Scaling and Regionalization of Flow Duration Curve Across the Contiguous United States
The ﬂow duration curve (FDC) is a signature catchment characteristic that depicts graphically the relationship between the exceedance probability of streamﬂow and its magnitude. This curve is relatively easy to create and interpret, and is used widely for hydrologic analysis, water quality management, and the design of hydroelectric power plants (among others). In a recent paper, Vrugt and Sadegh  proposed the van Genuchten model as parametric expression for the FDC. This model and other soil water retention functions were tested by Sadegh et al.  and found to closely describe the FDCs of the MOPEX data set. In this thesis, we apply the similar media concept of Miller and Miller  to surface hydrology and analyze the spatial variability of the FDC in the contiguous US. The scaling method is used to coalesce the FDCs of the MOPEX data set into a "mean" reference curve for the contiguous US using single scaling factors for the FDC of the watersheds. Results demonstrate that the scaling factors exhibit a strong geographical trend with spatial patterns similar to those observed in US precipitation maps. Regionalization of the scaling factors is particularly successful for the peak ﬂows of the FDC. Cokriging with environmental covariates such as the annual rainfall amount of each watershed improves further the prediction of the FDC for ungauged basins.