High air pressure during summers is not a reason for scanty rainfall in western Rajasthan.
The western Rajasthan receives scanty rainfall due to the following factors—
1. The presence of Aravalli hills acts as a barrier to the monsoon winds and western Rajasthan in the rainshadow zone. 2. The location of the Aravalli range is parallel to monsoon winds 3. Due to scorching heat as most of the moisture of the winds is evaporated. 4. Few trees are also the main cause of scanty rainfall as trees contribute a lot in the water cycle (through transpiration).