Figure 4.3 shows the climatological cycle of precipitation across the domain for the NCEP and JapRe reanalysis datasets and the selected models for the climatology period. Despite the slight difference between the two observed cycles, it is still evident that the majority of models produce an annual cycle that moves too far north, with precipitation spread across a large part of the domain during most of the year, causing it to be overestimated in places. The models producing the most realistic annual cycles during this period are the MPI and MRI models.
5. Model derived crop growth thresholds Employing the same approach as used in Section 2, the domain masking exercise is repeated for the 8 models and the ensemble output. This allows for examination of the impact of model errors on simulated crop growth regions under current (1970–1999) climatic conditions. These plots are shown in Appendix 2, Figures B1 to B10 for both the model ensemble and each model. For reference, the climatic crop growth maps using both the NCEP and JapRe precipitation datasets are included for each crop. Banana: The ensemble output follows the climatological growth region well, although the optimum area in the ensemble is slightly smaller and does not extend into Uganda. The southern border of growth is further south in the ensemble due to the precipitation distribution biases in the models. The individual models exhibit greater variation in their representation of current banana growth regions though almost all manage to locate the optimal area for banana growth well. Cassava: Cassava is a crop that can be widely grown over East Africa and the model ensemble domain reflects this. One key difference is that the precipitation distribution in the models suggests that cassava can be grown over northern Kenya and eastern Ethiopia when observed precipitation makes these regions inappropriate for cassava cultivation. This is reflected in the individual models with the most realistic precipitation regimes Maize: The key optimal region of maize growth over central-southern Sudan is well replicated by the model ensemble as are other areas of varying suitability. As with cassava, the weakest element of the model simulation of the crop cultivation region is in eastern Ethiopia and northern Kenya where the models overestimate precipitation. However, half of
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