aridification
/əˌrɪdɪfɪˈkeɪʃn/Climatology
noun
The process by which a climate or region becomes increasingly arid over a long period, especially as a result of natural processes (as opposed to human activity); specifically the long-term reduction of soil moisture.
Origin
Early 20th century; earliest use found in The Auk. From arid + -ification.