Which method can effectively reduce the relative humidity of the boundary layer?

Increasing temperature is an effective method for reducing the relative humidity of the boundary layer because relative humidity is defined as the amount of moisture in the air relative to its capacity to hold moisture at a given temperature. When the temperature of the air increases, its capacity to hold water vapor also increases. As a result, even if the amount of moisture in the air remains constant, the relative humidity will decrease due to the higher temperature.

In contrast, reducing pressure generally does not achieve the desired effect of decreasing relative humidity, and adding moisture will increase the relative humidity. Reducing surface area does not directly impact humidity levels either; rather, it might influence evaporation rates but not effectively alter relative humidity in the boundary layer context. Thus, the most effective method among the options provided is to increase the temperature.