Building a field- and model-based climatology of local water and energy cycles in the cultivated Sahel – annual budgets and seasonality
Author:
Velluet C., Demarty J., Cappelaere B., Braud I.ORCID, Issoufou H. B.-A., Boulain N., Ramier D., Mainassara I., Charvet G., Boucher M., Chazarin J.-P., Oï M., Yahou H., Maidaji B., Arpin-Pont F., Benarrosh N., Mahamane A., Nazoumou Y., Favreau G.ORCID, Seghieri J.
Abstract
Abstract. In the African Sahel, energy and water cycling at the land surface is pivotal for regional climate, water resources and land productivity, yet it is still extremely poorly documented. As a step towards a comprehensive climatological description of surface fluxes in this area, this study provides estimates of average annual budgets and seasonal cycles for two main land use types of the cultivated Sahelian belt, rainfed millet crop and fallow bush. These estimates build on the combination of a 7 year field dataset from two typical plots in southwestern Niger with detailed physically-based soil-plant-atmosphere modelling, yielding a continuous, comprehensive set of water and energy flux and storage variables over the 7 year period. In this study case in particular, blending field data with mechanistic modelling is considered as making best use of available data and knowledge for such purpose. It extends observations by reconstructing missing data and extrapolating to unobserved variables or periods. Furthermore, model constraining with observations compromises between extraction of observational information content and integration of process understanding, hence accounting for data imprecision and departure from physical laws. Climatological averages of all water and energy variables, with associated sampling uncertainty, are derived at annual to subseasonal scales from the 7 year series produced. Similarities and differences in the two ecosystems behaviors are highlighted. Mean annual evapotranspiration is found to represent ~82–85% of rainfall for both systems, but with different soil evaporation/plant transpiration partitioning and different seasonal distribution. The remainder consists entirely of runoff for the fallow, whereas drainage and runoff stand in a 40–60% proportion for the millet field. These results should provide a robust reference for the surface energy- and water-related studies needed in this region. The model developed in this context has the potential for reliable simulations outside the reported conditions, including changing climate and land cover.
Publisher
Copernicus GmbH
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