INSTRUMENTING HYDROLOGIC OBSERVATORIES FOR RAINFALL-RUNOFF RESEARCH: A CASE FOR THE TOPDOWN APPROACH

The proposed CUAHSI environmental observatories provide unprecedented opportunities for developing new process insights into the rainfall-runoff process. Because the proposed observatories are at a scale considerably larger than the traditional headwater research catchment, new approaches to gauging will be required. This talk argues that the now-standard bottom-up, reductionist approaches of the past many decades may need to be replaced by topdown approaches to gauging and watershed discretization. The observatories may be a catalyst for changing the way that we gauge and instrument watersheds for rainfall-runoff research: from invasive to non-invasive, from purely physical characterization to isotopic, geochemical and biogeochemical characterization, from physics-based to ecological form and process –based, from point based to pattern based, from single basin studies to inter-comparison and classification of (sub)watersheds, from a linear response focus to defining thresholds, and from measurement acceptance to dealing with measurement uncertainty. The topdown approach is argued to be a way to make watershed instrumentation for rainfall-runoff process research less ad hoc.