Articles | Volume 13, issue 12
Research article
18 Dec 2017
Research article |  | 18 Dec 2017

Hydroclimate variability in Scandinavia over the last millennium – insights from a climate model–proxy data comparison

Kristina Seftigen, Hugues Goosse, Francois Klein, and Deliang Chen

Abstract. The integration of climate proxy information with general circulation model (GCM) results offers considerable potential for deriving greater understanding of the mechanisms underlying climate variability, as well as unique opportunities for out-of-sample evaluations of model performance. In this study, we combine insights from a new tree-ring hydroclimate reconstruction from Scandinavia with projections from a suite of forced transient simulations of the last millennium and historical intervals from the CMIP5 and PMIP3 archives. Model simulations and proxy reconstruction data are found to broadly agree on the modes of atmospheric variability that produce droughts–pluvials in the region. Despite these dynamical similarities, large differences between simulated and reconstructed hydroclimate time series remain. We find that the GCM-simulated multi-decadal and/or longer hydroclimate variability is systematically smaller than the proxy-based estimates, whereas the dominance of GCM-simulated high-frequency components of variability is not reflected in the proxy record. Furthermore, the paleoclimate evidence indicates in-phase coherencies between regional hydroclimate and temperature on decadal timescales, i.e., sustained wet periods have often been concurrent with warm periods and vice versa. The CMIP5–PMIP3 archive suggests, however, out-of-phase coherencies between the two variables in the last millennium. The lack of adequate understanding of mechanisms linking temperature and moisture supply on longer timescales has serious implications for attribution and prediction of regional hydroclimate changes. Our findings stress the need for further paleoclimate data–model intercomparison efforts to expand our understanding of the dynamics of hydroclimate variability and change, to enhance our ability to evaluate climate models, and to provide a more comprehensive view of future drought and pluvial risks.

Short summary
Comparisons of proxy data to GCM-simulated hydroclimate are still limited and inter-model variability remains poorly characterized. In this study, we bring together tree-ring paleoclimate evidence and CMIP5–PMIP3 model simulations of the last millennium hydroclimate variability across Scandinavia. We explore the consistency between the datasets and the role of external forcing versus internal variability in driving the hydroclimate changes regionally.