A nonparametric approach for paleohydrologic reconstruction of annual streamflow ensembles

Abstract

[1] As multicentury records of natural hydrologic variability, tree ring reconstructions of streamflow have proven valuable in water resources planning and management. All previous reconstructions have used parametric methods, most often regression, to develop a model relating a set of tree ring data to a target hydrology. In this paper, we present the first development and application of a K nearest neighbor (KNN) nonparametric method to reconstruct naturalized annual streamflow ensembles from tree ring chronology data in the Upper Colorado River Basin region. The method is developed using tree ring chronologies from the period 1400-2005 and naturalized streamflow from the period 1906-2005 at the important Lees Ferry, Arizona, gauge on the Colorado River to develop annual streamflow ensembles for this gauge for the 1400-1905 period. The proposed KNN algorithm was developed and tested using cross validation for the overlap period, i.e., the contemporary observed period for which both the tree ring and streamflow data are available . The cross-validated streamflow reconstructions for the selected contemporary period compare very well with the observed flows and also with published parametric streamflow reconstructions for this gauge. The proposed nonparametric method provides an ensemble of streamflows for each year in the paleohydrologic reconstruction period and, consequently, a more realistic asymmetric confidence interval than one obtained through most parametric approaches. Also, the K nearest neighbors are obtained only from the tree ring chronology data, and thus, the method can be used to reconstruct structured and even nonnumerical data for use in water resources modeling.

Predicting regime shifts in flow of the Colorado River

“…A set of nine paleohydrologic reconstructions of annual streamflows (starting in 1400) for the Lees Ferry gauge was developed by Gangopadhyay et al [2009] (Figure 2). The methodology for developing the reconstructions is based on the K nearest neighbor (KNN) nonparametric method [ Gangopadhyay et al , 2009].…”

“…A set of nine paleohydrologic reconstructions of annual streamflows (starting in 1400) for the Lees Ferry gauge was developed by Gangopadhyay et al [2009] (Figure 2). The methodology for developing the reconstructions is based on the K nearest neighbor (KNN) nonparametric method [ Gangopadhyay et al , 2009]. The method used tree ring chronologies from the period 1400–2005 in the UCRB region and naturalized streamflow for the period 1906–2005 at the Lees Ferry, Arizona gauge on the Colorado River to develop annual streamflow ensembles for this gauge for the 1400–2005 period.…”

“…Paleohydrologic reconstructions provide robust information regarding the hydrologic state of basins – dry or wet, particularly in the southwestern United States. Gangopadhyay et al [2009] analyzed seven paleohydrologic reconstructions for the UCRB (at Lees Ferry, AZ) and found that, although the reconstructed streamflow magnitudes differ among the reconstructions, all seven reconstructions were synchronous in their determination of the dry and wet spell lengths [see Gangopadhyay et al , 2009, Figure 4]. In this paper, we analyze wet and dry spell statistics from a set of paleohydrologic reconstructions [ Gangopadhyay et al , 2009].…”

A Tree-Ring-Based Reconstruction of Delaware River Basin Streamflow Using Hierarchical Bayesian Regression

“…In this paper we consider only the continuous common record and do not consider expectation-maximization (EM) or related algorithms (Dempster et al 1977;Schneider 2001) for gap filling. A successful model also needs to preserve the correlation of streamflow across sites to properly constrain stochastic simulations of multireservoir operation (Gangopadhyay et al 2009).…”

The role of palaeoecological records in assessing ecosystem services

“…A good example of this approach can be found in a project that determined long-term variability in the flow of the Upper Colorado River (Gangopadhyay et al, 2009). In this study, the authors compared the instrumental record of past river flows available from the Lees Ferry Gauge data (spanning the interval 1906e2005) with tree-ring widths spanning the same interval of time from a number of living trees within the catchment.…”