"TRIP" stands for "Total Runoff Integrating Pathways". These pathways can help to isolate the river basins, inter-basin translation of water through river channels, as well as collect and route runoff to the river mouth(s) for all the major rivers (essentially converting land runoff to river discharge). TRIP enables us to validate the runoff part of land surface parameterizations (LSPs) in GCMs.
Two major versions of TRIP exist, first one uses constant river velocity throughout the world, and the second (named TRIP2) calculates the velocity on each grid depending upon the topographic features and groundwater flow movement. The detailed explanation (along with data and source codes) of the versions can be found in following links:
References:
Oki, T. and Y. C. Sud, 1998: Design of Total Runoff Integrating Pathways (TRIP)-a global river channel network. Earth Interact., 2, doi:10.1175/1087-3562(1998)002<0001:DOTRIP>2.3.CO;2.
Oki, T., T. Nishimura, and P. A. Dirmeyer, 1999: Assessment of annual runoff from land surface models using Total Runoff Integrating Pathways (TRIP). J. Meteorol. Soc. Jpn., 77, 135–255.