Have you ever seen the rain?

The 20th session of the Conference of the Parties and the 10th session of the Conference of the Parties serving as the Meeting of the Parties to the Kyoto Protocol is held from 1 to 12 December. For COP 20 / CPM 10 delegates from around the world increased their carbon footprint by heading to Lima, Peru, to hopefully produce more than just hot air. So again it is time to speak about the weather…or climate.

Animation of a gridded cartogram projection of global annual precipitation patterns
(click for larger version)

This animation is a visualisation which I originally produced for my PhD research and which was published in my book Rediscovering the World. While the printed book showed these maps in static form, the above animation gives a much more vivid impression of the current climate observations on the global precipitation distribution over a period of approximately 50 years (~1950-2000, obtained from the WorldClim database).
Compared to the complex models and research of climate scientists, a gridded cartogram transformation of their data appears quite insignificant and small. From a cartographic perspective, the efforts are of course a little bit more considerable and (still) less straight forward. The above animation shows a gridded cartogram transformation that displays the distribution of the total precipitation in an areas as a map base and includes a topographic display (with green being the lowest lying regions) as well as the graticule for further guidance. As cartograms are still very much being seen as more useful in the social sciences this is one of the very few cartogram visualisations of environmental data, showing how also environmental data can benefit from alternative forms of cartographic displays when using approaches that take the complexity and detail of their underlying data into account.
This dynamic impression of the changing nature of precipitation patterns reveals the seasonal changes in a high geographic detail. Monsoon rain in Asia, seasonal variation around the Equator, winter rain in the Mediterranean climates and other ‘text-book’ patterns are shown in their full quantitative extent without losing their geographical reference. The meandering lines of latitude in the map are the expression of these changing patterns in the shape of precipitation distribution. The animation of this map series adds further visual appeal to the cartogram and allows for a more direct comparison of the changing patterns in this appearance of a map in motion.
Putting all months together to an annual precipitation cartogram results in the following image which shows the totals for a full year (from these long-term observations):

Gridded cartogram projection of global annual precipitation patterns
(click for larger version)

Here the full quantities of rainfall (and other precipitation) patterns are made visible. The cartogram shows the high rainfall volumes in the tropical regions north and south of the equator. Areas of high seasonal precipitation volumes, such as the monsoon regions in Asia are less significant as they appear in the monthly map series before, but still strike out from the dry regions. Similarly, the areas where more even or more moderate precipitation levels (which covers also snowfall in the higher and colder climate regions) are prevalent, such as in Europe and parts of North America. The visualisation of the topography demonstrates the effects of mountain ranges as barriers where clouds lose their moisture while ascending.

How much are these pattern changing with humankind’s impact on the global climate? And how much of the change will we be able to influence for the benefit of future generations?
To be continued…

Find out more about the technique and the background on these maps in my book which is available from Springer
(buy at Amazon or as an iTunes iBook):

  • Hennig, Benjamin D (2013). Rediscovering the World: Map Transformations of Human and Physical Space. Heidelberg / New York / Dordrecht / London (Springer).
    doi: 10.1007/978-3-642-34848-8

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