How does the IDF Curve Tool handle incomplete years?
In short: The IDF Curve Tool checks whether the first and last years are complete under the selected calendar, water, or custom-start year. When it detects partial boundary years, it lists them in a warning and automatically selects Exclude incomplete years for distribution fitting.
Why partial years can bias an IDF analysis
An incomplete year may omit the period when the true annual maximum occurred. Its calculated maximum can therefore be too low. Including several such values can pull the fitted IDF curve downward, with potentially important effects at longer return periods.
What the exclusion changes
The exclusion applies to the affected years in the frequency-distribution fit. The checkbox can be cleared when there is a documented reason to retain a partial year, but exclusion is the safer default for an annual-maximum-series analysis. This automatic check focuses on partial first and last years; analysts should still quality-control internal gaps and long missing periods throughout the record.
Completeness is evaluated using the chosen year starting month. Changing from a calendar year to a water year can therefore change which boundary records are considered partial.
See the Incomplete Years Warning section for the exact workflow.
Use the IDF Curve Tool to inspect and manage incomplete analysis years.