In the U.S., _____ aspects tend to be hotter and dryer and the fuels are drier and lighter.

• A. Northern
• B. Eastern
• C. Southern
• D. Western

Answer: (C)

Slope aspect strongly influences how hot and dry a hillside gets, which in turn controls how dry the fuels are. In the Northern Hemisphere, south-facing slopes receive the most direct sunlight, so they heat up more and lose moisture faster. That makes fuels—especially fine fuels like grasses, needles, and thin twigs—drier and lighter on these aspects, making them ignite more readily and burn with greater intensity. As a result, fires tend to spread faster on southern aspects than on cooler, moister north-facing slopes. Eastern aspects dry out early in the day with morning sun, while western aspects can become hot in the afternoon, but the overall driest conditions and quickest spread are typically found on southern aspects.