Abstract

This article presents a new approach to quantifying pluriannual hydrological memory, using exclusively streamflow and climate data. The rainfall--runoff relationship is analyzed through the concept of elasticity, focusing on the relation between the annual anomalies of runoff yield and humidity index. We identify Catchment Forgetting Curves (CFC) to quantify pluriannual catchment memory, considering not only the current year's humidity anomaly but also the anomalies of the preceding years. CFCs are parameterized using a Gamma distribution. The variability of CFCs is investigated on a set of 158 Swedish and 527 French catchments. As expected, French catchments overlying powerful aquifers exhibit a long memory. In Sweden, the expected effect of the lakes is less clear. Overall, aridity appears to be one of the main drivers of catchment memory in both countries. Our work underlines the need to account for catchment memory in order to produce meaningful and geographically coherent elasticity indices.

Highlights

  • 1.1 Catchment memoryA catchment receives precipitation from the atmosphere, a water amount that is either stored in soils, biota, snow/glaciers, lakes/wetlands, and aquifers, or returned to the atmosphere, exported by the river, or exported to regional aquifers

  • The rainfall–runoff relationship is analyzed through the concept of elasticity, focusing on the relation between the annual anomalies of runoff yield and humidity index

  • 4 Conclusions 4.1 Synthesis In this article, we proposed a new approach to quantifying catchment pluriannual memory, requiring only the knowledge of annual discharge data and climatic inputs

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Summary

Introduction

1.1 Catchment memoryA catchment receives precipitation from the atmosphere, a water amount that is either stored in soils, biota, snow/glaciers, lakes/wetlands, and aquifers, or returned to the atmosphere (evaporated), exported by the river (as streamflow), or exported to regional aquifers (as intercatchment groundwater flow). The relative distribution between these fluxes depends on the 15 physical characteristics of the catchment, and on the recent climatic sequence: The response of a catchment to incoming precipitation depends largely on its wetness (i.e., on the more or less saturated state of soils and wetlands within the catchment). The objective of this paper is to characterize catchment memory, in order to understand the time during which the past 20 climatic sequence will affect catchment response. We wish here to follow the experimental psychologist Ebbinghaus (1885) in proposing forgetting curves, which will describe the decline of memory in time.

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