Final answer:
Warming an air parcel leads to an increase in its volume due to Charles's Law, an increase in its saturated vapor pressure allowing it to hold more water vapor, and a decrease in relative humidity since its capacity to hold water vapor is higher.
Step-by-step explanation:
When an air parcel is warmed, several things happen due to the principles of thermodynamics and gas laws. According to Charles's Law, the volume (VP) of a gas increases when the temperature (T) increases, provided the pressure remains constant. This is because the molecules within the air parcel move more rapidly and spread out as they gain energy from the heat, requiring more space.
In relation to the saturated vapor pressure (SVP), as temperature increases, the SVP also increases. This means that the air can hold more water vapor before it becomes saturated. Finally, the relative humidity (RH) will decrease if the air parcel is warmed because the air's increased capacity to hold water vapor (due to the increased SVP) makes the existing moisture a smaller percentage of the possible total, assuming moisture content remains constant.