It has been observed that the temperature of a dry parcel of air, Which is made to rise, falls at a steady rate of 10°C for every km of ascent i.e., The adiabatic lapse rate of a dry parcel of air, or Dry Adiabatic Lapse Rate(DALR) is 10°C per KM.
The temperature of a saturated parcel of air, Which is made to rise, falls at a rate approx 5°C per KM.
Why is SALR less than DALR ?
SALR is less than DALR because, as the saturated air is cooled, its capacity to hold water vapour decreases and the excess moisture condenses into water droplets. This condensation releases latent heat that warms up the parcel of air. That is the reason SALR falls @ 5°C per KM. Where as DALR falls at 10°C per KM.