Improving predictions of long-term African Sahel rainfall

 

Michael Vellinga1, Malcolm Roberts1, Pier Luigi Vidale2, Matthew S. Mizielinski1, Marie-Estelle Demory2, Reinhard Schiemann2, Jane Strachan1, Caroline Bain1

1 Met Office Hadley Centre, Exeter, UK, 2 NCAS Climate, University of Reading, UK

 

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Dr Demory is a senior research scientist. Her research focuses on high-resolution climate modelling and the hydrological cycle.

What are the new findings?

The Sahel is prone to substantial fluctuations in summer rainfall. Prolonged, multi-year droughts have occurred in the 20th century, causing devastating losses to society. Simulating these fluctuations has remained problematic for climate models for many years because the models did not have sufficient resolution (number of pixels) to capture the magnitude of these fluctuations and understand their cause. Here we show that most of these rainfall fluctuations are caused by changes in large clusters (100s of km) of heavy rainfall. Such rainfall events are only captured by global climate models using very high resolution (very refined pixels) of 25 to 12 km.

Why are these findings important?

Ability to produce intense, large clusters of rainfall allows climate models to correctly simulate the magnitude of late-twentieth century rainfall change over the Sahel, underlining the importance of model resolution. These results provide a strong basis for developing more reliable and accurate long-term predictions of rainfall (seasons to years) that could benefit many sectors in the region (such as water, energy, insurance industries, farmers, people), by allowing early adaptation to impending extremes.

How did we discover this?

We analysed rainfall of the 20th century from observations and compared it with rainfall simulated by global climate models of different horizontal resolutions (pixel sizes) of 135, 60, 25, 12 km. Only the 25 and 12 km models produced realistic heavy rainfall events and their multi-annual changes that underpin Sahel drought.

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Above:Two contrasting model views of Sahel rainfall and clouds. Snapshots of cloud (grey shading; cloud-free areas are black) and intense rainfall (>1.5 mm/hour; purple) in the 135 km (top) and 12 km models (bottom)

Find out more:

  • Read more
  • see Marie-Estelle Demory's webpage
  • Email: This email address is being protected from spambots. You need JavaScript enabled to view it.
  • Take a look at the Journal article

Vellinga, M. et al (2016), Geophysical Research Letters, 43, 326–333

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This research was funded by the Met Office, DFID, DECC, DEFRA, NCAS, JWCRP and PRACE.