Background Paper - The Status and Possible Evolution of Climate Projections in West Africa
Ross Blamey, Lisa Coop, Christopher Jack, et al.
This background technical report summarizes findings from an assessment of the status and possible evolution of climate projections for the West Africa region. It includes an overview of the strengths and limitations of such data for understanding climate change and future projections in the region. Additionally, it describes how climate modeling is a complicated task in West Africa. Many challenges intersect the limitations within models including availability of observed data, and the unique and complex climate dynamics of the region.
Differences in climate in West Africa include a wet coastal region and a drier Sahel located further north. The report references Giannini et al. (2008) in that the rainfall pattern changes in the Sahel region are “unparalleled globally, in magnitude, spatial extent and duration”. This is of importance due to the high number or major cities that depend on agriculture for livelihoods in the Sahel region. Temperature contrasts between land and ocean is a key driver of the spatial distribution of rainfall in the area, including a monsoon season during the spring months. Although other considerations affect the climate, it is difficult to predict future climate scenarios due to the complex nature of the interactions involved.
Excerpt from the report:
Even though the scientific community attempts to use climate models to provide robust and useful information to assist decision makers, their projections inherently include uncertainties, which stem from a number of different sources. These sources can be categorized as follows:
- Natural Variability: This is also known as “climate noise,” and refers to the internal variability of the climate system that occurs irrespective of changes in external forcing3
- Emission-Scenario Uncertainty: Also known as forcing uncertainty, this relates to the lack of knowledge of how future society will alter atmospheric emissions of greenhouse gases, which can be considered as an external factor influencing the climate system.
- Model-Response Uncertainty: This arises from the use of different models that produce diverse results despite being forced with the same external forcing. This can be broken down into imperfect understanding, where the small scale physical processes are not well understood (e.g., cloud radiative effects and precipitation processes) and also model inadequacies (e.g., representing fine scale processes through parameterizations).
- Initial Condition Uncertainty: This is due to sparse or incomplete observations in time and space, of the type which are needed to initialize the model. This uncertainty is more likely to present a challenge in the shorter time scales, like weather forecasting and decadal forecasting.
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