periodicity 'dekadal'?

[rabons]

Is your feature request related to a problem? Please describe. I would like to calculate SPI values on dekadal periodicity, i.e. every ten days of a month (days 1-10 are dekad 1, days 11-20 dekad 2, days >= 21 are dekad 3 of each month). This is often used in agricultural drought assessments.

Describe the solution you'd like Ideally, I would like to be able to run the spi command with --periodicity dekad, where the input netCDF file for precipitation is equally in dekadal time steps

Describe alternatives you've considered I may have to consider using a different package altogether.