Climate change is a current, urgent and global issue. It is characterized by rising temper atures and highly variable precipitation, resulting in more frequent and intense extreme weather events, causing increased risks for affected urban areas. Despite its limited con tribution to global greenhouse gas emissions, Africa is disproportionately affected by cli mate change, as existing climate variability, socioeconomic fragility, and rapid population growth amplify its vulnerability. The objective of this thesis is to assess how climate risk, linked to rising temperatures and drought conditions, evolves over time in Africa’s fifteen most populous cities. This study integrates climate projections, downscaling techniques and risk assessment based on the interaction of climatic hazard, exposure and vulnerability. To this end, historical and future data referring to different time frames and emission scenarios are used to assess the evolution of risk under climate change. The methodological process begins with the selection of a historical climate dataset ca pable of accurately representing observed conditions at the local scale. Several datasets were compared, including observations from meteorological stations, CHIRPS/CHIRTS satellite products and the ERA5-Land reanalysis, with the aim of identifying the most reliable reference for the analysis. Once the historical dataset was selected, an empirical statistical downscaling approach based on the quantile mapping technique was applied to correct the outputs of global climate models. This procedure corrects systematic biases present in model simulations and ensures statistical consistency between projected and observed climate variables. Future climate conditions were analyzed by considering three future scenarios, represented by the Shared Socioeconomic Pathways (SSP1-2.6, SSP3-7.0, and SSP5-8.5), which rep resent different trajectories of socioeconomic development and greenhouse gas emissions. The climate data obtained from the downscaling process were used to calculate climate risk indicators, linked to heatwaves and drought conditions. These hazard metrics were then integrated with exposure and vulnerability components to estimate the risk for each city. Exposure was represented by population data, reflecting the rapid population growth expected in African urban areas, while vulnerability was calculated using a composite in dex derived from socioeconomic indicators at the national scale. The results indicate that temperature-related climate risks follow a clear increasing trend across different scenarios and time horizons, while precipitation-related risks exhibit greater spatial variability and uncertainty. At the same time, the sharp increase in urban popu lations significantly amplifies future exposure, contributing to an overall increase in risk levels in many cities. The analysis also highlights marked spatial differences within the continent, reflecting the influence of regional climate characteristics, urban growth pat terns, and socioeconomic conditions. Overall, this study demonstrates that climate risk in African urban areas is a multi-driver phenomenon that cannot be explained solely by climate factors. Instead, it arises from the interaction between physical hazards and socioeconomic dynamics. The findings highlight the importance of integrating climate projections with demographic and vulnerability data to better understand future risk trajectories and support the planning of adaptation strategies in rapidly growing cities.
Il cambiamento climatico è una questione attuale, urgente e globale. È caratterizzato dall’aumento delle temperature e da precipitazioni altamente variabili, che portano a eventi meteorologici estremi più frequenti e intensi, causando rischi crescenti per le aree urbane interessate. Nonostante il suo contributo limitato alle emissioni globali di gas serra, l’Africa è colpita in modo sproporzionato dal cambiamento climatico, poiché la variabil ità climatica esistente, la fragilità socioeconomica e la rapida crescita della popolazione amplificano la sua vulnerabilità. L’obiettivo di questa tesi è valutare come il rischio climatico, legato all’aumento delle temperature e alle condizioni di siccità, evolva nel tempo nelle quindici città più popolose dell’Africa. Questo studio integra proiezioni climatiche, tecniche di downscaling e valu tazione del rischio basata sull’interazione tra pericolo climatico, esposizione e vulnerabil ità. A tal fine, vengono utilizzati dati storici e futuri riferiti a diversi intervalli temporali e scenari di emissione per valutare l’evoluzione del rischio in un contesto di cambiamento climatico. Il processo metodologico inizia con la selezione di un dataset climatico storico in grado di rappresentare accuratamente le condizioni osservate a scala locale. Sono stati confrontati diversi dataset, tra cui osservazioni provenienti da stazioni meteorologiche, prodotti satel litari CHIRPS/CHIRTS e la rianalisi ERA5-Land, con l’obiettivo di identificare il riferi mento più affidabile per l’analisi. Una volta selezionato il dataset storico, è stato applicato un approccio empirico di downscaling statistico basato sulla tecnica del mapping quantile per correggere i risultati dei modelli climatici globali. Questa procedura corregge i bias sistematici presenti nelle simulazioni dei modelli e garantisce la coerenza statistica tra le variabili climatiche proiettate e quelle osservate. Le condizioni climatiche future sono state analizzate considerando tre scenari futuri, rap presentati dai Shared Socioeconomic Pathways (SSP1-2.6, SSP3-7.0 e