Direct Versus Indirect Tree Ring Reconstruction of Annual Discharge of Chemora River, Algeria

David Meko,Said Slimani,Ramzi Touchan,Dalila Kherchouche

doi:10.3390/f11090986

David Meko, Said Slimani + Show 2 more

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https://doi.org/10.3390/f11090986

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Abstract

Annual river discharge is a critical variable for water resources planning and management. Tree rings are widely used to reconstruct annual discharge, but errors can be large when tree growth fails to respond commensurately to hydrologically important seasonal components of climate. This paper contrasts direct and indirect reconstruction as statistical approaches to discharge reconstruction for the Chemora River, in semi-arid northeastern Algeria, and explores indirect reconstruction as a diagnostic tool in reconstruction error analysis. We define direct reconstruction as predictions from regression of annual discharge on tree ring data, and indirect reconstruction as predictions from a four-stage process: (1) regression of precipitation on tree rings, (2) application of the regression model to get reconstructed precipitation for grid cells over the basin, (3) routing of reconstructed precipitation through a climatological water balance (WB) model, and (4) summing model runoff over cells to get the reconstructed discharge at a gage location. For comparative purposes, the potential predictors in both modeling approaches are the same principal components of tree ring width chronologies from a network of drought-sensitive sites of Pinus halepensis and Cedrus atlantica in northern Algeria. Results suggest that both modeling approaches can yield statistically significant reconstructions for the Chemora River. Greater accuracy and simplicity of the direct method are countered by conceptual physical advantages of the indirect method. The WB modeling inherent to the indirect method is useful as a diagnostic tool in error analysis of discharge reconstruction, points out the low and declining importance of snowmelt to the river discharge, and gives clues to the cause of severe underestimation of discharge in the outlier high-discharge year 1996. Results show that indirect reconstruction would benefit most in this basin from tree ring resolution of seasonal precipitation.

Highlights

Tree ring reconstructions of river discharge have long been used to place recent and projected hydroclimatic variability in a multi-century context [1,2]
Tree ring reconstructions of river discharge routed through a lake water-balance (WB) model helped corroborate multi-century droughts in the Sierra Nevada of California inferred from radiocarbon-dated stumps exposed in rivers and lakes [3]
We address the strengths and weaknesses of direct versus indirect reconstruction of annual discharge of the Chemora River, northeastern Algeria

Summary

Introduction

Tree ring reconstructions of river discharge have long been used to place recent and projected hydroclimatic variability in a multi-century context [1,2]. The central idea is to statistically reconstruct climatic variables, such as precipitation (P) and temperature (T), that directly impact tree growth, and use the reconstructed variables as inputs to a physically based hydrologic model whose output includes runoff or river discharge [4,5,6,7]. We call such reconstruction of discharge through the intermediary of a hydrologic model “indirect”

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