To what extent do landscape structure and climate control watershed hydrologic response?

The hydrology of any landscape is closely coupled with other landscape features such as topographic structure, vegetation, climate, geology, etc. An understanding of these relationships will provide answers to crutial hydrologic questions such as, "how fast does water move through a given system", "how important is evapotranspiration", and "what is the function of streams in a natural setting". Quantitatively, this information will help us to develop low-dimensional and falsifiable hydrologic models and more reliably predict the response of ungauged basins. These models are crucial to the development and testing of a unifying similarity theory of watershed hydrology based on dimensionless indices that capture both the internal structure of landscapes (geomorphology, pedology and vegetation patterns) and prevailing climate characteristics.

The innovation of the proposed research lies in the fact that we will (i) apply a bottom-up as well as a top-down dimensional analysis to observations from a large number of watersheds in various climate regions in the US, and (ii) regionalize these similarity measures in an uncertainty framework to derive constraints on hydrologic behavior in ungauged basins. This unifying similarity theory of watershed hydrology will enhance our fundamental understanding of landscape functioning in the hydrological cycle and will promote the development of techniques that permit an integrated analysis of water (and eventually solute) budgets at the watershed scale, as well as of the effects of ecosystem disturbance and land use change on these budgets.

Advancement our understanding of watershed-scale hydrologic response (e.g. stream flow characteristics) is made possible by focusing on the geomorphologic and ecologic controls on hydrological processes of landscapes in different climate settings.

1. When and how does landscape structure control the hydrologic response?
2. What are appropriately lumped state variables that can reproduce hydrologic signatures?
3. Which watershed similarity measures correlate with hydrologic response?
4. How can we regionalize these similarity indices in an uncertainty framework to establish constraints on watershed behavior?
5. How reliable are ensemble hydrologic model predictions, constrained by these similarity indices, and applied to ungauged basins?

Construct a novel similarity theory of watershed hydrology and an associated suite of models (of varying complexity) that will provide new insights into the hydrologic driving mechanisms at a wide range of space and time scales. This understanding will be based on both process understanding (bottom-up approach) and empirical evidence (top-down approach). It will help to:

1. explain observed patterns of hydrological behavior over multiple space-time scales in terms of the underlying climate, soil, vegetation, and topography controls;
2. achieve a new approach to watershed classification based on similarity measures derived from dimensional analysis; and
3. constrain ensemble model predictions at ungauged locations through the regionalization of similarity measures.