Abstract
Ethiopia and South Sudan contain several population centers and important ecosystems that depend on July–August rainfall. Here we use two models to understand current and future rainfall: the first ever pan-African numerical model of climate change with explicit convection and a parameterized model that resembles a typical regional climate model at 4.5 and 25 km horizontal grid-spacing, respectively. The explicit convection and higher resolution of the first model offer a greatly improved representation of both the frequency and intensity of rainfall, when compared to the parametrized convection model. Furthermore, only this model has success in capturing the east–west propagation of rainfall over the full diurnal cycle. Enhanced low-level westerlies were found for extremely wet days, though this response was weaker in the explicit convection model. The increased orographic detail in the explicit model resulted in the splitting of the low-level Turkana Jet core into smaller cores, and inhibited its penetration far into South Sudan. Some projected changes were found to be independent of model, such as changes in the strength of Somali and Turkana jets, as well as the shifting of Turkana jet core to lower levels. However, the explicit model end-of-century projections showed a larger and clearer decrease in wet days, accompanied by an increase in wet day intensity and extreme rainfall. This study highlights serious limitations of relying solely on simulations which parameterize convection to inform decisions in the region of South Sudan and Ethiopia.
Highlights
The Greater Horn of Africa is a region characterized by frequent extremes that have over the years caused great loss of life and impacted negatively on the economy of the region
Kendon et al [40] took a pan Africa perspective, and Finney et al [37] focused on the bimodal rainfall region of East Africa, whilst here we focus on Ethiopia and South Sudan, in the boreal summer, where moisture is supplied by the westerly West
Such effects cannot be quantified with this dataset; the majority of results discussed in this study are consistent with past convection-permitting studies of different regions, and current understandings of problems with existing parameterizations of moist convection [28,43], and can more reliably be attributed to the use of explicit convection
Summary
The Greater Horn of Africa is a region characterized by frequent extremes that have over the years caused great loss of life and impacted negatively on the economy of the region. Noting the added value in using high resolution data in this region, we utilized the first decade-long, convection-permitting climate change simulations for the Africa domain to investigate the relationship between circulation systems and extreme rainfall in the region, as well as provide the first focus on the region with this state-of-the-art dataset These datasets present an unprecedented opportunity to investigate the potential effects of climate change on the regions of South Sudan and Ethiopia. Convection-permitting models still have challenges in representing small-scale convective features and convection over the ocean [34], they have been shown to greatly improve representation of larger storms when compared to parametrized convection models [26] and they have often been shown to give larger climate changes in extreme rainfall This has recently been demonstrated for Africa [35,36,37,38,39] and so these high-resolution models are invaluable tools for understanding the characteristics of the current African climate and how this may change under global warming. Africa Monsoon (WAM) winds, but with additional influences from easterlies from the Indian Ocean
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