Using celerity to measure hydrological processes

The last major advance in catchment hydrology was the discovery that while headwaters respond promptly to changes in water input, much of the resulting river flow is months or years old. The classical way of testing catchment models is to use measurements that reflect celerities—the measure of how fast the storage of water responds to a perturbation—of the response to an input event such as changes in rain or snowfall. However, McDonnell and Beven point out that testing catchment models against both celerity and tracer velocity—the measure of how fast the water particles are moving—can help improve model realism and reduce uncertainties and errors.