Adventuring in Hostile Climates

Mountain Path by Reza Afshar

The campaign I am currently writing takes place in the frozen fjords of the north-lands (I know, it doesn’t sound like a terribly original setting). When the players venture out into the mountains they’ll be walking through thick snow, howling winds and blizzards. But how do you represent this with in-game mechanics? I’m not fond of the “roll a constitution save vs the environment every hour” approach; a naked adventurer with a high constitution bonus shouldn’t be able to wander your world’s not-Antarctica just by luck of the dice. Going to the other extreme, I’d rather not stat every item of clothing the players are wearing and it’s relative insulation values. Hopefully this system also avoids the players feeling that “You’re now freezing and will take penalties to dexterity checks” is pure GM fiat (or spite).
Since the area will be available as a hex map, should the players feel the need to strike out into the wilderness, I’d also like a system that can be summarised easily on the map itself, preferably as annotations on each hex.



The system I’ve worked out has two sections: the Environment and the Adventurers. I’ll also note what I’ve assumed and what I’ve purposely ignored to try and keep this system as lightweight as possible.

The Environment

Each hex has 4 stats required:

• Precipitation – 2 percentages – roll a d100 under the first for heavy precipitation, between the two for light precipitation and above the second for sunny weather. The type of precipitation will depend on the temperature.
  
• Wind speed – Similar to Precipitation, rolling a d100 under the first percentage means high winds, between the two means low winds, above the second means no wind (or at least, not enough to affect the PCs in any meaningful way).
  
• Temperature - Given as two numbers this is the average Ambient Temperature Modifier during the day and during the night, on a scale explained below. Roll 2d6 -7 then add this number to get the Temperature Modifier. (2d6 -7 gives a 10 point variance weighted nicely to 0 in the middle. AnyDice.com is great for visualising statistical distributions like this.)
  
• Terrain type – The picture on the hex itself. It comes into play for specific conditions, for example high wind in a desert might whip up a sandstorm.
  

Examples:

There are a couple of ways to present this information. One is as a GM overlay on the hex map:

Imagine this but with decent artwork.

Another would be to number each hex (which I'd normally do anyway) and include the stats as the first part of each description in the index. It would mean having to reference a second page but your map would look neater.

Environmental Conditions:

The general stats above lead to specific Conditions and their associated Effects. It’s generally pretty obvious when the different conditions will trigger.

*Wind can be cooling or heating depending on what ambient temperature is and where the wind is blowing from.

Environmental Effects:

Cooling = -2 heat
Chilling = -5 heat
Heating = +2 heat
Scorching = +5 heat
Blinding = Adventurers are unable to see anything beyond a few metres.
Deafening = Adventurers are unable to hear anything beyond a few metres.

Summary

The environmental modifier = The Ambient Temperature Mod + modifiers from Environmental Effects +/- your Con bonus (whichever would bring it closer to 0).
Unless you’re in a highly unstable environment I wouldn’t roll for this more than once or twice per in-game day (and again at night).

The Adventurers:

Death	Frostbite	Freezing	Normal	Overheating	Heatstroke	Death
-20	-15	-10	0	10	15	20

This is the scale your players will care about. I’ll explain below what happens at each stage and how to work out where your players are on it.
The following conditions are cumulative from Normal, so someone at Frostbite will also suffer the effects from Freezing.



Frostbite: Every hour roll a Con save to determine if one of your fingers/toes falls off.
Freezing: It’s hard to be sprightly when you can’t feel your legs; your movement suffers and you face disadvantage for any Dexterity-based tasks.
Normal: No penalties.
Overheating: You start getting faint and losing your focus; perception suffers and you face disadvantage for any concentration-based tasks. You also need to drink more.
Heatstroke: Every hour roll a Con save to stay conscious.

Player Temperature Modifiers:

Light armour: +1
Medium armour: +3
Heavy armour: +5
Some sort of thermal wear (furs, padded clothing): +5
Cloak/overcoat: +2
Loose desert clothing: -2
Constitution Bonus: This pulls your temperature back towards Normal (0), so if you’re cold you would add the bonus and if you’re hot you would take it away.

Active measures:

Some ideas for things other than clothing that the players might try to control their temperature. Expect the players to come up with much more ingenious situational solutions.

Shelter: Removes weather effect modifiers (as long as it’s reasonably weather-proof), brings ambient temperature modifier to -2 maximum.

Campfire: +5 heat for the whole party, or as many as want to sit by the fire.

Dousing in water - -5 for an hour but consumes a ration of water

Shade/Parasol - Removes sun modifier, takes up 1 hand unless the player can work up some non-contact shade that doesn’t require holding.

Notes:

• The eagle-eyed among you will note that it would take walking around on top of a mountain, in the snow and howling wind, on a cold night, wearing nothing but a Hawaiian shirt, with a Con bonus of 0 to bring you to Death at -20. I believe it should take some really special circumstances (or incredible stupidity) for the adventurers to be killed by the weather, otherwise the game risks shifting the focus from adventuring to wilderness survival (which is a valid focus, just not the one I want for this campaign.)
  
• While you could put these stats on every hex on your map, I envisage them only being used for obviously extreme-weather areas (deserts, mountain tops, glaciers).
  
• Other than the Ambient Temperature Modifier, individual modifiers should generally range from 0 to +/-5, anything more than that should take a combination of different effects.
  
• Effects should only come in after an hour, not during the length of a combat (allowing the player to remove some heavy thermal clothing or don armour for a fight), but effects already in-place will affect a combat.
  
• Elemental spells do not alter the track unless they're sustained and area-effect. (Someone on fire probably doesn't care about sweating because of their heavy armour)
  

Things I've intentionally missed out that you might want to consider for a more in-depth experience:

• Stat penalties for different effects. This should be easy enough for you to figure out on-the-fly if that’s how you want to implement it.
  
• Rain effects on bow/crossbow users (see the Battle of Crécy.)
  
• Stamina effects from being slightly hot or cold (probably a penalty to hustling/overland travel.)
  
• Piecemeal heat benefits from different types of armour and the heat-sinking properties of metal armour.
  
• Major effects like tornadoes, thunderstorms, hurricanes, floods etc. These are better run as an encounter or special conditions rather than as part of the environment.
  
• Differing weather patterns for the day and the night. I realise that in some places snow is more likely overnight than during the day but a) I can’t think of a way to encode that neatly into a hex-map and b) I’m not a meteorologist so I honestly don’t care that much.
  
• Magical areas. These differ so much world to world that I don’t want to limit them. Hopefully this system would be easy enough to extend for magical effects.