Full Text Available
Note: Clicking the button above will open the full text document at the original institutional repository in a new window.
A CMIP5 Model Selection Specific to South Africa's Winter Rainfall Zone
This study undertakes a CMIP5 model selection specific to the Winter Rainfall Zone (WRZ) of South Africa, seeking to reduce the range of future climate projections through identifying a subset of models with increased realism and independence. In order to navigate the subjectivity in identifying rel...
Saved in:
| Main Author: | |
|---|---|
| Other Authors: | |
| Format: | Thesis |
| Language: | English |
| Published: |
Department of Environmental and Geographical Science
2023
|
| Subjects: | |
| Tags: |
No Tags, Be the first to tag this record!
|
| _version_ | 1867614075248181248 |
|---|---|
| access_status_str | Open Access |
| author | Marsh, Peter |
| author2 | Jack, Christopher |
| author_browse | Jack, Christopher Marsh, Peter |
| author_facet | Jack, Christopher Marsh, Peter |
| author_sort | Marsh, Peter |
| collection | Thesis |
| description | This study undertakes a CMIP5 model selection specific to the Winter Rainfall Zone (WRZ) of South Africa, seeking to reduce the range of future climate projections through identifying a subset of models with increased realism and independence. In order to navigate the subjectivity in identifying relevant circulation metrics to assess models against, the ‘Day Zero' drought is used as a characteristic episode. Here initially the extensive literature produced subsequent to the drought has been drawn on to identify and evaluate relevant regional process metrics, before utilising the anomalous conditions during the drought to validate various assessment methods. The dynamics subsequently identified as being most influential to rainfall supply in the WRZ include the South Atlantic subtropical jet stream responsible for steering of mid-latitude storm systems, the South Atlantic subtropical high, and the presence, or preferably absence, of precipitation blocking subsidence, and the prevalence of mid-latitude storm systems, critical for transport and upliftment of moisture to the region. Models were subsequently assessed against these metrics and scored following the technique of McSweeney et al. (2015). Unrealistic models were removed from the ensemble while significantly biased models were also excluded as their absence did not significantly reduce the range of future projections. The same scoring methods were then utilised to create a genealogy of models attaining similar results to that of Knutti, Masson & Gettelman (2013). A subset of 6 CMIP5 models which are more independent and historically more realistic than that of the full ensemble were subsequently identified. While the range of future temperature projections of the final ensemble are somewhat constrained in comparison to the full ensemble, the primary utility is argued to be the reduced number of models where a future researcher may consider each model's projected future climate pathway individually before selecting a model, or models, which best informs their use case, whilst being assured that this model performs suitably well in the region and that the initial ensemble considered adequately represents model uncertainty, while strong similarity between two or more models within the ensemble will not be unduly biasing results. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/37614 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:46:16.523Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2023 |
| publishDateRange | 2023 |
| publishDateSort | 2023 |
| publisher | Department of Environmental and Geographical Science |
| publisherStr | Department of Environmental and Geographical Science |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/37614 A CMIP5 Model Selection Specific to South Africa's Winter Rainfall Zone Marsh, Peter Jack, Christopher Geographical Sciences This study undertakes a CMIP5 model selection specific to the Winter Rainfall Zone (WRZ) of South Africa, seeking to reduce the range of future climate projections through identifying a subset of models with increased realism and independence. In order to navigate the subjectivity in identifying relevant circulation metrics to assess models against, the ‘Day Zero' drought is used as a characteristic episode. Here initially the extensive literature produced subsequent to the drought has been drawn on to identify and evaluate relevant regional process metrics, before utilising the anomalous conditions during the drought to validate various assessment methods. The dynamics subsequently identified as being most influential to rainfall supply in the WRZ include the South Atlantic subtropical jet stream responsible for steering of mid-latitude storm systems, the South Atlantic subtropical high, and the presence, or preferably absence, of precipitation blocking subsidence, and the prevalence of mid-latitude storm systems, critical for transport and upliftment of moisture to the region. Models were subsequently assessed against these metrics and scored following the technique of McSweeney et al. (2015). Unrealistic models were removed from the ensemble while significantly biased models were also excluded as their absence did not significantly reduce the range of future projections. The same scoring methods were then utilised to create a genealogy of models attaining similar results to that of Knutti, Masson & Gettelman (2013). A subset of 6 CMIP5 models which are more independent and historically more realistic than that of the full ensemble were subsequently identified. While the range of future temperature projections of the final ensemble are somewhat constrained in comparison to the full ensemble, the primary utility is argued to be the reduced number of models where a future researcher may consider each model's projected future climate pathway individually before selecting a model, or models, which best informs their use case, whilst being assured that this model performs suitably well in the region and that the initial ensemble considered adequately represents model uncertainty, while strong similarity between two or more models within the ensemble will not be unduly biasing results. 2023-03-31T08:27:38Z 2023-03-31T08:27:38Z 2022 2023-03-29T08:51:52Z Master Thesis Masters MSc http://hdl.handle.net/11427/37614 eng application/pdf Department of Environmental and Geographical Science Faculty of Science |
| spellingShingle | Geographical Sciences Marsh, Peter A CMIP5 Model Selection Specific to South Africa's Winter Rainfall Zone |
| thesis_degree_str | Master's |
| title | A CMIP5 Model Selection Specific to South Africa's Winter Rainfall Zone |
| title_full | A CMIP5 Model Selection Specific to South Africa's Winter Rainfall Zone |
| title_fullStr | A CMIP5 Model Selection Specific to South Africa's Winter Rainfall Zone |
| title_full_unstemmed | A CMIP5 Model Selection Specific to South Africa's Winter Rainfall Zone |
| title_short | A CMIP5 Model Selection Specific to South Africa's Winter Rainfall Zone |
| title_sort | cmip5 model selection specific to south africa s winter rainfall zone |
| topic | Geographical Sciences |
| url | http://hdl.handle.net/11427/37614 |
| work_keys_str_mv | AT marshpeter acmip5modelselectionspecifictosouthafricaswinterrainfallzone AT marshpeter cmip5modelselectionspecifictosouthafricaswinterrainfallzone |