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High impact weather in Africa under climate change

Dr John Marsham (SEE), Dr Cathryn Birch (SEE)

Contact email: J.Marsham@leeds.ac.uk

Although global anthropogenic climate change is well established, there is an urgent need for new science to understand the consequences of this for regional changes in high impact weather (e.g. reflected in the “Grand Challenges” of the World Meteorological Organisation). It is this weather that will create the impacts of climate change, whether that is droughts affecting food production, heavy rain causing floods, variable monsoon onsets, or changes to winds and rain causing desertification and dust storms. This is particularly true for Africa, where the population is already vulnerable to climate variability, and this will increase with population growth and climate change. This PhD will address this exciting challenge to better understand possible changes in high impact weather in Africa, combining newly available world-leading simulations with observations, theory and possibly new model runs.

Understanding changes in high impact weather requires a model that can capture the relevant forcings, responses and feedbacks. Global climate models have serious limitations in this regard, since their grid-spacing is too coarse to capture the rain-generating moist convection, and as a result they often fail to capture: the organised storms that dominate African weather; the links between locally forced circulations and storms; the positive or negative feedbacks that can occur between the land surface and the storms; changes in extremes (Kendon et al., 2014; Taylor et al., 2012; Birch et al., 2014). These failures have impacts on the continental scale and feature such as monsoons (Marsham et al., 2013). Within the Future Climate for Africa programme the Met Office is now running simulations of ten years of past and ten years of future climate for the whole of Africa at an unprecedented 4.5 km grid-spacing that for the first time allows explicit modelling of these couplings and feedbacks, providing a complete step-change in model capability. These runs are revolutionary and will provide a truly unique opportunity for this PhD to use to understand changing extremes and high impact weather.

Left: The domain of the world-leading CP4A simulations run at 4.5 km for 10 years in past and 10 years in future – previously we have only had roughly a quarter of this domain, for 100 days of past climate (image credit: Met Office). Right: Organised deep convective storms dominate African weather. These are sub-grid in climate models, but explicitly modelled in CP4A, providing new opportunities to understand future changes in such systems (image credit: NASA).

Objectives

The precise focus of the work depends on the interests of the student and the outcomes of the ongoing FCFA programme, although past experience shows that this programme is likely to only scratch the surface of the understanding that can be gained from the ground-breaking new runs. Likely objectives are outlined below.

  • Initially focusing on East or West Africa, where the supervisors have a wide experience of the relevant meteorology, quantify how the representation of convection controls a selected aspect of high impact weather, e.g. droughts, monsoon onset, floods or dust storms.
  • Understand the processes and feedbacks whereby a changed representation of moist convection affects the impact of climate change on the high impact weather.
  • Either focus this work down to understand the changes in a particular sub-region of interest (e.g. the Lake Victoria Basin, the highly populated coast of West Africa etc.) or expand this work to other regions, or address other forms of high impact weather.

Key to any research will be bringing new physical understanding to the changes seen in the simulations, using theory, observations and possibly other models, to disentangle mechanisms and feedbacks.

Training, Supervision and the Research Environment

You will join a very successful team of scientists at Leeds, with a broad track record of high-profile research on African weather and climate. You will work under the supervision of Dr John Marsham who has published 79 papers in 12 years, and has recently been promoted to Associate Professor. He manages a large group working across moist atmospheric convection and associated fields, and his past PhD students have strong records of peer-reviewed publication. Co-supervisor Cathryn Birch (Met Office senior scientist) is an expert with the Met Office Unified Model and on tropical meteorology.

The Leeds group is involved in 4 of the 5 projects within the Future Climate for Africa (FCFA) Programme, leading major components, and John Marsham leads the consortium addressing East Africa (HyCRISTAL). FCFA ends in July 2019, and the large SWIFT project on African weather forecasting (led from Leeds) is just starting, so you will be joining a strong and dynamic team, with numerous opportunities to learn from postdocs & students working in closely related fields, as well as from supervisors.

SEE and ICAS provides a large and diverse environment for research and you will be encouraged to travel to share your findings and learn from other environments. ICAS has formal partnerships with the Met Office and the Karlsruhe Institute of Technology (KIT, Germany), facilitating visits there, but there are also opportunities further afield, e.g. USA and Australia. Projects such as FCFA & SWIFT provide opportunities to engage with researchers and practitioners in Africa, and Leeds is often involved in major international field campaigns, which would require further travel.

Environmental and atmospheric modelling is growing field and the PhD will provide hands on experience with a world leading model, and access to appropriate training, for handling the data, for running models and in wider skills (http://www.emeskillstraining.leeds.ac.uk/).

Student profile

You will have a degree in a mathematical or physical science, and have some, but perhaps limited, familiarity with scientific programming, as the project will involve writing computer codes for data analysis. You will be interested in weather and climate, and the interface between them. A background in meteorology is useful but not essential -  excellent lecture courses in this are available at Leeds.

References

Birch, C. E., J. H. Marsham, D. J. Parker, C. M. Taylor (2014), The scale-dependence and structure of convergence fields preceding the initiation of deep convection, Geophys. Res. Lett., doi: 10.1002/2014GL060493.

Kendon, E.J., N. M. Roberts, H. J. Fowler, M. J. Roberts, S. C. Chan and C. A. Senior (2014), Heavier summer downpours with climate change revealed by weather forecast resolution model, Nature Climate Change, 4, 570-576, DOI: 10.1038/NCLIMATE2258.

Marsham, J. H., N. Dixon, L. Garcia-Carreras, G. M. S. Lister, D. J. Parker, P. Knippertz, C. E. Birch, 2013: The role of moist convection in the West African monsoon syst4, 570-em - insights from continental-scale convection-permitting simulations, Geophys. Res. Lett., 40, 1843-1849, doi:10.1002/grl.50347.

Taylor, C.M., R.A.M. de Jeu, F. Gucihard, P.P. Harris, W.A. Dori (2012) Afternoon rains more likely over drier soils, Nature, 489, 423-426, doi:10.1038/nature11377.

Future Climate for Africa programme

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