Your best answer would absolutely lie on one of the topics presented by the World Meteorological Organization manual (WMO, 2009). Make sure you are selecting the appropriate orographic vs. non-orographic method before proceeding to the calibration as it's relatively easy to come up with huge estimates. Chapter 5 of the recently released consensus study report by the Committee on Modernizing PMP (National Academies of Sciences, Engineering, and Medicine, 2024) can also be of value for your calibration – page 84 onwards shows the uncertainty and sensitivity analysis that must be done, including when addressing climate change.

References (in Elsevier Harvard style format):

Committee on Modernizing Probable Maximum Precipitation Estimation, Board on Atmospheric Sciences and Climate, Water Science and Technology Board, Division on Earth and Life Studies, National Academies of Sciences, Engineering, and Medicine, 2024. Modernizing probable maximum precipitation estimation. National Academies Press, Washington, D.C. https://doi.org/10.17226/27460

World Meteorological Organization, 2009. Manual on estimation of the probable maximum precipitation (PMP). WMO, Geneva.

thank you very much, @ Bruno Oliveira Rodrigues