Correlation and causation in tree‐ring‐based reconstruction of paleohydrology in cold semiarid regions

Abstract

AbstractThis paper discusses ways in which the tree‐ring‐based reconstruction of paleohydrology can be better understood and better utilized to support water resource management, especially in cold semiarid regions. The relationships between tree growth as represented by tree ring chronologies (TRCs), runoff (Q), precipitation (P), and evapotranspiration (ET) are discussed and analyzed within both statistical and hydrological contexts. Data from the Oldman River Basin (OMRB), Alberta, Canada, are used to demonstrate the relevant issues. Instrumental records of Q and P data were available while actual ET was estimated using a lumped conceptual hydrological model developed in this study. Correlation analysis was conducted to explore the relationships between TRCs and each of Q, P, and ET over the entire historical record (globally) as well as locally in time within the wet and dry subperiods. Global and local correlation strengths and linear relationships appear to be substantially different. This outcome particularly affects tree‐ring‐based inferences about the hydrology of wet and dry episodes when reconstructions are made using regression models. Important findings include (i) reconstruction of paleo‐runoff may not be as credible as paleo‐precipitation and paleo‐evapotranspiration; (ii) a moving average window of P and ET larger than 1 year might be necessary for reconstruction of these variables; and (iii) the long‐term mean of reconstructed P, Q, and ET leads us to conclude that there is uncertainty about the past climate. Finally, we suggest using the topographic index to prejudge side suitability for dendrohydrological analysis.