Wet regions getting wetter, dry regions drier as planet warms


Chunlei Liu and Richard P.  Allan

Dept of Meteorology/NCAS-Climate, University of Reading

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Richard Allan is a lecturer at the Department of Meteorology in the University of Reading. He works on the global water cycle and how this may change in the future.


What are the new findings?

Observations and detailed computer simulations of the climate show reductions in rainfall over the drier tropical land regions (including parts of Africa and Australia) over the 20th century (see diagram). However, natural climate variability linked to El Niño explains large year to year fluctuations in tropical rainfall and also discrepancies between simulations and measurements. Simulations of the future indicate that drying of the drier regions continues (right) while wet regions will experience more rainfall as the world warms in response to rising greenhouse gas concentrations.

Why are these findings important?

Changes in the availability of fresh water can strongly impact societies and the ecosystems upon which they depend. These findings indicate that the heaviest rainfall is likely to become heavier which could cause more damage to infrastructure from flooding for example. Drying of already dry regions means that droughts may become more intense in the future.

How did we discover this?

We analysed over 30 climate change experiments using 13 state of the art climate simulators which were built by hundreds of scientists over many years. We split up the world's land and ocean into the wettest regions (heaviest rainfall) and the remaining drier regions (least rainfall). We compared the simulated changes in rainfall with measurements from rain gauges and satellites. There was a clear tendency for the wet regions to become wetter and the dry regions drier during the 21st century in response to global warming.


Above: Computer simulations (grey shading shows the range and black line shows the average of all simulations) and observations (blue and red lines) show declining rainfall over the driest tropical land regions.

Find out more:

  • see Richard Allan'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

Liu & Allan (2013) Environmental Research Letters, 8, 034002, doi:10.1088/1748-9326/8/3/034002
Allan et al. (2013) Surveys in Geophysics, doi:10.1007/s10712-012-9213-z


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This research was funded by UK Natural Environment Research Council’s PAGODA and PREPARE projects.