hydrologic regions The smaller units, with fixed boundaries, into which large tracts of country are divided for the purpose of collecting hydrologic data. The establishment of hydrologic regions allows data to be collected on the same basis from year to year and so facilitates historical analysis. Wellidentified regions have a common climate and geologic and topographical structure, so that the hydrologic cycle operates fairly uniformly within each region.

hydrologic region One of the smaller units, with fixed boundaries, into which large tracts of country, sharing a common climate and geologic and topographical structure, are divided for the purpose of collecting hydrologic data on the same basis from year to year, thus facilitating historical analysis.