Saturday, March 17, 2018

"Weathering the Storms" (Dragon #137) and the Köppen Climate Classification System

The second major inspiration for what would later become THE ALMANAC of FANTASY WEATHER was Lisa Cabala's article "Weathering the Storms" in The Dragon #137.

The central insight of the article was to present twelve climate templates, templates that both tracked the different climate tyoes of our own world as well as (presumably) any half-way "realistic" fantasy world. The climate templates were these:

  1. Desert
  2. Tropical Savanna
  3. Steppes
  4. Equator
  5. Warm and Rainy
  6. Monsoon
  7. Warm with Dry Summer
  8. Warm with Dry Winter
  9. Cool and Rainy
  10. Cool with Dry Winter
  11. Tundra
  12. Polar
Each type was defined by its temperature ranges within the four standard seasons as well as the daily precipitation chances within those seasons. Those two variables and how they changed or varied (or didn't) from season to season constituted the basics of any climate type, and simply by presenting twelve of those types you could track the richness and diversity of all the earth's climates, or so it seemed.

For example, much of Western Europe was Warm and Rainy (5):

Unlike some other climate types, Warm and Rainy had a simple precipitation rate scheme. Daily chance of precipitation was a constant 40% throughout the year.

That's it.

I found this to be an improvement over what I saw as the more fiddly mechanism for determining temperature presented by David Axler in his "Weather in the World of Greyhawk" (The Dragon #68). There, the referee would, among other things, constantly be checking latitudes. Cabala's scheme also seemed more true to life. While latitude obviously affects temperature, in our own world wildly different climate types co-exist at identical latitudes. And in turn, very similar climate types appear at quite different latitudes.

So, the original design for my fantasy weather algorithm was to enter the climate data for the twelve climate types and then choose the appropriate one for each geographical location I wanted to model. If the average temperature for one or more seasons came out significantly different than that shown by the data for the location, I would simply make the appropriate adjustments.

However, in my quest for greater "realism," I soon became a bit dissatisfied with the list. As I found myself making more and more "adjustments" it became clear to me that the twelve templates offered worn't really enough. There were hot deserts and cold deserts, for example.

Somewhere along the line I discovered the Köppen Climate Classification System. In the late 19th century, the Russian-German climatologist Wladimir Köppen had also separated the world into different climate types. After the system was modified and refined by others, there were a resulting thirty climate types (or thirty-two, depending on how you counted them). Here were hot deserts and cold deserts (and hot semi-deserts and cold semi-deserts), among other things.

My inner weather nerd (yet another inner nerd this outer nerd never knew it had) became excited.

Again, one of the things that is fascinating about the climate types (if you're into this sort of thing) was how they didn't track latitude, at least as much as you would think. The world map above sort of gives you a sense of that, though it's more apparent if you focus on a smaller area. Such things as warm and cold ocean currents, wind patterns and so on are often much more important.

This is of course a commonplace for anyone with even a minimal knowledge of weather and climate, but it was useful and interesting to be reminded. 

I suspect Cabala had riffed off of Köppen but had wisely chosen to simplify it for her Dragon article. Thirty templates would have been too many for a scheme that required one to consult charts and roll dice. But if I were designing a relatively complex algorithm from scratch, starting with thirty sets of data wasn't that much more difficult than starting with twelve.

I would later make things even more granular to model different areas within each type - London versus Paris, for example - in order to make each location modeled truly "its own." And in the end, the classifications themselves would fall out as I settled on basing each of my own climate templates on the raw climate data for the particular location modeled, as opposed to its Köppen classification (which used the same sort of data but in a more general manner).

So, for example, I used Athens, Greece as a model for my internal Köppen template of Csa - Temperate, Dry and Hot Summer:   

But when creating my own Climate Template 101: Temperate South, which I roughly modeled on the climate of Jerusalem (also classified as Csa), I entered an entirely new set of data:

Would anyone have known that Temperate South, which I claimed to have roughly modeled on Jerusalem, was in fact really roughly modeled on Athens?

Yes. I would have. God would have.

Okay, even God probably wouldn't have cared, but still.

THE ALMANAC of FANTASY WEATHER: Volume 1, Swords & Sorcery was intended to simulate Middle-Eastern, Central Asian, Robert Howard-ish, Fritz Leiber-ish, "Swords & Sorcery"-ish sorts of climates. And, dammit, Athens didn't really fit. Entering the data for a second Csa climate type only took an extra hour or so.

