Civil Engineering - Water Resources Engineering - Discussion

How is it possible?

Temperature goes on decreases as altitude increases, I, e moisture increases so answer is B.

Humidity decreases with altitude. Here is an example:

A cubic meter of moisture saturated air at 15 degrees Celsius cannot contain more than 13 grams of water. If that air rises and cools down by the average adiabatic lapse rate of 0.65 C per 100 meters, when reaching 2,300 meters, the temperature will be 0 C (freezing point).
But at that temperature, the air is already saturated with only 5 grams per cubic meter. It means that, during that rising, the air must get rid of 13 - 5 = 8 grams of water per cubic meter.

And it does it by condensation and that's how clouds are forming!

So, the absolute humidity (volume of water per volume of air) decreases with the altitude but the relative humidity (percent of saturation point) stays the same in both cases since the air is still saturated and the relative humidity is 100 percent.

Absolute humidity is the total measure of water in the atmosphere (not percentage of saturation). As you get higher in altitude, the atmosphere becomes thinner (less pressure). This means that the total amount of water vapor the atmosphere can potentially hold is decreased.

Thanks @Roy.

Humidity is more at sea place.

Increasing height humidity is less at the mountain.