East African population exposure to precipitation extremes under 1.5 °C and 2.0 °C warming levels based on CMIP6 models

Abstract

Understanding population exposure to precipitation-related extreme events is important for effective climate change adaptation and mitigation measures. We analyze extreme precipitation using indices (EPIs), including consecutive dry days (CDD), annual total precipitation, simple daily intensity, and the number of extremely wet days, under the past and future climatic conditions over East Africa. The exposure of the East African population to these extreme events at 1.5°C and 2.0°C global warming levels is analyzed based on Climate Model Intercomparison Project phase 6 (CMIP6) models. Exposure is computed from extremely wet and dry days (R95p and CDD, respectively). Under both global warming levels, EPIs (except CDD) averaged over East Africa are projected to increase under the Shared Socio-economic Pathways (SSP)2-4.5 and SSP5-8.5 scenarios. The largest increase in wet events will likely occur in eastern and northern Kenya. The results also reveal an intensification of precipitation extremes over Burundi, Rwanda, and some parts of Uganda. However, small changes are expected over most parts of Kenya and Tanzania. Examination of population exposure to EPIs shows that the most prominent and net intense occurrence is over Burundi, Rwanda, and some parts of Uganda. In contrast, less change is noted to occur over vast parts of Kenya and Tanzania. Meanwhile, limiting the warming target to less than 1.5 °C but not more than 2.0 °C has 37% (44.2%) and 92% (4%) less impact on the occurrence of EPIs for R95p (CDD) under SSP2-4.5 (SSP5-8.5) scenarios, respectively. The study establishes that future exposure is predominantly driven by changes in population compared to other factors such as climate or concurrent changes in climate and population (the nonlinear interaction effect). For instance, climate effects are anticipated to contribute ~10.6% (12.6%) of the total change in population exposure under 1.5 (2.0 oC) warming levels, while population and interaction effects are expected to contribute ~77.4% (71.9%) and 12% (15.5%), respectively, under 1.5 (2.0 ºC) scenarios. Interestingly, the projected changes in regional exposure due to the interaction effects under SSP2-4.5 are greater than the climate effect, while the reverse pattern is observed under SSP5-8.5. For example, under SSP5-8.5, climate effects for 1.5 ºC and 2.0 ºC are larger (after population effect) with ~3.8 × 105 (15.7%) and ~6.1 × 105 (17.5%) billion person-mm, respectively. The high exposure noted over East Africa calls for a shift in policies to instate suitable adaptation measures to cushion the already vulnerable population.

Projected Impact of Increased Global Warming on Heat Stress and Exposed Population Over Africa

“…Furthermore, the total change in exposure (in person‐events) will be investigated based on the approach developed by Jones et al. (2015) and adopted by certain authors (e.g., Ayugi et al., 2022; Liu et al., 2017; Weber et al., 2020), through the following equation: $$${\Delta }\boldsymbol{E}={\boldsymbol{P}}_{\boldsymbol{R}}\times {\Delta }\boldsymbol{C}+{\boldsymbol{C}}_{\boldsymbol{R}}\times {\Delta }\boldsymbol{P}+{\Delta }\boldsymbol{C}\times {\Delta }\boldsymbol{P}$$$ where $${\boldsymbol{P}}_{\boldsymbol{R}}$$ and $${\boldsymbol{C}}_{\boldsymbol{R}}$$ are the population and climate (the total number of occurrence of heat stress events) in the reference period, respectively; while $${\Delta }\boldsymbol{C}$$ and $${\Delta }\boldsymbol{P}$$ the climate and population changes, respectively. In Equation 2, the term $${\boldsymbol{P}}_{\boldsymbol{R}}\times {\Delta }\boldsymbol{C}$$ refers to the climate effect, which takes into account the influence of climate exposure; the term $${\boldsymbol{C}}_{\boldsymbol{R}}\times {\Delta }\boldsymbol{P}$$ represents the population effect; and the term $${\Delta }\boldsymbol{C}\times {\Delta }\boldsymbol{P}$$ refers to the interaction effect which measures the simultaneous variations in both climate and population.…”

“…In this study, exposure is defined as the size of population be exposed to heat stress, and is computed at each grid point by multiplying the total number of occurrences of these heat events and population together for both baseline and future periods. Furthermore, the total change in exposure (in person-events) will be investigated based on the approach developed by Jones et al (2015) and adopted by certain authors (e.g., Ayugi et al, 2022;Liu et al, 2017;Weber et al, 2020), through the following equation:…”

“…Alongside the above studies, which are focused on extreme heat events, some authors have looked at other extreme weather events combined with population change, which can also have severe consequences on the socio‐economic development of the affected countries (e.g., Ayugi et al., 2022; Bouwer, 2013; Weber et al., 2020; among authors). Although these studies have investigated the combination of climate and population change, most of them focused their attention just on certain subregions or countries of Africa (Asefi‐Najafabady et al., 2018; Fotso‐Nguemo et al., 2021; Iyakaremye et al., 2021; Jagarnath et al., 2020; Ma & Yuan, 2021; Sylla et al., 2018; Yengoh & Ardö, 2020).…”

Projected impact of increased global warming on heat stress and exposed population over Africa

“…In this study, exposure is defined as the size of population be exposed to heat stress, and is computed at each grid point by multiplying the annual number of occurrences of these heat events and population together for both baseline and future periods. Furthermore, the total change in exposure (in person-events) will be investigated based on the approach developed by Jones et al ( 2015) and adopted by certain authors (e.g., Liu et al, 2017;Weber et al, 2020;Ayugi et al, 2022), through the following equation:…”

“…Alongside the above studies, which are focused on extreme heat events, some authors have looked at other extreme wheather events combined with population change, which can also have severe consequences on the socio-economic development of the affected countries (e.g., Bouwer, 2013;Weber et al, 2020;Ayugi et al, 2022;among authers). Although these studies have investigated the combination of climate and population change, most of them focused their attention just on certain subregions or countries of Africa (Sylla et al, 2018;Asefi-Najafabady et al, 2018;Jagarnath et al, 2020;Yengoh & Ardö, 2020;Fotso-Nguemo et al, 2021).…”