The Hydromorphology of an Urbanizing Watershed Using Multivariate Elasticity

Abstract:

Hydromorphology concerns the structure and evolution of watershed systems over time (e.g. years, decades, and centuries). We introduce a generalized multivariate approach for exploring hydromorphological problems that involves estimation of the multivariate sensitivity or elasticity of streamflow to changes in climate, water use, and land use. Key advantages of the method presented are that it does not require a model assumption yet provides confidence intervals and hypothesis tests for the resulting elasticities.

A case study highlights the influence of urbanization on the complete range of streamflow and shows that accounting for the simultaneous interactions among land use, climate, and water use is a necessary component for understanding the influence of urbanization on streamflow regimes. All streamflows are influenced to some extent by changes in climate, land use, and water use. However, in the case study the most striking sensitivities to all three factors are associated with low streamflows.

These results imply that future hydromorphological changes in the case study basin will tend to exacerbate average annual streamflows and droughts more than floods. The extremely large positive sensitivity of low flows to changes in land use departs from the conclusions of several previous studies (e.g. Brandes et al. 2005). Investigations of a much broader class of basins are needed to support and generalize this new result of sensitive response of low streamflows. Overall, the study demonstrates that streamflow is sensitive to changes in climate, land use, and water use. All three of these effects must be considered simultaneously to fully understand the hydromorphology of a watershed. It is our hope that future studies will extend this methodology to a much wider and richer cross section of watersheds.