We will look at how CESM represents Potential Evapo-Transpiration (PET) and Aridity are represented in the 20th century in CESM compared to observations and reanalyses. We will also look at how aridity may evolve in the 21st century. The focus will be on arid regions (like central N. America and central China), as well as regions with high aridity sensitivity, including regions affected by shifting global circulation patterns.