SSP5-8.5), che rap presentano diverse traiettorie di sviluppo socioeconomico e di emissioni di gas serra. I dati climatici ottenuti dal processo di downscaling sono stati utilizzati per calcolare indicatori di rischio climatico, legati a ondate di calore e condizioni di siccità. Queste metriche di pericolo sono state poi integrate con componenti di esposizione e vulnerabilità per stimare il rischio per ogni città. L’esposizione è stata rappresentata dai dati sulla popolazione, riflettendo la rapida crescita demografica prevista nelle aree urbane africane, mentre la vulnerabilità è stata calcolata utilizzando un indice composito derivato da indicatori so cioeconomici a livello nazionale. I risultati indicano che i rischi climatici legati alla temperatura seguono una chiara ten denza crescente attraverso diversi scenari e orizzonti temporali, mentre i rischi legati alle precipitazioni mostrano una maggiore variabilità spaziale e incertezza. Allo stesso tempo, il forte aumento delle popolazioni urbane amplifica significativamente l’esposizione futura, contribuendo a un aumento complessivo dei livelli di rischio in molte città. L’analisi evi denzia anche marcate differenze spaziali all’interno del continente, riflettendo l’influenza delle caratteristiche climatiche regionali, dei modelli di crescita urbana e delle condizioni socioeconomiche. In generale, questo studio dimostra che il rischio climatico nelle aree urbane africane è un fenomeno causato da molteplici fattori che non può essere spiegato esclusivamente dai fattori climatici. Piuttosto, esso deriva dall’interazione tra pericoli fisici e dinamiche socioeconomiche. I risultati evidenziano l’importanza di integrare le proiezioni climatiche con i dati demografici e di vulnerabilità per comprendere meglio le traiettorie future del rischio e supportare la pianificazione di strategie di adattamento nelle città in rapida crescita.
Assessing the evolution of extremes temperature and drought risks in african cities
Carra, Giulia
2024/2025
Abstract
Climate change is a current, urgent and global issue. It is characterized by rising temper atures and highly variable precipitation, resulting in more frequent and intense extreme weather events, causing increased risks for affected urban areas. Despite its limited con tribution to global greenhouse gas emissions, Africa is disproportionately affected by cli mate change, as existing climate variability, socioeconomic fragility, and rapid population growth amplify its vulnerability. The objective of this thesis is to assess how climate risk, linked to rising temperatures and drought conditions, evolves over time in Africa’s fifteen most populous cities. This study integrates climate projections, downscaling techniques and risk assessment based on the interaction of climatic hazard, exposure and vulnerability. To this end, historical and future data referring to different time frames and emission scenarios are used to assess the evolution of risk under climate change. The methodological process begins with the selection of a historical climate dataset ca pable of accurately representing observed conditions at the local scale. Several datasets were compared, including observations from meteorological stations, CHIRPS/CHIRTS satellite products and the ERA5-Land reanalysis, with the aim of identifying the most reliable reference for the analysis. Once the historical dataset was selected, an empirical statistical downscaling approach based on the quantile mapping technique was applied to correct the outputs of global climate models. This procedure corrects systematic biases present in model simulations and ensures statistical consistency between projected and observed climate variables. Future climate conditions were analyzed by considering three future scenarios, represented by the Shared Socioeconomic Pathways (SSP1-2.6, SSP3-7.0, and SSP5-8.5), which rep resent different trajectories of socioeconomic development and greenhouse gas emissions. The climate data obtained from the downscaling process were used to calculate climate risk indicators, linked to heatwaves and drought conditions. These hazard metrics were then integrated with exposure and vulnerability components to estimate the risk for each city. Exposure was represented by population data, reflecting the rapid population growth expected in African urban areas, while vulnerability was calculated using a composite in dex derived from socioeconomic indicators at the national scale. The results indicate that temperature-related climate risks follow a clear increasing trend across different scenarios and time horizons, while precipitation-related risks exhibit greater spatial variability and uncertainty. At the same time, the sharp increase in urban popu lations significantly amplifies future exposure, contributing to an overall increase in risk levels in many cities. The analysis also highlights marked spatial differences within the continent, reflecting the influence of regional climate characteristics, urban growth pat terns, and socioeconomic conditions. Overall, this study demonstrates that climate risk in African urban areas is a multi-driver phenomenon that cannot be explained solely by climate factors. Instead, it arises from the interaction between physical hazards and socioeconomic dynamics. The findings highlight the importance of integrating climate projections with demographic and vulnerability data to better understand future risk trajectories and support the planning of adaptation strategies in rapidly growing cities.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/252938