And now, that one weather nerd out there who knows that it never would get down to -11 F in Jerusalem can't complain.   

But readers of THE ALMANAC of FANTASY WEATHER will notice that each of my own climate templates is also labeled with the Köppen type that it fits.

Tomorrow, the excitement level ramps up. Yes, I'm talking about temperature.

Friday, March 16, 2018

"Weather in the World of Greyhawk" from Dragon #68

As I might have mentioned before, the idea for designing what would eventually become THE ALMANAC of FANTASY WEATHER came to me when I was re-imagining druid spells for the Book of Spells supplement to SEVEN VOYAGES of ZYLARTHEN. Many of the spells were directly or indirectly linked with weather, which naturally brought up the question - how do you know what the weather is?

As far as I know, none of the original rulebooks for old-school D&D - OD&D, Holmes, B/X or AD&D offered a weather generation mechanism (I didn't go back and check this, so it's possible I'm wrong), which is sort of odd considering that some of the books, such as the DMG, went into such great detail on other things.

However, an article by David Axler, "Weather in the World of Greyhawk" in The Dragon #68, offered a detailed and robust system. As I understand it, that system had been or would be also incorporated into the Greyhawk boxed set. This was where I started.

Readers of FANTASY WEATHER may note that I took many of the same names for precipitation events from that article - Light Rainstorm, Heavy Rainstorm, Light Blizzard, Heavy Blizzard and so on. Since my original intention was not to design a commercial product, I didn't initially worry about copyright, but when I did start to think about that, the naming conventions seemed generic enough to be fair game, and I did notice that much of the same list was used in some of the other newer non-TSR weather products.

I soon altered the list however. Some of the names seemed too American or Western - Hurricane, Tropical Storm, Tornado, etc. - or too obviously culturally specific - Monsoon - for the tone I was trying to set. I didn't want FANTASY WEATHER to sound like the weather report from a North Carolina CBS affiliate, or an AP report from Bangalore. And I folded the article's "special weather" into the more general list. If you used the calculation scheme of the original article, a desert would only get a sandstorm once every eight years, or so I figured it. Where's the fun in that?

I used the article's durations, rainfall/snowfall amounts, wind speed ranges and the like for each precipitation event as a jumping off point, but soon started to fiddle with them for various reasons. For example, I soon discovered that while the rainfall amounts initially seemed realistic, if you did the math, the amount of yearly rainfall for pretty much anywhere in Greyhawk would be off virtually any terrestrial scale - often more rain (in inches or millimeters) than even the wettest place on earth. One of the first things I designed was a method to quickly alter rainfall and snowfall amounts to fit the data for the climate type being simulated. For example, if the weather results for a London-type climate yielded 400 inches of rain on average (roughly ten times the actual total) you could simply divide the rainfall for each event by ten. Of course, you could also just make precipitation events less likely (by a factor of ten) but that possibility wasn't attractive. London is pretty rainy. That doesn't mean you get a huge amount of annual rainfall, measured in inches or millimeters (it's less than New York), but it does mean that you have 150-200 at least slightly wet days per year. Reducing that to 15-20, which would have amounted to desert conditions, didn't seem right.

I realize that the last consideration is more for weather nerds or "realism" nerds. It's unlikely that many readers, referees or players would know or care that the sum of the daily rainfall totals wasn't "realistic." But I figured if I was going to do it, I might as well get it right.

"Weather in the World of Greyhawk" also gave me the idea for those funky rainbows (including that 1 in a 1000 chance of a Bifröst bridge), which I thought, if nothing else, added a fun flavor to things. So I left the idea intact, though I did twiddle the percentages. Later I would add in "supernatural causes", again, suggested by the article, although I substantially modified their chances and content. And I significantly changed how lightning worked. I wanted there to be at least a chance of it in most rain-event types, not just in thunderstorms. Again, this seemed to better match the real-world data, at least as I understood it.

And, of course, I found the article's mechanism for generating each day's weather with dice to be utterly impractical. It just took way too long. That's not the article's fault per se, of course, simply an unavoidable factor of real-world physical realty. That you could do it virtually through an algorithm coded into an Excel Spreadsheet, and then present it clearly in "almanac" form, was the whole idea behind FANTASY WEATHER.

