Which factor can increase relative humidity on slopes?

Relative humidity can be influenced by various environmental factors, and shading on northern aspects plays a significant role in increasing humidity levels in these areas. When the sun's rays hit slopes, they can cause the moisture in the air to evaporate, leading to lower humidity. However, northern aspects receive less sunlight, especially during certain times of the year, which means they retain moisture more effectively. The shade provided by surrounding vegetation and terrain can help maintain a cooler microclimate, reducing evaporation rates and allowing relative humidity to rise.

In contrast, while vegetation type may influence moisture retention to some extent, it does not alone account for the larger-scale effects of shading from the sun on these slopes. The steepness of the slope can affect drainage and run-off but does not have a direct relationship with relative humidity. The amount of available fuel, while relevant to fire behavior, is not a factor in determining humidity levels. Therefore, the key to understanding the increase in relative humidity on slopes lies in the cooling and protective effects of shading on northern aspects.