J3.4 Evaluation of GCM surface processes over West Africa using offline land surface models and observations (2008

J3.4

Evaluation of GCM surface processes over West Africa using offline land surface models and observations

Aaron A. Boone, CNRM, Toulouse, Midi-Pyrenees, France; and I. Poccard-Leclercq and Y. K. Xue

West Africa has been subjected to extreme climatic variability over

the last half century, notably a prolonged dry period

during the 70s-90s which had a significant impact on the people of

this region owing to the largely agrarian-based economies.

The African Multidisciplinary Monsoon Analysis (AMMA) project was

organized in recent years with the main goal of obtaining a

better understanding of the strong intra-seasonal and inter-annual

variability of the west-African monsoon (WAM). In particular,

land-atmosphere coupling is theorized to be of particular importance

in this region. The magnitude of the north-south gradient of surface

fluxes (modulated by soil moisture and vegetation) exerts a strong

influence on the position of the tropical front and possibly the

strength of the monsoon and the African Easterly Jet.

Several international model intercomparison projects are underway to

address these issues. One of the goals of the West African Monsoon

Modeling and Evaluation project (WAMME) is to use multiple GCMs and

regional climate models (RCMs) to examine the role of land-atmosphere

interaction, land-use and water-use change, and vegetation dynamics on

WAM development. In parallel, the AMMA Land surface Model

Intercomparison Project (ALMIP) consists in forcing an ensemble of

state-of-the-art land surface models with the best quality (combining

numerical weather prediction, satellite and ground-based observations)

data available in order to better understand the key surface

processes. The ALMIP land surface states then represent an

analogue to a land surface re-analysis product.

Therefore in this

talk, data from the ALMIP project will be used to

evaluate the ability of the fully coupled WAMME-GCMs to simulate the

land surface state. There will be a focus on those quantities which

have strong links with remotely sensed and

surface network data data,

such as the GCM predicted precipitation and surface net radiative

fluxes. Observational data from recent observational campaigns,

such as soil moisture, will be used to

evaluate the simulated values along a heavily instrumented

north-south transect.

In offline mode, analysis of the ALMIP results revealed that the

partitioning of the evaporation components and runoff were particularly

variable among the models, and these processes will be inter-compared

with the fully coupled model results.