Study of climate variability and change in the Republic of Djibouti: intense trends and events simulated by regional modeling

Started in september 2021

Funding: ‘campus France’ grant

Supervisors: Pierre Camberlin (université de Bourgogne), Benjamin Pohl (université de Bourgogne), Omar Assowe Dabar (CERD)

Defense the 30 january 2025

Abstract

Among extreme climatic phenomena, intense precipitation events are a major global concern due to their likely increase in a warming atmosphere. This challenge is particularly critical in arid regions, where rainfall is infrequent but often severe. The Republic of Djibouti, in particular, is characterized by an arid climate combined with high rainfall variability, which fosters sudden flash floods with devastating impacts on populations and infrastructure. These consequences highlight the urgency of better understanding and anticipating current and future climatic disruptions to develop effective adaptation strategies. The frequency of intense precipitation events evolves geographically depending on the mechanisms that drive them, but these mechanisms remain largely unknown in Djibouti and its surrounding region. The main objectives of this thesis are thus to better understand the physical drivers of intense precipitation in Djibouti and to project their future evolution in a warming climate. The initial chapters investigate the atmospheric mechanisms behind intense precipitation in Djibouti at both fine local and synoptic scales. By combining in situ observations and satellite-derived estimates, a typology of rainy days was developed based on the spatial distribution and intensity of precipitation. Using ERA5 reanalysis data, the synoptic conditions associated with each type of rainy day were analyzed on a seasonal basis. These analyses revealed a diversity of rain-generating systems. During March–May, precipitation is predominantly driven by complex interactions between tropical and extratropical air masses, while July–September and October–November are more directly influenced by tropical circulation patterns and moisture convergence. At the local scale, the WRF model successfully simulated the key meteorological features of an observed intense precipitation event. The final chapters of the thesis focus on future projections of intense precipitation in the Northeast Africa and Arabian region, with a specific emphasis on the Republic of Djibouti. A preliminary evaluation of CMIP6 models showed that those with higher spatial resolution, which perform well at the regional scale, also perform well for Djibouti. Projections from the 10 selected models reveal a north-south differentiation in future changes to total precipitation during the January–February (JF) and March–May (MAM) seasons, with decreases in northern Arabia and moderate increases elsewhere, although uncertainties remain high, particularly for MAM. Conversely, the July–September (JJAS) and October–November–December (OND) seasons exhibit more significant positive changes with lower inter-model uncertainty. These increases in average precipitation are accompanied by a rise in the intensity and frequency of intense rainfall events. In Djibouti City, post-corrected projections indicate that the frequency of intense rainfall events causing floods could increase by a factor of 3.6 by the end of the 21st century.

Keywords

heavy rainfall ; rain-bearing mechanisms ; climate modelling ; climate projections ; Djibouti ; North-East Africa and Arabia

Thesis advisory panel

Yves Tramblay, IRD Montpellier
Nathalie Philippon, CRC

Jury

Elsa Mohin, université Complutense de Madrid – reviewer
Benjamin Sultan, IRD, ESPACE-DEV – reviewer
Gil Mahe, IRD, université de Montpelier – examiner
Pierre Camberlin, université de Bourgogne – supervisor
Benjamin Pohl, université de Bourgogne – cosupervisor
Omar Assowe Dabar, CERD/ORREC – cosupervisor
Mohamed Osman Awaleh, CERD/IST – invited
Moussa Mahdi Ahmed, CERD/ORREC – invited

extrait:

lien_externe:

titre:

Étude de la variabilité et du changement climatique dans la République de Djibouti : tendances et événements intenses simulés par la modélisation régionale

date_de_debut_these:

septembre 2021

nom:

Mohamed Waberi

date_de_debut_these_numerique:

202109

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kc_raw_content:

Study of climate variability and change in the Republic of Djibouti: intense trends and events simulated by regional modeling

Started in september 2021

Funding: 'campus France' grant

Supervisors: Pierre Camberlin (université de Bourgogne), Benjamin Pohl (université de Bourgogne), Omar Assowe Dabar (CERD)

Defense the 30 january 2025

 

Abstract

Among extreme climatic phenomena, intense precipitation events are a major global concern due to their likely increase in a warming atmosphere. This challenge is particularly critical in arid regions, where rainfall is infrequent but often severe. The Republic of Djibouti, in particular, is characterized by an arid climate combined with high rainfall variability, which fosters sudden flash floods with devastating impacts on populations and infrastructure. These consequences highlight the urgency of better understanding and anticipating current and future climatic disruptions to develop effective adaptation strategies. The frequency of intense precipitation events evolves geographically depending on the mechanisms that drive them, but these mechanisms remain largely unknown in Djibouti and its surrounding region. The main objectives of this thesis are thus to better understand the physical drivers of intense precipitation in Djibouti and to project their future evolution in a warming climate. The initial chapters investigate the atmospheric mechanisms behind intense precipitation in Djibouti at both fine local and synoptic scales. By combining in situ observations and satellite-derived estimates, a typology of rainy days was developed based on the spatial distribution and intensity of precipitation. Using ERA5 reanalysis data, the synoptic conditions associated with each type of rainy day were analyzed on a seasonal basis. These analyses revealed a diversity of rain-generating systems. During March–May, precipitation is predominantly driven by complex interactions between tropical and extratropical air masses, while July–September and October–November are more directly influenced by tropical circulation patterns and moisture convergence. At the local scale, the WRF model successfully simulated the key meteorological features of an observed intense precipitation event. The final chapters of the thesis focus on future projections of intense precipitation in the Northeast Africa and Arabian region, with a specific emphasis on the Republic of Djibouti. A preliminary evaluation of CMIP6 models showed that those with higher spatial resolution, which perform well at the regional scale, also perform well for Djibouti. Projections from the 10 selected models reveal a north-south differentiation in future changes to total precipitation during the January–February (JF) and March–May (MAM) seasons, with decreases in northern Arabia and moderate increases elsewhere, although uncertainties remain high, particularly for MAM. Conversely, the July–September (JJAS) and October–November–December (OND) seasons exhibit more significant positive changes with lower inter-model uncertainty. These increases in average precipitation are accompanied by a rise in the intensity and frequency of intense rainfall events. In Djibouti City, post-corrected projections indicate that the frequency of intense rainfall events causing floods could increase by a factor of 3.6 by the end of the 21st century.

 

Keywords

heavy rainfall ; rain-bearing mechanisms ; climate modelling ; climate projections ; Djibouti ; North-East Africa and Arabia

 

Thesis advisory panel

Yves Tramblay, IRD Montpellier
Nathalie Philippon, CRC

 

Jury

Elsa Mohin, université Complutense de Madrid - reviewer
Benjamin Sultan, IRD, ESPACE-DEV - reviewer
Gil Mahe, IRD, université de Montpelier - examiner
Pierre Camberlin, université de Bourgogne - supervisor
Benjamin Pohl, université de Bourgogne - cosupervisor
Omar Assowe Dabar, CERD/ORREC - cosupervisor
Mohamed Osman Awaleh, CERD/IST - invited
Moussa Mahdi Ahmed, CERD/ORREC - invited