# 2:2.2.4 Reading Measured or Estimated PET

Users are now able to read in daily measured or estimated potential evapotranspiration (PET) values from an external data source for each climate station. However, the user still has the option to calculate PET using the Penman Monteith, Priestley-Taylor, or Hargreaves method.  The equations used to generate PET data in SWAT+ are reviewed in Chapter 2:2.2.

Using measured or estimated PET allows the model to use real observed data, which can improve accuracy and reliability. By integrating measured data, the model can account for local variations in climatic conditions that might not be captured by theoretical methods. By incorporating this functionality, the model enhances its capability to simulate real-world conditions, making it a valuable tool for hydrological studies and water resource management.  SWAT+ input variables that pertain to measured or estimated PET are summarized in Table 2:2-3.

Table 2:2-3: SWAT+ input variables that pertain to measured or estimated PET.

| Description                                                   | Source Name | Input Name | Input File                                                            |
| ------------------------------------------------------------- | ----------- | ---------- | --------------------------------------------------------------------- |
| PET method; set to = 3 for reading in measured/estimated PET. | pet         | pet\_file  | [codes.bsn](/io-docs/introduction-1/basin-1/codes.bsn.md)             |
| Name of PET station                                           | petgage     | pet        | [weather-sta.cli](/io-docs/introduction-1/climate/weather-sta.cli.md) |
| File with PET measured/simulated data                         | petfile     | pet\_file  | pet.cli                                                               |


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://swatplus.gitbook.io/io-docs/theoretical-documentation/section-2-hydrology/chapter-2-2-evapotranspiration/2-2.2-potential-evapotranspiration/2-2.2.4-reading-measured-or-estimated-pet.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.