Slowflow Signatures of Sustainable Water Resources

Land transformation changes the sustainability of water resources by (a) altering the vegetation, impervious landcover, and drainage of the land surface hydrology system; (b) increasing withdrawals from surface and groundwater systems to support human water use; and (c) re-engineering the water budget through water and wastewater infrastructure that conveys interbasin water transfers and modifies both recharge and subsurface drainage. Slowflow derived from observed streamflow integrates watershed-scale hydrologic forcings and cumulative landscape changes. Multiple slowflow indices derived from USGS streamflow records are used to frame an endpoint mixing model of dominant hydrologic processes and human hydrologic alteration. Multimetric slowflow fingerprints can support more refined process-based inferences, distinguishing, e.g., changes in hydrologic response - (runoff and recharge) from changes in hydraulic response (effective aquifer drainage) in regional streamflow analysis. Examples drawn from USGS streamflow records along the urban-rural landuse gradient in the watersheds of the Baltimore Ecosystem Study (an NSF Urban Long Term Ecological Research site in the Baltimore Metropolitan area) and piedmont Hydroclimatic Data Network (HCDN) basins in the Chesapeake Bay watershed, are used to illustrate multimetric fingerprinting of slowflow response. Within the inherent limits of equifinality in observed streamflow response, multimetric slowflow analysis can refine the signature and attribution of hydroclimatic variability and human hydrologic alteration inferred from regional streamflow information.