vpd

VPD is an acronym with multiple uses across different fields. One widely used meaning is Vapor Pressure Deficit, a term in plant science that describes the difference between the moisture the air can hold when saturated and the moisture it currently contains. It is calculated as VPD = es − ea, where es is the saturated vapor pressure at the air temperature and ea is the actual vapor pressure corresponding to the relative humidity. A common approximation for es is es = 0.6108 × exp(17.27T/(T+237.3)) in kilopascals, with ea = (RH/100) × es. VPD is expressed in kilopascals and is used to gauge transpiration and stomatal conductance. Values vary by crop and growth stage, but moderate VPD levels are generally preferred for many greenhouse crops; very high VPD can stress plants and very low VPD can increase disease risk.

Another prominent meaning is Virtual Private Database, a security feature in some database systems that enforces row-level access control by attaching policies to database objects. Under a VPD policy, queries are automatically augmented with predicates that restrict visible rows based on user identity or context, supporting data governance and multi-tenant security. While most closely associated with Oracle Database, similar row-level security mechanisms exist in other database platforms.

VPD can also appear in organizational contexts as the abbreviation for police departments, such as the Vancouver Police Department in Vancouver, British Columbia, and other agencies with the same initials. Context typically clarifies which VPD is intended.