Unimpaired runoff is important for legal and scientific reasons. Since human development continues to alter watersheds, unimparied runoff provide fixed frames of references for flow rates. The reason unimpaired runoff is important is because long-term hydrologic records are often used to develop relationships between precipitation, runoff, and water supply. By removing changes in the timing between precipitation and runoff due to human influences, the long-term relationships will be more useful.
Calculating unimparied runoff is also extremely important in identifying long-term climate change impacts. By subtracting the known human influences on a long-term hydrologic record, the records may still show signs of a long-term change. These long-term signals are sometimes described as long-term climate change. It is still possible that the long-term climate signal is caused by larger scale antropogenic sources.
The following is a list of some examples of use of unimpaired runoff calculations: