Precipitation Patterns in 175 Cities

If you’re like me, you’ve at some point in the past looked at a precipitation table for a city and thought “Wow, I don’t actually know how much that means.” Unlike temperature, precipitation level is not actually well-conveyed by a number; most people don’t see a number that represents an amount of precipitation and immediately get a sense of whether that’s large or small. (“It rained 0.8 inches today? Is that a lot or a little?”) Futher, even people who readily convert between Celsius and Fahrenheit don’t often convert between millimeters and inches that well, so comparing statistics for cities outside the US with cities in the US actually requires calculation.

So here’s an attempt to solve this problem. The following chart is color-coded to represent which biomes have precipitation amounts comparable to each monthly average.

Extreme-Desert-Level Precipitation (<8 mm/month)
Desert-Level Precipitation (8-15 mm/month)
Shrubland-Level Precipitation (16-31 mm/month)
Grassland-Level Precipitation (32-95 mm/month)
Deciduous-Forest-Level Precipitation (96-191 mm/month)
Rainforest-Level Precipitation (192-383 mm/month)
Extreme-Rainforest-Level Precipitation (≥384 mm/month)

This should help make the numbers instantly recognizable as large or small. In addition, the juxtaposition of all 175 cities together in one document makes their monthly precipitation averages easily comparable.

Monthly Precipitation Averages in 175 Cities

A few notes on standards:

  1. I made several choices in standards in the generation of this document. I am a strong proponent of using endonyms (native names) of countries and cities for purposes of respect and for diluting what I consider excessive Anglocentrism, and on top of that also an advocate of using the native script to display these names (with Romanized names attached for recognizability). I chose not to do that in exchange for the value of generating the document in a non-proprietary font, which unfortunately are rather lacking in scripts supported. Thus, countries and cities are displayed in their English names.
  2. Ideally, month statistics will align with or midmonth-align with dates of equinoxes, for maximally naturally sensible bins in which to group data points. Unfortunately, this sort of data is not available, only numbers for dumbly-divided months some of which have length 31 days and some of which have length 28 days.
  3. To keep the groups for four seasons intact, I moved December to the first column of rows. Although official definitions for the starts of seasons are at corresponding solstice or equinox, I chose to err early rather than late in relation to this definition because climatological data seems to suggest that at least a temperature-based division of seasons would center them on January, April, July, and October (some data on American cities).

2 thoughts on “Precipitation Patterns in 175 Cities”

  1. I’m surprised that Washington, DC and Philadelphia and Boston only get grassland-level rainfall, since these cities have forest as their “normal” ground cover.

    1. Note that they straddle the grassland-deciduous forest boundary, and that the grassland numbers are generally in the far high end of the range. I prioritized having cutoffs be round numbers so that category numerical covers are comparable, and settled on a way of approximating such that the green category was the only category occupying a different amount of logarithmic number-space, but that was still a fairly round number. In the process, the grassland/deciduous forest boundary is pushed up a bit from where it should really be, but the intended goal of giving a feel of whether precipitation is large or small is preserved.

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