Projections of Human Exposure to Deadly Heat in African Cities Under Multiple Climatic and Socioeconomic Scenarios: powerpoint

In this presentation, we report the findings of a new study in which we combined projections of urban population under the five Shared Socioeconomic Pathways (SSPs) with projections of apparent temperature under three Representative Concentration Pathways (RCPs) in order to explore future exposure to deadly heat across 173 large African cities. Based on the multiple combinations of SSP and RCP, we show that the aggregate exposure in African cities will increase by a multiple of 20-52, reaching 86-217 billion person-days per year by the 2090s, depending on the scenarios combination. We also explore the individual influence of demographic and climatic changes on future exposure by computing the so-called climate effect, population effect, and interaction effect. Results show that at the continental level, exposure to deadly heat is primarily driven by the population and interaction effects, with the climate effect alone being negligible in all cases. Finally, and most importantly, we employ the SSP/RCP framework to assess the extent to which exposure can be avoided as a result of shifts in socioeconomic or climatic pathways. We particularly focus on comparing the avoided exposure due to shifts from a high (or medium) to a low urban population growth pathway with the avoided exposure due to shifts from a high (or medium) to a low radiative forcing pathway. Unlike the few existing studies that performed a similar analysis – but with different case studies –, we find that a shift from a high to a low urban population growth pathway leads to a slightly greater reduction in exposure than a shift from a high to a low emission pathway. In other words, comprehensive socioeconomic and urban growth policies that would trigger the transition from a highly populous and urbanized world (SSP4) to a less populous and highly equitable world (SSP1) may have a slightly greater influence on reduction in exposure to deadly heat than very ambitious mitigation that would contain the global radiative forcing as low as RCP2.6 (instead of RCP8.5). The degree to which this holds true, however, depends on the region considered. While the influence of socioeconomic pathways is reinforced in Western African cities – where the range of outcomes in future urban population size is much wider than the range of outcomes in deadly heat conditions (which are already high in the historical period) –, it is of minimal influence in Southern African cities where urban population growth is rather limited under all scenarios. Overall, findings of this study (1) stress the crucial role that urban population growth – and societal pathways more broadly – play in shaping future exposure to deadly heat in most African cities, and (2) highlight how the SSP/RCP framework can be employed to facilitate climate impact analyses and to disentangle the individual influence of changes in socioeconomic and climatic conditions