What books unrelated to TTRPGs are the most useful to you for TTRPGs?

[Nytmare]

One thing that always perplexed me was how rainfall is measured. I remember reading the FR boxed set the Lands of Intrigue and IDR whether it was the Amn or Tethyr book but they said country "X" receives "Y" inches of rainfall a year. How exactly is that measured? Put a graduated cylinder during any given rainfall and its likely to fill up. I've looked it up and still don't get it. Can you explain it?

Rainfall is exactly that. Put out something that collects water and see how many inches of water you end up with. There are some minor complications due to airflow, environment, and level, but that's what it's measuring.

It's not going to give you a super accurate measurement, but if you imagine an empty birdbath in a rainstorm, the amount of water that's in it when the rain stops is how much rain you've gotten.

 

[aramis erak]

One thing that always perplexed me was how rainfall is measured. I remember reading the FR boxed set the Lands of Intrigue and IDR whether it was the Amn or Tethyr book but they said country "X" receives "Y" inches of rainfall a year. How exactly is that measured? Put a graduated cylinder during any given rainfall and its likely to fill up. I've looked it up and still don't get it. Can you explain it?

The graduated cylinder is how you measure it.
A typical light rain shower is under 0.1" (2.5mm) per hour, usually for under 30 min. A typical heavy torrential rainfall is 0.3" (7.5mm) per hour.

Note that, for example, Corvallis, Oregon, gets 51" of rain per year. It gets 159 days of sun, so that's 206 days without sun, and about 1/3 of those are actually rainy... so about 70 days per year of rain.. which means a typical rain day is .7" (~18mm) over the day. Typical rainy days aren't solid rain, but about 4-12 hours of rain as the front passes. .7" in 4 hours is going to drench you, and that's dumping 3.3 gallons per sq. yard (~15 l/m²)...

1" of water is 4.7 gal/yd²; 1cm of water is 10,000 cm³ per m², or 10 l/m².

So if the rainfall is under 12" per year, the land is very likely to be dry - grassland, scrub or desert.
If the rainfall is over 24" per year, it's likely to be forested or grasslands, based upon other factors. At 50" per year, flooding, usually annual, is to be expected; flooding is often minor, as well.

The peak is 11.871m/year... 466"/year... more than 1" per day... and is dense jungle. Note, however, that most places have sunlight at least 1/5 of the time. Average overland is 28" per year.

 

[Lanefan]

One thing that always perplexed me was how rainfall is measured. I remember reading the FR boxed set the Lands of Intrigue and IDR whether it was the Amn or Tethyr book but they said country "X" receives "Y" inches of rainfall a year. How exactly is that measured? Put a graduated cylinder during any given rainfall and its likely to fill up. I've looked it up and still don't get it. Can you explain it?

If you put out a simple gradated cylinder during a rainfall and it fills up, you've just received one hell of a lot of rain!

There's two ways of doing it. One is to simply have a marked transparent cylinder - which has to be kept perfectly vertical - and see how much water it collects; emptying it out after each measurement (more precision can be gained by having a bigger opening and then funnel the water it catches into a gradated cylinder, with the gradations adjusted to allow for the bigger catchment area). Another, much fancier, way of doing it is to have a container of any shape but whose "catchment area" (the size of the opening at the top) is known to the tiniest measure, carefully weighing what the container gathers, and then mathematically converting that weight of water into inches of rainfall.

In either case the measurement needs to be taken soon after the rain stops, before evaporation sets in.

 

[Lanefan]

The graduated cylinder is how you measure it.
A typical light rain shower is under 0.1" (2.5mm) per hour, usually for under 30 min. A typical heavy torrential rainfall is 0.3" (7.5mm) per hour.

Note that, for example, Corvallis, Oregon, gets 51" of rain per year. It gets 159 days of sun, so that's 206 days without sun, and about 1/3 of those are actually rainy... so about 70 days per year of rain.. which means a typical rain day is .7" (~18mm) over the day. Typical rainy days aren't solid rain, but about 4-12 hours of rain as the front passes. .7" in 4 hours is going to drench you, and that's dumping 3.3 gallons per sq. yard (~15 l/m²)...

