Calculation of a 2-year, 24 hour storm is a lengthy process. See my comments above on this issue. Rainfall amounts, especially for one year, will not provide you with a 2-year, 24 hour storm event. This is information that you have to obtain from the local jursidiction. I have seen are some world atlas books that may provide a figure if there is no local jurisdiction, but they are not very accurate and should be used if you cannot obtain the information locally to your project.
I gave an example above for a 2-year, 24 hour storm for Baltimore. I found this value on the internet.
Hope this helps.