An investigation into the Flow Duration Curve in eastern United States : environmental controls and prediction at ungauged basins

The Flow Duration Curve (FDC) is a probabilistic flow representation relevant to streamflow investigation and physical understanding given its use in wide range of hydrological and ecological applications. A regional study that investigates FDCs and their prediction at ungauged catchments is important to develop causal models and provide insights to solve issues of water resources planning and management of aquatic ecosystems and habitats. Hydrological modelling and model parametrization in gauged and ungauged catchments are fundamental steps preceding the regional investigation of flow response using FDC. By means of Sacramento rainfall-runoff model (SAC-SMA), in 73 catchments from the eastern United States, I investigated the effect of SAC-SMA a priori parameters in the constrained calibration of the model. This analysis revealed and discussed limitations of a priori parameters that are intensively used to facilitate model calibration and make predictions at ungauged basins (PUB). The PUB using parameter transfer within homogeneous regions of similar climate and flow characteristics outweighed in performance the a priori parameters. The FDC was advantageous in revealing the effect of lack of efficiency and bias. A parameter regionalization approach is more efficient for PUB than a priori parameters. The ultimate limitations of the within-region parameter transfer are recognized and discussed. The interaction between climate and landscape properties was central to develop the physical understanding of the FDC. The high precipitation variability does not necessarily lead to FDC of a steep slope. Characteristics of the catchment— equivalent to a precipitation filter— interplayed with the precipitation and affected FDC shapes. The analysis highlighted the role of soil infiltration rates in specific conditions of soil moisture storage capacity and predominant runoff generation mechanism. The study revealed that processes underlying FDC and the FDC shapes are by far more complex than being characterized in the wider literature using characteristics of landscape or climate. In conditions of humid climate and perennial flow, a meta-analysis utilizing a process-based investigation showed that mean monthly runoff FDC —readily available at ungauged catchments—predicts only FDC middle third (exceedance probabilities between 33% and 66%). The method is constrained by the value of flow variability (slope of the FDC).Forestry, Faculty ofGraduat