That's the sum of it. I don't mean to sound critical of what in my view was the best treatment of weather and climate to ever appear in a TSR product. Along with a later article, which I'll talk about in the next post, it gave me the framework for how I would look at the problem of fantasy weather. The central insight of the article for me was framing the thing around "precipitation events" and their properties. But there's a lot more to the article than that that either I didn't talk about here or didn't find relevant for the FANTASY WEATHER project but that is still quite interesting and useful in its own right.

If you have The Dragon #68 in hard copy or have access to the PDF, I urge you to read or re-read it.

Tomorrow: "Weathering the Storms" and Köppen climate types.

Thursday, March 8, 2018

THE ALMANAC of FANTASY WEATHER is now live on DriveThruRPG

Campion & Clitherow has just released THE ALMANAC of FANTASY WEATHER. It's available on DriveThruRPG and Lulu.

THE ALMANAC of FANTASY WEATHER is a new and greatly expanded edition of SEVEN YEARS of FANTASY WEATHER, published by Campion & Clitherow in 2017. The most obvious difference is that while SEVEN YEARS included seven years of weather for one geographical area or climate type, THE ALMANAC has eight years of weather for each of ten different climate types. Here you will find cyclone lashed coasts, burning deserts, steaming jungles, ice-covered wastes and more—enough (we hope) to provide realistic and interesting weather for an entire “Sword & Sorcery” world in the style of Burroughs, Howard or Leiber.

We have also made some other changes. Some of them are “internal” and, therefore, not immediately noticeable. I think the data sets and algorithm for SEVEN YEARS were pretty rich, but we couldn't resist tweaking them and expanding on them. We increased the number of data points and redesigned the internal format for how initial information for each climate type was represented, allowing for more diversity, complexity and pattern in the generated weather results. Thus, many precipitation events now come at the head of “real” warm and cold fronts, cloud cover varies by month and season, wind speed and precipitation often vary according to whether it is day or evening, “exogenous” factors may cause cold or warm spells for days, weeks or months, and so on.

The most noticeable external changes to the weather charts are a slightly expanded list of precipitation types, the addition of a wind-chill/heat index rating and the addition of a new category of weather events—those directly caused by “supernatural” forces.

THE ALMANAC clocks in at 1,130 extensively bookmarked virtual pages (960 pages of weather charts - 12 x 8 x 10 - plus 70 pages of text, climate summaries and spaces for notes). It sounds like a sort of monster, and in a way it is, but the bookmarks allow you to get around quickly to find or use (on your phone, tablet, computer or hard-copy print-out) only what you want or need at the moment.

Because of its size and diversity, I think it makes for a more useful product, giving the referee many more options to choose from and match with the specifics of his or her campaign. I should note, though, that the climate types and weather charts for MEDIEVAL ENGLAND, THE ICELAND OF THE SAGAS and INDEA remain unique, and have not been "rolled-in" to THE ALMANAC.

Previous purchasers of SEVEN YEARS may purchase THE ALMANAC at a discount ($12.95 - the list price of $19.95 less the $7.00 price of SEVEN YEARS).

An email has just gone out to most purchasers of SEVEN YEARS on DriveThruRPG. However some purchasers did not include contact information on the DriveThruRPG list. If you purchased SEVEN YEARS and do not receive an email in the next few hours, send me an email at and I'll shoot you the discount code.

These tables (from the Introduction) detail some characteristics of the new climate types:

And here are two months of weather from "Climate Template 102: Southern Desert", roughly modeled on the Arabian Desert:

The desert has a higher proportion of relatively rare "supernatural" weather events. (They occur, on average, roughly twice a year in most other climates but roughly six times a year in the desert.) The "ef" next to whirlwind denotes that it was caused by an Efreeti. Why was there a sudden downpour? Because it was caused by a demon or demons ("dm"). Obviously, the player-characters may not know that an event had a direct supernatural cause, though there may be signs - the clouds form unusually quickly, they can dimly see an outline of a figure or figures in the sky, etc. As always, the referee is free to alter or mix and match things to suit the specifics of his or her campaign, and ideas for how to do this are included in the introductory notes.

I had a blast designing THE ALMANAC of FANTASY WEATHER. It brought out by inner weather nerd (which I never knew existed). And I'm very excited by how it turned out.

I hope you enjoy it!