To be pedantic, unless Corvallis is incredibly cloudy that 159 days of sun occurs across more than 159 days; it's not that each individual day is entirely sunny or entirely cloudy.

So if the rainfall is under 12" per year, the land is very likely to be dry - grassland, scrub or desert.

To expand a bit here: the climatological cutoff for "desert" is anything less than 10" per year (might have been tweaked slightly for metric but close enough); and the range for "semi-arid" is between 10" and 20" per year. Most grassland is semi-arid.

That said, some desert and-or semi-arid areas can get their entire annual rainfall in just one or two events.

If the rainfall is over 24" per year, it's likely to be forested or grasslands, based upon other factors. At 50" per year, flooding, usually annual, is to be expected; flooding is often minor, as well.

For world-building purposes, it's also worth noting there can be quite significant variants in annual precip even within just a few miles. For example in Victoria BC, where I live, there's a weather station downtown and another at the airport some 20 miles north; and the airport station gets about 1/3 more per year than downtown (used to be about 25" vs about 34" back when I paid attention) due to downtown being closer to the rain shadow generated by the Olympic mountains. There's a couple of places on the Washington side, about 20 miles south of downtown Vic. and deeper in that rain shadow, where the annual precip is well under 20".

 

[aramis erak]

To expand a bit here: the climatological cutoff for "desert" is anything less than 10" per year (might have been tweaked slightly for metric but close enough); and the range for "semi-arid" is between 10" and 20" per year. Most grassland is semi-arid.

That said, some desert and-or semi-arid areas can get their entire annual rainfall in just one or two events.

When I took Env. Geo, it was 12", not 10". Fairbanks, Alaska runs 10.8" per annum... but is largely wetlands. How? Why? It's the bottom of a drainage bowl, and where most of the evaporation happens... for a more than 100-mile across bowl. Almost all the snowmelt flows through Fairbanks and Nenana.

 

[Alzrius]

I'll note that anyone looking for some tables on weather should check out the materials from Campion & Clitherow, particularly The Almanac of Fantasy Weather Volume One: Swords & Sorcery and Volume Two: Europe. These massive books (over 1,100 pages!) give eight years' worth of weather for ten different climates, each.

If those are too much, they have several shorter weather supplements with a tighter focus, those being Seven Years of Fantasy Weather Volume 1: Medieval England, Volume 2: The Iceland of the Sagas, and Volume 3: Indea.

And yes, these include overviews of the average level of rainfall!

Please note my use of affiliate links in this post.

 

[R_J_K75]

@Nytmare, @Lanefan & @aramis erak thanks for the explanations they were very informative.

 

[JiffyPopTart]

I read a lot of WW2 historic books, and whenever an interesting raid or battle or plan or whatever comes up I almost always use that as a basis for an RPG story.

As an example, the Japanese holed up in the bunkers on Iwo Jima sparked a Cthulhu one-off that was about what those desperate soldiers would do to not starve when deals with deep ones were an option to keep them alive.

 

[Ulfgeir]

Well for me, it would be my shelf with books of Art/Architecture/Fashion through the ages, as well as my shelf with various books about weapons/martial arts/mediaeval swordfighting (yes, I have a few manuals on it)...

I also have lots of books of history and various mythologies.

Of course a lot of these books are on my to-read list. but they do make good reference-books,

 

[Shiroiken]

Not a "book" per say, but I've found comics to be an amazing source of inspiration. The trick is to use the concept, without the specifics, to keep players from figuring it out. I ran the Knightfall story arc without anyone figuring it out until the very end, and everyone loved it.

Not a book but I use Wikipedia and the internet for reference all the time when writing adventures. I don't need (nor want to read an entire book) for one specific piece of real world information I can translate to my fantasy game.

I used to look up various information scattered across dozens of books for IRL information to use. Wikipedia has made all of that obsolete, becoming the "go to" for details I need. Sometimes it gives a lot of surprises (for example, the military pick is just the opposite side of a war hammer).