Including tropical croplands in a terrestrial biosphere model: application to West Africa

Studying the large-scale relationships between climate and agriculture

rises two different issues: the impact of climate on crops, and the potential

feedbacks to climate from croplands. Extending existing Dynamic Global

Vegetation Models to account accurately for croplands offers a relevant and

consistent framework to address this twofold issue.

By introducing into the terrestrial biosphere model ORCHIDEE (IPSL)

parametrisations from the crop model SARRAH (CIRAD) which is calibrated over

the west african region, we developed an original large-scale model for tropical crops,

ORCH-mil. It realistically simulates growth and yield of millet when compared

to the original crop model on an experimental station in Senegal. The model

is then applied over West Africa using a 36-year climate reanalysis dataset.

The model is tested against national yields from the FAO database. The

ability of the model to simulate the spatial and temporal variability of

millet yields is assessed, as well as its ability to model the observed

relationship between weather and yields. Effect of crop duration on the skill

of the model is examined. Effects of croplands on surface energy fluxes are also considered. Results underline the need for some further

development and validation of the model. In the frame of the AMMA project (African Monsoon Multidisciplinary Analysis), potential applications of the model

include seasonal predictions of tropical cereals yields, agricultural impacts of

climate change in West Africa, and impacts of agricultural land-use on the

land surface Water and Carbon budgets over West Africa.