Ten years of cumulative precipitation

We’ve all seen rain maps for a sliver of time. Screw that. I want to see the total amount of rainfall over a ten-year period. Bill Wheaton did just that in the video above, showing cumulative rainfall between 1960 and 1970. The cool part is that you see mountains appear, but they’re not actually mapped.

The hillshaded terrain (the growing hills and mountains) is based on the rainfall data, not on actual physical topography. In other words, hills and mountains are formed by the rainfall distribution itself and grow as the accumulated precipitation grows. High mountains and sharp edges occur where the distribution of precipitation varies substantially across short distances. Wide, broad plains and low hills are formed when the distribution of rainfall is relatively even across the landscape.

See also Wheaton’s video that shows four years of rain straight up.

Is there more recent data? It could be an interesting complement to the drought maps we saw a few months ago. [Thanks, Bill]


  • The color guide needs to have absolute numeric values, rather than categories relativized to the final distribution. But otherwise, this is quite nice to watch!

  • Also, having the rainfall visualized as hillslope really turns the concept of orographic rainfall on its head!

  • The slow reveal of mountain topography is a cool effect, granted, but I was distracted by the color scheme, particularly when I focused on locations in the South or in the Interior. The domain of cumulative precipitation values would be better represented, I think, by a sequential color scheme (from light, less precip; to dark, more precip). The dark brown symbol in this example is clearly out of quantitative sequence (i.e., compared to the lighter hued symbols on BOTH sides of it representing lesser and greater precip amounts). The result is a muddied representation, but visually and logically.

    Gridded monthly precipitation data are available (4km nominal cell size; 1895-2012) via the folks at OSU/PRISM Climate Group. http://www.prism.oregonstate.edu/index.phtml

  • Richard Giambrone January 29, 2013 at 8:48 am

    Really nice to watch. One suggestion. I would have flipped the color scheme to show dark green as being very wet instead of very dry. I think very wet, rain forest, green. Very dry, dessert, sand color.

    • Bill Wheaton February 20, 2013 at 8:58 am

      Hi– Thanks for the comment. The low (green) to high (white) color scheme was used because it is the way a lot of atlases portray elevation. Since the visualization in the video was portraying the precipitation as an elevation (z) value, I thought it would be interesting to see the colors as being symbolic of old-timey atlases. But, point taken regarding green often representing wet rather than dry.

  • Richard Giambrone January 29, 2013 at 8:48 am

    desert, not dessert! dessert is all colors! :)

  • john felleman January 29, 2013 at 12:40 pm

    It’s interesting, but the color scale used seems reversed. Dry areas should be reds, browns, wet areas green. If we look at a satellite photo, that’s what we’d expect.

    • Bill Wheaton February 20, 2013 at 9:00 am

      Hi — please have a look at my reply above for explanation of why I chose the color scheme I did. Obviously, browns/earth tones for dry areas would make sense as you suggest, but I was actually symbolizing rainfall as elevations which is why I chose the green-white color scheme. Thanks for the comment. I should try it using another color scheme (if I ever have time!).

  • Cool part for me is how closely the results resemble Bailey’s Ecoregions:

    • Bill Wheaton February 20, 2013 at 9:01 am

      Hi Andrew– thanks for that observation. I had not looked at it in conjunction with Bailey’s, but it is interesting. Maybe an area for future analysis?

  • 21st century data available?