Context and Objectives
The continental biosphere is a key component in the climate system. It controls the partitioning of available radiative energy at the surface between sensible and latent heat (i.e. turbulent exchanges of dry heat and moisture), and it controls the partitioning of rainfall between evaporation and runoff. The continental biosphere is also an essential component in the global carbon cycle since it has absorbed large amounts of the fossil fuel CO2 emissions and therefore acted as a carbon sink since the pre-industrial era.
Moreover, there are increasing evidences that the influence of the land surface is significant on climate and that changes in its characteristics (e.g. deforestation, grazing, irrigation, urban planning, ...) can influence regional- to global-scale climate on time scales from days to millennia. Further, there is now a suggestion that the terrestrial carbon sink may decrease as global temperatures increase (as a consequence of rising CO2 level), thereby leaving more of the anthropogenically emitted CO2 in the atmosphere and increasing the magnitude of global warming.
This course introduces the fundamental exchanges that take place at the interface between the terrestrial biosphere and the atmosphere. It will show why terrestrial biosphere can influence the composition and circulation of the overlying air masses. Meteorology and climate therefore not only impact the functioning of the land-surfaces, but are also impacted by them. There is a real interaction between them. Our capabilities to properly model those interactions are crucial in projections of future local-regional and potentially global climate changes, and to design adequate land-use adaptation strategies.

Implementation

The course will be divided in two major parts:
• a more academic part to start with, that will introduce the fundamental exchanges that take place at the land-atmosphere interface,
• a more research-driven part that will make the best use of the science in progress to illustrate what we know, what the unknowns are, what and where the uncertainties are, and what remains to be done.

Fundamental Exchanges at the land-atmosphere Interface. Theory and modelling.
1- Radiative energy budget
* classical approach (reminder - fundamentals)
* Radiation within the canopy
2- Energy budget
* Energy balance equation, convective transfer of heat and mass (reminder - fundamentals)
* Evapotranspiration
> Theoretical approach (Potential evaporation and then transpiration)
> Practical approach (ET0 – Penman and Kc)
3- Turbulent transfer at the air-vegetation interface
* Properties of the underlying surface (momentum fluxes, roughness, zero-plane displacement, aerodynamical resistance) - (reminder - fundamentals)
* Specifics of the near-surface turbulence (profiles in plant canopies, boundary layer in the cover,
4- Resistive scheme for the exchange between soil-vegetation-atmosphere continuum
* Stomatal resistance and regulation (fundamentals)
* Compensation points for the gaseous exchanges

5- Water and carbon circulation and storage in plants and ecosystems
* Water circulation in plants
* Plant growth; use and impacts of CO2
* Soil-plant (ecosystem?) feedbacks with the atmosphere

6- Resume of our understanding: Biosphere-Atmosphere interactions, application for the pollutant exchanges.
* Greenhouse gas
* Pollutants implicated in the air quality

Evaluating models of the terrestrial Biosphere
Experimental methods for estimating the fluxes of Energy and Matter
* Profile Method
* Eddy Covariance Method
* Accumulation Methods
* Teledetection

Identification of atmospheric impacts of the terrestrial Biosphere
1. What evidences do we have that land-uses (change in the distribution of vegetation, wetland drainage, irrigation, urban expansion, …) do impact on the mean climate, on its spatial and temporal variability, and on extreme meteorological events (droughts, floods, …)?
2. Can the terrestrial biosphere be used as a mean to mitigate climate change?

Dernière mise à jour : mercredi 20 avril 2011