Regional hydrology methods are stand-alone methods that, whilst containing all of the normal post-processing and data import features of the XP interface, are not as completely integrated into the XP engine. 

Although they produce results that are used in the sanitary and hydraulics layer via interface files they cannot be run simultaneously with the hydraulics layer and must be run sequentially. Of the 23 hydrology methods available in the software there are currently two methods implemented in this manner:

 The Sacramento County hydrology procedure can be enabled via the swmm.ini file.