Evidence of human-induced changes in rainfall across the world

Beena Balan Sarojini1,2, Peter Stott3, Emily Black1,2 and Debbie Polson4

1NCAS-Climate,2Walker Institute, Meteorology Dept., University of Reading, 3Met Office Hadley Centre, 4University of Edinburgh

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Beena Balan Sarojini is a Post-doctoral researcher funded jointly by NCAS-Climate and Met Office Hadley Centre.

What are the new findings?

Rainfall has increased over many parts of the world since 1950s. We demonstrate that humans are responsible for these changes by analysing state-of-the-art observations and climate model simulations. The most marked trends are seen at northern high latitudes for all seasons and northern subtropical oceans in winter (see figure on the right). In other parts of the world, we show that our ability to detect changes and determine their cause is hampered by the sparseness of observations. This is especially the case in the tropics.

Why are these findings important?

Our findings add weight to the evidence for manmade changes in rainfall and show that some regions of the world are affected more than others. Our comparison between simulated and observed rainfall has also highlighted gaps in the rainfall observing network, which may be obscuring rainfall trends in some regions. As well as improving our understanding of both simulated and observed rainfall trends, this study has the potential to inform climate change policy. Our results are contributing towards the evidence of climate change being assessed by the United Nation’s next IPCC (Intergovernmental Panel on Climate Change) report.

How did we discover this?

We used measurements of rainfall and computer simulations carried out by state-of-the-art climate models from fifteen leading climate centres around the world. The first step was to identify the trend caused by manmade factors, such as greenhouse gas emissions by comparing full model simulations, which included both manmade and natural factors, against simulations that included only natural factors. The next step was to investigate these trends in observations. Finally, we used the climate simulations to infer the effect that sparseness of rainfall measurements had on the observed trend. We did this by comparing the trends calculated when all points were included, with those calculated only for points at which there were observed data.

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Above: Year to year high latitude rainfall has gone up when climate models are driven by both natural factors and greenhouse gases (red) compared to when they are driven by natural factors only (blue). It has been possible to distinguish that the effect of human influence has been significant (green) since the 1990s. The measured rainfall is shown in black.

 

Find out more:

  • see Beena Balan Sarojini'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

Balan Sarojini et al. (2012), Geophysical Research Letters, doi: 10.1029/2012GL053373

 

 

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This research was funded by UK Natural Environment Research Council’s Changing Water Cycle Programme through the PAGODA project.