According to the ESRT's (Earth Science Reference Tables), dry regions on Earth are usually a result of winds/air that:
a) converge and sink
Dry regions on Earth are often associated with areas where air converges and then sinks. As air descends, it becomes warmer and has the ability to hold more moisture. Consequently, the descending air warms up, leading to evaporation of any existing moisture, resulting in dry conditions. This process is known as subsidence, and it is commonly observed in regions like deserts where dry climates prevail due to the sinking air masses.
