Where does it always rain on us?

Map Animation / Gridded Population Cartogram of Rainfall (Precipitation) patterns in relation to people

Does it never rain in Southern California? And can we find the rain in Spain mainly in the plain? And what does that all mean for the people living in these places? Where does rain matter most for the population? In some places, it can be a much needed scarcity, elsewhere it appears in a much dreaded surplus. Wherever it is falling, rain matters a lot where people are. Partly, the global population distribution can be explained by climate patterns, with rain being a crucial factor for the agriculture in a region. In my presentation for the delegate’s session at this year’s 47th annual meeting of the British Society of Cartographers in Plymouth I took a closer look at the weather, or to be more precise, at climate patterns and their visualisation using gridded cartograms. Part of the presentation was an animation showing the global precipitation patterns projected on a gridded population cartogram. The following map shows the annual precipitation in relation to the global population distribution. The small map inset gives the conventional view of the same data, demonstrating how the perspective changes when seeing the same topic from two different views:

Map / Gridded Population Cartogram of Annual Rainfall (Precipitation) distribution in relation to people
(click for larger map)

The annual precipitation map shows, how most of the dry regions on the planet vanish when people are in the main focus of the map projection. Only few places show significant numbers of people living there, such as the Nile river delta region – which provides water (and fertile land) from the ground rather than from above. Regions affected by the monsoon rain in South and Southeast Asia in contrast are heavily populated, as this regular climate event provides the livelihood for wet rice agriculture and feeds billions of the world’s population.
More detailed interpretation of where and when most of the annual precipitation fall onto how many of us is possible, when viewing the data on a monthly basis using the same gridded population projection (using population data from SEDAC). Just as the above map, the following map animation visualises the precipitation data from 1950 to ~2000 to give a picture of the current climate conditions (precipitation data obtained from http://worldclim.org/). After the introductory annual image the animation shows month-by-month how the seasonal precipitation trends of affect the
world population (note the different scale for the total amount of rain between the annual and the monthly maps). Many details can be understood in their relation to people: the winter rains in the (European and North American) Mediterranean climates are still visible, as these are popular (and populous) places not only for holidaymakers. And large parts of the population in the northern hemisphere are exposed to some quite dry months throughout the year, something that the annual picture does not show sufficiently, but what is revealed in the monthly images. Similarly striking is the effect of the Asian Monsoon season that affects large parts of the world’s population. Many other details become apparent when watching the following animation more than once (and best in HD resolution):This video animation is also available on YouTube. The full series of maps from this animation will be added to this website next week. The remaining series of precipitation maps shown at SoC11 will also be added at a later time. Drop me a line if you attended the presentation and are interested in seeing the second part before it goes online here.
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