obiettivo del progetto (Objective)

'Inter annual variations of net ecosystem carbon exchange (NEE), driven by weather and climate, are known to contribute to variation in the annual growth rate of atmospheric CO2 globally, but little is known about the underlying processes in each region. Better ability to predict future atmospheric CO2 levels and climate change should thus be gained by understanding the current inter annual variation in the biotic response to environmental forcing. In this context, I propose to assess, using a state of the art data assimilation approach, the impact of extreme climate spells, such as the summer 2003, versus the one of “normal” year-to-year climate variations on the processes which control the European carbon balance. This knowledge will be propagated into better future projections of the European carbon balance. Overall, the scientific objectives of the project will be primarily investigated using an parameter optimisation approach. Estimation of the process-based ecosystem parameters using radiation, sensible heat, latent heat, and CO2 exchanges at several ecosystem sites (forest) will help to improve the simulation of inter annual variations in terrestrial CO2 fluxes and to assess the potential of the ORCHIDEE model. The overall objectives of this proposal are threefold: (1) Optimisation of all critical parameters of ORCHIDEE and assessment of the limits of this process-based model to simulate eddy covariance measurements. (2) Identification of drivers and processes determining inter annual variations of forest carbon fluxes. (3) Improved model future projections of Europe’s carbon balance, with uncertainty estimates, using the optimized parameters.'

Introduzione (Teaser)

European research has studied a terrestrial biosphere model to elucidate the mechanisms behind annual variations of carbon in European forest ecosystems.

Descrizione progetto (Article)

There are many ways in which the behaviour of an ecosystem can be measured. Healthy ecosystems have a predictable amount of a substance leaving and re-entering, sometimes building up certain substances like carbon as the system develops. Net ecosystem exchange (NEE) is the measurement used to determine how much carbon is entering and leaving the system.

Varying values of NEE between years driven by weather and climate are known to contribute to global carbon dioxide (CO2) levels but understanding of the underlying processes is scant. Knowledge on the varying responses of the biotic component (living part) to environmental forcing could help to more accurately predict future levels of CO2 globally.

The EU-funded Police project aimed to assess the effects of extreme climate spells as in 2003 compared with those of a 'normal' year on Europe's carbon balance. The summer of 2003 saw the highest temperatures on record throughout the continent.

The Police scientists optimised all critical parameters of Orchidee, the new land-surface scheme of the Laboratoire des sciences du climat et de l'environnement (IPSL). They assessed the limits of this process-based model to simulate eddy covariance measurements, an atmospheric measurement technique to calculate vertical turbulent fluxes within atmospheric boundary layers. It is commonly used to determine gas exchange rates of water vapour and CO2 for example.

Refining climate prediction models with data on climate changes and their impact can lead to a better understanding of the forces in play and a more accurate forecasting of parameters crucial to the Earth's changing climate.