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Understanding how climate change affects the tropical rain belt over Africa and its variability

Dr John Marsham (SEE), Dr Dave Rowell (Met Office), Prof Doug Parker (SEE)

Project partner(s): UK Met Office

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The tropics cover 40% of Earth’s area, include 36% of its land, and are home to 40% of its people. Africa is the continent with the largest tropical land mass, and its rapidly growing population includes many of the people who are most vulnerable to climate change. Rainfall in the tropics is dominated by the tropical rain band (Figure 1) that encircles earth. To first order the rain-band moves to follow the solar heating, to reach its northernmost extent in the northern hemisphere summer, and its southernmost extent in northern hemisphere winter. As a result this movement, rainfall from the tropical rain-band directly affects not only the lush tropical forests of the Congo, but regions such as the southern reaches of the Sahara. The rain-band’s movement leads to the annual West African monsoon rains on which populations in the Sahel depend, and the bi-annual rains of East Africa, which vary enormously across the region from the highlands of Ethiopia to the deserts of Somalia. This PhD will use a range of state-of-the-art models and observations to understand how climate change affects the tropical rainbelt, with a focus on Africa, using and developing models of global change, together with regional models.

Rain ascends in the tropical rain band, causing clouds and rain, and descends further north or south, causing the great deserts of the world, including the Sahara (the “Hadley circulation”). There is a diverse response of this rain belt from anthropogenic climate change in idealised models, exemplified in Figure 2, but also seen in simulations of the real world (e.g. Dunning et al., 2018). Understanding these changes and the processes governing them is made much more challenging by the fact that the cumulonimbus storms that generate the rainfall and provide the ascent in the rain-band are sub-grid in global models, which have grid-spacings of approximately 100km, so must be represented by simplifications known as parametrisations. Recently the £20 million Future Climate for Africa (FCFA) programme has run the first simulations, referred to as “CP4A”, that have a small enough grid-spacing (approximately 4km) to explicitly capture these storms (Stratton et al., 2018). This fundamentally changes the representation of convection and rainfall, and so provides a unique opportunity for new understanding. This PhD will examine a range of observations and models, to generate new understanding of observed and modelled changes in the tropical rain band.

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Related undergraduate subjects:

  • Applied mathematics
  • Astronomy
  • Atmospheric science
  • Computer science
  • Computing
  • Earth system science
  • Engineering
  • Environmental science
  • Geography
  • Geophysical science
  • Geophysics
  • Geoscience
  • Hydrology
  • Meteorology
  • Natural sciences
  • Physical geography
  • Physical science
  • Physics
  • Statistics