Scope
Where this method applies
Use for plant-environment observation and comparison; retain whether the calculation uses air temperature alone or a leaf-temperature estimate/measurement.
Environment measurement · THC SOP
VPD Observation Record
Create a transparent vapor-pressure-deficit record that preserves the temperature and humidity inputs rather than storing only a derived VPD number.
Frequency
When to run it
Use when characterizing climate periods, investigating water relations, or comparing environmental changes.
Preparation
Tools and preconditions
Required tools
- air temperature/RH sensor
- leaf-temperature method when leaf-to-air VPD is required
- validated VPD calculation method
- record sheet
Before starting
- Confirm temperature and RH measurements represent the intended microclimate.
- Record whether leaf temperature is measured, estimated, or omitted.
Procedure
Run the method in order
Step 1
Capture inputs
Record air temperature, RH, time, and sensor location; record leaf temperature and leaf location when available.
Record: Preserve all raw inputs and units.
Step 2
Choose calculation basis
Document whether the value is air VPD or a leaf-to-air formulation and which temperature is used for saturation vapor pressure.
Record: Record calculation basis or tool/version.
Step 3
Calculate
Calculate VPD using the documented inputs and method.
Record: Record VPD and units alongside the raw inputs.
Step 4
Interpret in context
Compare values through time together with plant water status, light, airflow, and irrigation observations rather than treating VPD as a stand-alone diagnosis.
Record: Record relevant contextual observations.
Quality control
Verification checks
Raw temperature and RH inputs accompany the derived VPD.
Leaf temperature status is explicit.
Units and calculation basis are recorded.
Evidence record
Fields to preserve
- air temperature
- RH
- leaf temperature/status
- VPD
- calculation basis
- sensor locations
- time
- plant/context notes
Interpretation boundary
Limitations
VPD is a physical environmental descriptor, not a diagnosis and not a complete model of stomatal behavior or plant water status.
Connected learning