Spatial cross‐correlation patterns of European low, mean and high flows

Kerstin Stahl,Lukas Gudmundsson,Lena M. Tallaksen

doi:10.1002/hyp.7807

Abstract

AbstractLow and high flows are associated with different hydrological processes. High flows correspond to the direct response of catchments to water input, whereas low flows occur in pronged dry periods and are governed by depleting storages. Therefore, the inter‐annual dynamics of high and low flows are often considered to be independent. To shed light on this assumption, we analysed a pan‐European dataset of 615 streamflow records, summarized as time series of annual streamflow percentiles (5th, 10th, …, 95th). The analysis was based on comparing the spatial cross‐correlation patterns derived from the different percentile series. Their interrelation was visualized by projecting them into a low‐dimensional space. We found that large parts of the cross‐correlations of the percentile series can be summarized by one dominating component. This component represents geographical continuous regions in Europe of correlated streamflow. Departures from this mean pattern occurred for low and high flows and were characterized by the corresponding spatial correlation functions. Generally, spatial correlations appear to be stronger for high flows than for mean flows, particularly for short distances (<400 km). Low flows, on the other hand, have the lowest spatial correlations for short distances. For longer distances (>800 km), this pattern reverses and the spatial correlation of low flows become largest. This discrepancy between low and high flows suggests that hydrological systems are more homogeneously linked to climatic fluctuations under wet conditions. Under dry conditions, local catchment properties appear to play a larger role in translating climatic fluctuations into hydrological response. Copyright © 2010 John Wiley & Sons, Ltd.

Highlights

Terrestrial water stores and fluxes are key variables controlling many aspects of ecosystem- and climate dynamics
This study investigates the low-frequency components of observed monthly river flow from a large number of small catchments in Europe
The fraction of low-frequency variance of runoff, increases under drier and warmer conditions where catchments respond less directly to precipitation input

Summary

Introduction

Terrestrial water stores and fluxes are key variables controlling many aspects of ecosystem- and climate dynamics. On large (e.g. ecosystem and landscape) scales, these small scale principles are often not sufficient to explain the full range of natural variability. The reasons for this are manifold and rooted in the complexity of environmental systems. Raich and Potter , 1995; Clark et al, 2001] The rationale underlying this is based on the fact that many small scale processes are controlled by the availability of water, energy or nutrients. Other interesting aspects are nutrient and carbon cycling, which largely depend on average water availability [e.g. Davidson et al, 2000; Reichstein et al, 2003; Lohse et al, 2009; Ju et al, 2010]. Theoretical [e.g. Porporato et al, 2004] and experimental [e.g. Knapp et al, 2002; Miller et al, 2005; Knorr and Blodau, 2009] investigations have shown that changes in the dynamical properties of terrestrial water availability may lead to large changes in carbon and nutrient dynamics

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