Extreme Heat

Temperatures at or above 100°F (38°C) present a serious hazard to unprotected characters.

Saving throws: A creature exposed to extreme heat without access to water must make a Constitution saving throw at the end of each hour spent in the heat. The DC starts at 5 and increases by 1 for each subsequent hour.

On failure: The creature gains one level of exhaustion.

Modifiers:

• Creatures wearing medium or heavy armor or heavy clothing have disadvantage on the saving throw.
• Creatures with resistance or immunity to fire damage automatically succeed.
• Adequate water supply reduces risk (DM discretion on exact impact).

Cumulative danger: Because the DC increases each hour and exhaustion stacks, characters can deteriorate rapidly. After 6 hours without relief, the DCs become quite high (DC 10+), and multiple levels of exhaustion severely impair the character.

Water requirements: In extreme heat, characters require 2 gallons of water per day (double the normal 1 gallon). Going without adequate water in heat triggers dehydration faster — exhaustion after half a day instead of a full day.

DM tips: Extreme heat is most impactful as a multi-hour travel hazard. It pairs well with water-scarcity scenarios, desert exploration, and volcanic environments. The create water spell and Outlander's Wanderer feature can mitigate these hazards.