Comparative Hydrology Across Physiographic and Climatic Diversity

A search for simple patterns and predictability

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The bulk of catchment science literature consist of ‘unique’ case studies describing the complex interaction of soils, water, vegetation, topography and geology at individual sites. Yet, the uniqueness of individual sites makes it difficult to transfer findings to new locations and facilitate understanding and prediction in other catchments. In this thesis we use a comparative approach by searching for general behaviour among several hundred catchments located across the contiguous United States to develop transferable theories and facilitate understanding and prediction at other sites. The thesis consist of an introduction to elucidate the use of the comparative approach. Subsequently we present three chapters that use this comparative approach to test multiple hypotheses. (I) We search for appropriate model structures to facilitate improved precipitation-streamflow simulations at the catchment scale. Results indicate that several catchment properties can support the choice for appropriate model structures but choices are associated with large uncertainty. (II) We develop an analytical framework to organise the seasonal partitioning of water for a wide range of settings and show how this framework can facilitate in synthesising understanding of catchment functioning for a wide range of time-scales. (III) We expose how snowfall influences the partitioning of water at the annual time-scale. Results indicate that the projected precipitation shift from snowfall to rain, due to global rising temperatures, may significantly decrease the annual streamflow of catchments that currently receive a large fraction of their precipitation as snowfall. Finally, we conclude that although findings of the individual chapters are valuable, physical understanding is lacking. Additionally there is no common framework to organise the findings within the context of other studies. Both aspects hamper practical and scientific progress to effectively handle many water-related challenges.