Since these calculations involve many assumptions, they tend to be more accurate for either smaller watersheds or when expressed as longer period averages.
Since human development continues to alter watersheds, unimpaired runoff provides fixed frames of references for flow rates.
By removing changes in the timing between precipitation and runoff due to human influences, the long-term relationships will be more useful.
Calculating unimpaired runoff is also extremely important in identifying long-term climate change impacts.
Unimpaired runoff calculations are used extensively in western United States states such as California for water resources management applications, particularly in the calculation of water year classifications and river indexes.